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This also involves renaming src/include/utils/hashutils.h, which becomes src/include/common/hashfn.h. Perhaps an argument can be made for keeping the hashutils.h name, but it seemed more consistent to make it match the name of the file, and also more descriptive of what is actually going on here. Patch by me, reviewed by Suraj Kharage and Mark Dilger. Off-list advice on how not to break the Windows build from Davinder Singh and Amit Kapila. Discussion: http://postgr.es/m/CA+TgmoaRiG4TXND8QuM6JXFRkM_1wL2ZNhzaUKsuec9-4yrkgw@mail.gmail.com
521 lines
14 KiB
C
521 lines
14 KiB
C
/* -------------------------------------------------------------------------
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*
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* contrib/sepgsql/uavc.c
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*
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* Implementation of userspace access vector cache; that enables to cache
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* access control decisions recently used, and reduce number of kernel
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* invocations to avoid unnecessary performance hit.
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*
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* Copyright (c) 2011-2020, PostgreSQL Global Development Group
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*
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* -------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "catalog/pg_proc.h"
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#include "commands/seclabel.h"
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#include "common/hashfn.h"
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#include "sepgsql.h"
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#include "storage/ipc.h"
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#include "utils/guc.h"
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#include "utils/memutils.h"
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/*
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* avc_cache
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*
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* It enables to cache access control decision (and behavior on execution of
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* trusted procedure, db_procedure class only) for a particular pair of
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* security labels and object class in userspace.
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*/
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typedef struct
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{
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uint32 hash; /* hash value of this cache entry */
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char *scontext; /* security context of the subject */
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char *tcontext; /* security context of the target */
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uint16 tclass; /* object class of the target */
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uint32 allowed; /* permissions to be allowed */
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uint32 auditallow; /* permissions to be audited on allowed */
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uint32 auditdeny; /* permissions to be audited on denied */
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bool permissive; /* true, if permissive rule */
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bool hot_cache; /* true, if recently referenced */
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bool tcontext_is_valid;
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/* true, if tcontext is valid */
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char *ncontext; /* temporary scontext on execution of trusted
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* procedure, or NULL elsewhere */
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} avc_cache;
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/*
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* Declaration of static variables
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*/
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#define AVC_NUM_SLOTS 512
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#define AVC_NUM_RECLAIM 16
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#define AVC_DEF_THRESHOLD 384
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static MemoryContext avc_mem_cxt;
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static List *avc_slots[AVC_NUM_SLOTS]; /* avc's hash buckets */
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static int avc_num_caches; /* number of caches currently used */
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static int avc_lru_hint; /* index of the buckets to be reclaimed next */
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static int avc_threshold; /* threshold to launch cache-reclaiming */
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static char *avc_unlabeled; /* system 'unlabeled' label */
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/*
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* Hash function
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*/
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static uint32
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sepgsql_avc_hash(const char *scontext, const char *tcontext, uint16 tclass)
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{
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return hash_any((const unsigned char *) scontext, strlen(scontext))
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^ hash_any((const unsigned char *) tcontext, strlen(tcontext))
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^ tclass;
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}
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/*
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* Reset all the avc caches
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*/
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static void
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sepgsql_avc_reset(void)
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{
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MemoryContextReset(avc_mem_cxt);
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memset(avc_slots, 0, sizeof(List *) * AVC_NUM_SLOTS);
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avc_num_caches = 0;
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avc_lru_hint = 0;
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avc_unlabeled = NULL;
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}
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/*
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* Reclaim caches recently unreferenced
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*/
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static void
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sepgsql_avc_reclaim(void)
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{
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ListCell *cell;
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int index;
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while (avc_num_caches >= avc_threshold - AVC_NUM_RECLAIM)
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{
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index = avc_lru_hint;
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foreach(cell, avc_slots[index])
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{
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avc_cache *cache = lfirst(cell);
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if (!cache->hot_cache)
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{
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avc_slots[index]
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= foreach_delete_current(avc_slots[index], cell);
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pfree(cache->scontext);
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pfree(cache->tcontext);
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if (cache->ncontext)
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pfree(cache->ncontext);
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pfree(cache);
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avc_num_caches--;
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}
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else
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{
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cache->hot_cache = false;
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}
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}
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avc_lru_hint = (avc_lru_hint + 1) % AVC_NUM_SLOTS;
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}
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}
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/* -------------------------------------------------------------------------
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*
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* sepgsql_avc_check_valid
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*
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* This function checks whether the cached entries are still valid. If
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* the security policy has been reloaded (or any other events that requires
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* resetting userspace caches has occurred) since the last reference to
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* the access vector cache, we must flush the cache.
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*
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* Access control decisions must be atomic, but multiple system calls may
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* be required to make a decision; thus, when referencing the access vector
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* cache, we must loop until we complete without an intervening cache flush
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* event. In practice, looping even once should be very rare. Callers should
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* do something like this:
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*
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* sepgsql_avc_check_valid();
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* do {
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* :
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* <reference to uavc>
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* :
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* } while (!sepgsql_avc_check_valid())
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*
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* -------------------------------------------------------------------------
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*/
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static bool
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sepgsql_avc_check_valid(void)
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{
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if (selinux_status_updated() > 0)
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{
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sepgsql_avc_reset();
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return false;
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}
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return true;
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}
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/*
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* sepgsql_avc_unlabeled
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*
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* Returns an alternative label to be applied when no label or an invalid
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* label would otherwise be assigned.
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*/
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static char *
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sepgsql_avc_unlabeled(void)
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{
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if (!avc_unlabeled)
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{
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security_context_t unlabeled;
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if (security_get_initial_context_raw("unlabeled", &unlabeled) < 0)
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ereport(ERROR,
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(errcode(ERRCODE_INTERNAL_ERROR),
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errmsg("SELinux: failed to get initial security label: %m")));
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PG_TRY();
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{
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avc_unlabeled = MemoryContextStrdup(avc_mem_cxt, unlabeled);
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}
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PG_FINALLY();
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{
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freecon(unlabeled);
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}
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PG_END_TRY();
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}
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return avc_unlabeled;
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}
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/*
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* sepgsql_avc_compute
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*
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* A fallback path, when cache mishit. It asks SELinux its access control
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* decision for the supplied pair of security context and object class.
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*/
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static avc_cache *
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sepgsql_avc_compute(const char *scontext, const char *tcontext, uint16 tclass)
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{
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char *ucontext = NULL;
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char *ncontext = NULL;
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MemoryContext oldctx;
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avc_cache *cache;
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uint32 hash;
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int index;
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struct av_decision avd;
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hash = sepgsql_avc_hash(scontext, tcontext, tclass);
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index = hash % AVC_NUM_SLOTS;
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/*
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* Validation check of the supplied security context. Because it always
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* invoke system-call, frequent check should be avoided. Unless security
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* policy is reloaded, validation status shall be kept, so we also cache
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* whether the supplied security context was valid, or not.
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*/
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if (security_check_context_raw((security_context_t) tcontext) != 0)
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ucontext = sepgsql_avc_unlabeled();
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/*
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* Ask SELinux its access control decision
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*/
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if (!ucontext)
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sepgsql_compute_avd(scontext, tcontext, tclass, &avd);
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else
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sepgsql_compute_avd(scontext, ucontext, tclass, &avd);
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/*
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* It also caches a security label to be switched when a client labeled as
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* 'scontext' executes a procedure labeled as 'tcontext', not only access
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* control decision on the procedure. The security label to be switched
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* shall be computed uniquely on a pair of 'scontext' and 'tcontext',
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* thus, it is reasonable to cache the new label on avc, and enables to
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* reduce unnecessary system calls. It shall be referenced at
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* sepgsql_needs_fmgr_hook to check whether the supplied function is a
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* trusted procedure, or not.
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*/
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if (tclass == SEPG_CLASS_DB_PROCEDURE)
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{
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if (!ucontext)
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ncontext = sepgsql_compute_create(scontext, tcontext,
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SEPG_CLASS_PROCESS, NULL);
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else
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ncontext = sepgsql_compute_create(scontext, ucontext,
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SEPG_CLASS_PROCESS, NULL);
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if (strcmp(scontext, ncontext) == 0)
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{
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pfree(ncontext);
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ncontext = NULL;
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}
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}
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/*
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* Set up an avc_cache object
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*/
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oldctx = MemoryContextSwitchTo(avc_mem_cxt);
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cache = palloc0(sizeof(avc_cache));
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cache->hash = hash;
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cache->scontext = pstrdup(scontext);
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cache->tcontext = pstrdup(tcontext);
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cache->tclass = tclass;
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cache->allowed = avd.allowed;
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cache->auditallow = avd.auditallow;
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cache->auditdeny = avd.auditdeny;
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cache->hot_cache = true;
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if (avd.flags & SELINUX_AVD_FLAGS_PERMISSIVE)
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cache->permissive = true;
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if (!ucontext)
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cache->tcontext_is_valid = true;
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if (ncontext)
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cache->ncontext = pstrdup(ncontext);
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avc_num_caches++;
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if (avc_num_caches > avc_threshold)
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sepgsql_avc_reclaim();
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avc_slots[index] = lcons(cache, avc_slots[index]);
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MemoryContextSwitchTo(oldctx);
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return cache;
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}
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/*
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* sepgsql_avc_lookup
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*
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* Look up a cache entry that matches the supplied security contexts and
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* object class. If not found, create a new cache entry.
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*/
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static avc_cache *
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sepgsql_avc_lookup(const char *scontext, const char *tcontext, uint16 tclass)
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{
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avc_cache *cache;
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ListCell *cell;
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uint32 hash;
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int index;
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hash = sepgsql_avc_hash(scontext, tcontext, tclass);
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index = hash % AVC_NUM_SLOTS;
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foreach(cell, avc_slots[index])
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{
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cache = lfirst(cell);
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if (cache->hash == hash &&
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cache->tclass == tclass &&
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strcmp(cache->tcontext, tcontext) == 0 &&
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strcmp(cache->scontext, scontext) == 0)
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{
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cache->hot_cache = true;
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return cache;
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}
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}
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/* not found, so insert a new cache */
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return sepgsql_avc_compute(scontext, tcontext, tclass);
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}
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/*
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* sepgsql_avc_check_perms(_label)
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*
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* It returns 'true', if the security policy suggested to allow the required
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* permissions. Otherwise, it returns 'false' or raises an error according
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* to the 'abort_on_violation' argument.
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* The 'tobject' and 'tclass' identify the target object being referenced,
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* and 'required' is a bitmask of permissions (SEPG_*__*) defined for each
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* object classes.
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* The 'audit_name' is the object name (optional). If SEPGSQL_AVC_NOAUDIT
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* was supplied, it means to skip all the audit messages.
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*/
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bool
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sepgsql_avc_check_perms_label(const char *tcontext,
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uint16 tclass, uint32 required,
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const char *audit_name,
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bool abort_on_violation)
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{
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char *scontext = sepgsql_get_client_label();
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avc_cache *cache;
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uint32 denied;
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uint32 audited;
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bool result;
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sepgsql_avc_check_valid();
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do
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{
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result = true;
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/*
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* If the target object is unlabeled, we perform the check using the
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* label supplied by sepgsql_avc_unlabeled().
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*/
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if (tcontext)
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cache = sepgsql_avc_lookup(scontext, tcontext, tclass);
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else
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cache = sepgsql_avc_lookup(scontext,
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sepgsql_avc_unlabeled(), tclass);
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denied = required & ~cache->allowed;
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/*
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* Compute permissions to be audited
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*/
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if (sepgsql_get_debug_audit())
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audited = (denied ? (denied & ~0) : (required & ~0));
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else
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audited = denied ? (denied & cache->auditdeny)
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: (required & cache->auditallow);
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if (denied)
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{
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/*
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* In permissive mode or permissive domain, violated permissions
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* shall be audited to the log files at once, and then implicitly
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* allowed to avoid a flood of access denied logs, because the
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* purpose of permissive mode/domain is to collect a violation log
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* that will make it possible to fix up the security policy.
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*/
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if (!sepgsql_getenforce() || cache->permissive)
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cache->allowed |= required;
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else
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result = false;
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}
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} while (!sepgsql_avc_check_valid());
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/*
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* In the case when we have something auditable actions here,
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* sepgsql_audit_log shall be called with text representation of security
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* labels for both of subject and object. It records this access
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* violation, so DBA will be able to find out unexpected security problems
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* later.
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*/
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if (audited != 0 &&
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audit_name != SEPGSQL_AVC_NOAUDIT &&
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sepgsql_get_mode() != SEPGSQL_MODE_INTERNAL)
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{
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sepgsql_audit_log(denied != 0,
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cache->scontext,
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cache->tcontext_is_valid ?
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cache->tcontext : sepgsql_avc_unlabeled(),
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cache->tclass,
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audited,
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audit_name);
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}
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if (abort_on_violation && !result)
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ereport(ERROR,
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(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
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errmsg("SELinux: security policy violation")));
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return result;
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}
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bool
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sepgsql_avc_check_perms(const ObjectAddress *tobject,
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uint16 tclass, uint32 required,
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const char *audit_name,
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bool abort_on_violation)
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{
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char *tcontext = GetSecurityLabel(tobject, SEPGSQL_LABEL_TAG);
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bool rc;
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rc = sepgsql_avc_check_perms_label(tcontext,
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tclass, required,
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audit_name, abort_on_violation);
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if (tcontext)
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pfree(tcontext);
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return rc;
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}
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/*
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* sepgsql_avc_trusted_proc
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*
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* If the supplied function OID is configured as a trusted procedure, this
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* function will return a security label to be used during the execution of
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* that function. Otherwise, it returns NULL.
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*/
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char *
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sepgsql_avc_trusted_proc(Oid functionId)
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{
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char *scontext = sepgsql_get_client_label();
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char *tcontext;
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ObjectAddress tobject;
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avc_cache *cache;
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tobject.classId = ProcedureRelationId;
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tobject.objectId = functionId;
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tobject.objectSubId = 0;
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tcontext = GetSecurityLabel(&tobject, SEPGSQL_LABEL_TAG);
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sepgsql_avc_check_valid();
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do
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{
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if (tcontext)
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cache = sepgsql_avc_lookup(scontext, tcontext,
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SEPG_CLASS_DB_PROCEDURE);
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else
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cache = sepgsql_avc_lookup(scontext, sepgsql_avc_unlabeled(),
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SEPG_CLASS_DB_PROCEDURE);
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} while (!sepgsql_avc_check_valid());
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return cache->ncontext;
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}
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/*
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* sepgsql_avc_exit
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*
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* Clean up userspace AVC on process exit.
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*/
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static void
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sepgsql_avc_exit(int code, Datum arg)
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{
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selinux_status_close();
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}
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/*
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* sepgsql_avc_init
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*
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* Initialize the userspace AVC. This should be called from _PG_init.
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*/
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void
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sepgsql_avc_init(void)
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{
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int rc;
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/*
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* All the avc stuff shall be allocated in avc_mem_cxt
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*/
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avc_mem_cxt = AllocSetContextCreate(TopMemoryContext,
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"userspace access vector cache",
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ALLOCSET_DEFAULT_SIZES);
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memset(avc_slots, 0, sizeof(avc_slots));
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avc_num_caches = 0;
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avc_lru_hint = 0;
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avc_threshold = AVC_DEF_THRESHOLD;
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/*
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* SELinux allows to mmap(2) its kernel status page in read-only mode to
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* inform userspace applications its status updating (such as policy
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* reloading) without system-call invocations. This feature is only
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* supported in Linux-2.6.38 or later, however, libselinux provides a
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* fallback mode to know its status using netlink sockets.
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*/
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rc = selinux_status_open(1);
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if (rc < 0)
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ereport(ERROR,
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(errcode(ERRCODE_INTERNAL_ERROR),
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errmsg("SELinux: could not open selinux status : %m")));
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else if (rc > 0)
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ereport(LOG,
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(errmsg("SELinux: kernel status page uses fallback mode")));
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/* Arrange to close selinux status page on process exit. */
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on_proc_exit(sepgsql_avc_exit, 0);
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}
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