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Refactor permissions checks for large objects. 

Up to now, ACL checks for large objects happened at the level of
the SQL-callable functions, which led to CVE-2017-7548 because of a
missing check.  Push them down to be enforced in inv_api.c as much
as possible, in hopes of preventing future bugs.  This does have the
effect of moving read and write permission errors to happen at lo_open
time not loread or lowrite time, but that seems acceptable.

Michael Paquier and Tom Lane

Discussion: https://postgr.es/m/CAB7nPqRHmNOYbETnc_2EjsuzSM00Z+BWKv9sy6tnvSd5gWT_JA@mail.gmail.com
This commit is contained in:
Tom Lane 2017-11-09 12:56:07 -05:00
parent 5ecc0d738e
commit ae20b23a9e
6 changed files with 118 additions and 112 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/backend/catalog/objectaddress.c
View File

@ -69,13 +69,13 @@
#include "commands/trigger.h"
#include "foreign/foreign.h"
#include "funcapi.h"
#include "libpq/be-fsstubs.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "parser/parse_func.h"
#include "parser/parse_oper.h"
#include "parser/parse_type.h"
#include "rewrite/rewriteSupport.h"
#include "storage/large_object.h"
#include "storage/lmgr.h"
#include "storage/sinval.h"
#include "utils/builtins.h"

88
src/backend/libpq/be-fsstubs.c
View File

@ -51,11 +51,6 @@
#include "utils/builtins.h"
#include "utils/memutils.h"
/*
* compatibility flag for permission checks
*/
bool lo_compat_privileges;
/* define this to enable debug logging */
/* #define FSDB 1 */
/* chunk size for lo_import/lo_export transfers */
@ -108,14 +103,6 @@ be_lo_open(PG_FUNCTION_ARGS)
lobjDesc = inv_open(lobjId, mode, fscxt);
if (lobjDesc == NULL)
{ /* lookup failed */
#if FSDB
elog(DEBUG4, "could not open large object %u", lobjId);
#endif
PG_RETURN_INT32(-1);
}
fd = newLOfd(lobjDesc);
PG_RETURN_INT32(fd);
@ -163,22 +150,16 @@ lo_read(int fd, char *buf, int len)
errmsg("invalid large-object descriptor: %d", fd)));
lobj = cookies[fd];
/* We don't bother to check IFS_RDLOCK, since it's always set */
/* Permission checks --- first time through only */
if ((lobj->flags & IFS_RD_PERM_OK) == 0)
{
if (!lo_compat_privileges &&
pg_largeobject_aclcheck_snapshot(lobj->id,
GetUserId(),
ACL_SELECT,
lobj->snapshot) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
lobj->id)));
lobj->flags |= IFS_RD_PERM_OK;
}
/*
* Check state. inv_read() would throw an error anyway, but we want the
* error to be about the FD's state not the underlying privilege; it might
* be that the privilege exists but user forgot to ask for read mode.
*/
if ((lobj->flags & IFS_RDLOCK) == 0)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("large object descriptor %d was not opened for reading",
fd)));
status = inv_read(lobj, buf, len);
@ -197,27 +178,13 @@ lo_write(int fd, const char *buf, int len)
errmsg("invalid large-object descriptor: %d", fd)));
lobj = cookies[fd];
/* see comment in lo_read() */
if ((lobj->flags & IFS_WRLOCK) == 0)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("large object descriptor %d was not opened for writing",
fd)));
/* Permission checks --- first time through only */
if ((lobj->flags & IFS_WR_PERM_OK) == 0)
{
if (!lo_compat_privileges &&
pg_largeobject_aclcheck_snapshot(lobj->id,
GetUserId(),
ACL_UPDATE,
lobj->snapshot) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
lobj->id)));
lobj->flags |= IFS_WR_PERM_OK;
}
status = inv_write(lobj, buf, len);
return status;
@ -342,7 +309,11 @@ be_lo_unlink(PG_FUNCTION_ARGS)
{
Oid lobjId = PG_GETARG_OID(0);
/* Must be owner of the largeobject */
/*
* Must be owner of the large object. It would be cleaner to check this
* in inv_drop(), but we want to throw the error before not after closing
* relevant FDs.
*/
if (!lo_compat_privileges &&
!pg_largeobject_ownercheck(lobjId, GetUserId()))
ereport(ERROR,
@ -574,27 +545,13 @@ lo_truncate_internal(int32 fd, int64 len)
errmsg("invalid large-object descriptor: %d", fd)));
lobj = cookies[fd];
/* see comment in lo_read() */
if ((lobj->flags & IFS_WRLOCK) == 0)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("large object descriptor %d was not opened for writing",
fd)));
/* Permission checks --- first time through only */
if ((lobj->flags & IFS_WR_PERM_OK) == 0)
{
if (!lo_compat_privileges &&
pg_largeobject_aclcheck_snapshot(lobj->id,
GetUserId(),
ACL_UPDATE,
lobj->snapshot) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
lobj->id)));
lobj->flags |= IFS_WR_PERM_OK;
}
inv_truncate(lobj, len);
}
@ -770,17 +727,6 @@ lo_get_fragment_internal(Oid loOid, int64 offset, int32 nbytes)
loDesc = inv_open(loOid, INV_READ, fscxt);
/* Permission check */
if (!lo_compat_privileges &&
pg_largeobject_aclcheck_snapshot(loDesc->id,
GetUserId(),
ACL_SELECT,
loDesc->snapshot) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
loDesc->id)));
/*
* Compute number of bytes we'll actually read, accommodating nbytes == -1
* and reads beyond the end of the LO.

110
src/backend/storage/large_object/inv_api.c
View File

@ -51,6 +51,11 @@
#include "utils/tqual.h"
/*
* GUC: backwards-compatibility flag to suppress LO permission checks
*/
bool lo_compat_privileges;
/*
* All accesses to pg_largeobject and its index make use of a single Relation
* reference, so that we only need to open pg_relation once per transaction.
@ -250,47 +255,79 @@ inv_open(Oid lobjId, int flags, MemoryContext mcxt)
Snapshot snapshot = NULL;
int descflags = 0;
/*
* Historically, no difference is made between (INV_WRITE) and (INV_WRITE
* | INV_READ), the caller being allowed to read the large object
* descriptor in either case.
*/
if (flags & INV_WRITE)
{
snapshot = NULL; /* instantaneous MVCC snapshot */
descflags = IFS_WRLOCK | IFS_RDLOCK;
}
else if (flags & INV_READ)
{
snapshot = GetActiveSnapshot();
descflags = IFS_RDLOCK;
}
else
descflags |= IFS_WRLOCK | IFS_RDLOCK;
if (flags & INV_READ)
descflags |= IFS_RDLOCK;
if (descflags == 0)
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid flags for opening a large object: %d",
flags)));
/* Get snapshot. If write is requested, use an instantaneous snapshot. */
if (descflags & IFS_WRLOCK)
snapshot = NULL;
else
snapshot = GetActiveSnapshot();
/* Can't use LargeObjectExists here because we need to specify snapshot */
if (!myLargeObjectExists(lobjId, snapshot))
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_OBJECT),
errmsg("large object %u does not exist", lobjId)));
/*
* We must register the snapshot in TopTransaction's resowner, because it
* must stay alive until the LO is closed rather than until the current
* portal shuts down. Do this after checking that the LO exists, to avoid
* leaking the snapshot if an error is thrown.
*/
if (snapshot)
snapshot = RegisterSnapshotOnOwner(snapshot,
TopTransactionResourceOwner);
/* Apply permission checks, again specifying snapshot */
if ((descflags & IFS_RDLOCK) != 0)
{
if (!lo_compat_privileges &&
pg_largeobject_aclcheck_snapshot(lobjId,
GetUserId(),
ACL_SELECT,
snapshot) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
lobjId)));
}
if ((descflags & IFS_WRLOCK) != 0)
{
if (!lo_compat_privileges &&
pg_largeobject_aclcheck_snapshot(lobjId,
GetUserId(),
ACL_UPDATE,
snapshot) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
lobjId)));
}
/* All set, create a descriptor */
/* OK to create a descriptor */
retval = (LargeObjectDesc *) MemoryContextAlloc(mcxt,
sizeof(LargeObjectDesc));
retval->id = lobjId;
retval->subid = GetCurrentSubTransactionId();
retval->offset = 0;
retval->snapshot = snapshot;
retval->flags = descflags;
/*
* We must register the snapshot in TopTransaction's resowner, because it
* must stay alive until the LO is closed rather than until the current
* portal shuts down. Do this last to avoid uselessly leaking the
* snapshot if an error is thrown above.
*/
if (snapshot)
snapshot = RegisterSnapshotOnOwner(snapshot,
TopTransactionResourceOwner);
retval->snapshot = snapshot;
return retval;
}
@ -312,7 +349,7 @@ inv_close(LargeObjectDesc *obj_desc)
/*
* Destroys an existing large object (not to be confused with a descriptor!)
*
* returns -1 if failed
* Note we expect caller to have done any required permissions check.
*/
int
inv_drop(Oid lobjId)
@ -333,6 +370,7 @@ inv_drop(Oid lobjId)
*/
CommandCounterIncrement();
/* For historical reasons, we always return 1 on success. */
return 1;
}
@ -397,6 +435,11 @@ inv_seek(LargeObjectDesc *obj_desc, int64 offset, int whence)
Assert(PointerIsValid(obj_desc));
/*
* We allow seek/tell if you have either read or write permission, so no
* need for a permission check here.
*/
/*
* Note: overflow in the additions is possible, but since we will reject
* negative results, we don't need any extra test for that.
@ -439,6 +482,11 @@ inv_tell(LargeObjectDesc *obj_desc)
{
Assert(PointerIsValid(obj_desc));
/*
* We allow seek/tell if you have either read or write permission, so no
* need for a permission check here.
*/
return obj_desc->offset;
}
@ -458,6 +506,12 @@ inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes)
Assert(PointerIsValid(obj_desc));
Assert(buf != NULL);
if ((obj_desc->flags & IFS_RDLOCK) == 0)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
obj_desc->id)));
if (nbytes <= 0)
return 0;
@ -563,7 +617,11 @@ inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes)
Assert(buf != NULL);
/* enforce writability because snapshot is probably wrong otherwise */
Assert(obj_desc->flags & IFS_WRLOCK);
if ((obj_desc->flags & IFS_WRLOCK) == 0)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
obj_desc->id)));
if (nbytes <= 0)
return 0;
@ -749,7 +807,11 @@ inv_truncate(LargeObjectDesc *obj_desc, int64 len)
Assert(PointerIsValid(obj_desc));
/* enforce writability because snapshot is probably wrong otherwise */
Assert(obj_desc->flags & IFS_WRLOCK);
if ((obj_desc->flags & IFS_WRLOCK) == 0)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for large object %u",
obj_desc->id)));
/*
* use errmsg_internal here because we don't want to expose INT64_FORMAT

12
src/backend/utils/misc/guc.c
View File

@ -43,7 +43,6 @@
#include "commands/trigger.h"
#include "funcapi.h"
#include "libpq/auth.h"
#include "libpq/be-fsstubs.h"
#include "libpq/libpq.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
@ -71,6 +70,7 @@
#include "storage/dsm_impl.h"
#include "storage/standby.h"
#include "storage/fd.h"
#include "storage/large_object.h"
#include "storage/pg_shmem.h"
#include "storage/proc.h"
#include "storage/predicate.h"
@ -4900,7 +4900,7 @@ ResetAllOptions(void)
if (conf->assign_hook)
conf->assign_hook(conf->reset_val,
conf->reset_extra);
conf->reset_extra);
*conf->variable = conf->reset_val;
set_extra_field(&conf->gen, &conf->gen.extra,
conf->reset_extra);
@ -4912,7 +4912,7 @@ ResetAllOptions(void)
if (conf->assign_hook)
conf->assign_hook(conf->reset_val,
conf->reset_extra);
conf->reset_extra);
*conf->variable = conf->reset_val;
set_extra_field(&conf->gen, &conf->gen.extra,
conf->reset_extra);
@ -4924,7 +4924,7 @@ ResetAllOptions(void)
if (conf->assign_hook)
conf->assign_hook(conf->reset_val,
conf->reset_extra);
conf->reset_extra);
*conf->variable = conf->reset_val;
set_extra_field(&conf->gen, &conf->gen.extra,
conf->reset_extra);
@ -4936,7 +4936,7 @@ ResetAllOptions(void)
if (conf->assign_hook)
conf->assign_hook(conf->reset_val,
conf->reset_extra);
conf->reset_extra);
set_string_field(conf, conf->variable, conf->reset_val);
set_extra_field(&conf->gen, &conf->gen.extra,
conf->reset_extra);
@ -4948,7 +4948,7 @@ ResetAllOptions(void)
if (conf->assign_hook)
conf->assign_hook(conf->reset_val,
conf->reset_extra);
conf->reset_extra);
*conf->variable = conf->reset_val;
set_extra_field(&conf->gen, &conf->gen.extra,
conf->reset_extra);

5
src/include/libpq/be-fsstubs.h
View File

@ -14,11 +14,6 @@
#ifndef BE_FSSTUBS_H
#define BE_FSSTUBS_H
/*
* compatibility option for access control
*/
extern bool lo_compat_privileges;
/*
* These are not fmgr-callable, but are available to C code.
* Probably these should have had the underscore-free names,

13
src/include/storage/large_object.h
View File

@ -27,9 +27,9 @@
* offset is the current seek offset within the LO
* flags contains some flag bits
*
* NOTE: in current usage, flag bit IFS_RDLOCK is *always* set, and we don't
* bother to test for it. Permission checks are made at first read or write
* attempt, not during inv_open(), so we have other bits to remember that.
* NOTE: as of v11, permission checks are made when the large object is
* opened; therefore IFS_RDLOCK/IFS_WRLOCK indicate that read or write mode
* has been requested *and* the corresponding permission has been checked.
*
* NOTE: before 7.1, we also had to store references to the separate table
* and index of a specific large object. Now they all live in pg_largeobject
@ -47,8 +47,6 @@ typedef struct LargeObjectDesc
/* bits in flags: */
#define IFS_RDLOCK (1 << 0) /* LO was opened for reading */
#define IFS_WRLOCK (1 << 1) /* LO was opened for writing */
#define IFS_RD_PERM_OK (1 << 2) /* read permission has been verified */
#define IFS_WR_PERM_OK (1 << 3) /* write permission has been verified */
} LargeObjectDesc;
@ -78,6 +76,11 @@ typedef struct LargeObjectDesc
#define MAX_LARGE_OBJECT_SIZE ((int64) INT_MAX * LOBLKSIZE)
/*
* GUC: backwards-compatibility flag to suppress LO permission checks
*/
extern bool lo_compat_privileges;
/*
* Function definitions...
*/