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Fixed buffer over-read at the boundary. 

- Say we are using a lock size of 1024k, we send a request for 128k at 1008k. It won't trigger the download, because we already download 1024k at 0. So it would read off from the empty disk space!
- This problem only occurs during the first time you download a file. During subsequent accesses, when you are only reading from the cache, this problem does not occur.
This commit is contained in:
Fufu Fang 2019-09-02 15:19:41 +01:00
parent 9e3e4747ae
commit 6c8a15d8cc
No known key found for this signature in database
GPG Key ID: 0F6BB5EF6F8BB729
2 changed files with 15 additions and 17 deletions
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28
src/cache.c
View File

@ -948,14 +948,16 @@ static void *Cache_bgdl(void *arg)
}
long Cache_read(Cache *cf, char * const output_buf, const off_t len,
const off_t offset)
const off_t offset_start)
{
long send;
off_t dl_offset = offset / cf->blksz * cf->blksz;
/* The offset of the segment to be downloaded */
off_t dl_offset = (offset_start + len) / cf->blksz * cf->blksz;
/* ------------------ Check if the segment already exists ---------------*/
if (Seg_exist(cf, offset)) {
send = Data_read(cf, (uint8_t *) output_buf, len, offset);
if (Seg_exist(cf, dl_offset)) {
send = Data_read(cf, (uint8_t *) output_buf, len, offset_start);
goto bgdl;
} else {
/* Wait for any other download thread to finish*/
@ -964,10 +966,10 @@ long Cache_read(Cache *cf, char * const output_buf, const off_t len,
pthread_self());
#endif
PTHREAD_MUTEX_LOCK(&cf->w_lock);
if (Seg_exist(cf, offset)) {
if (Seg_exist(cf, dl_offset)) {
/* The segment now exists - it was downloaded by another
* download thread. Send it off and unlock the I/O */
send = Data_read(cf, (uint8_t *) output_buf, len, offset);
send = Data_read(cf, (uint8_t *) output_buf, len, offset_start);
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_read(): thread %lu: unlocking w_lock;\n",
pthread_self());
@ -983,13 +985,6 @@ long Cache_read(Cache *cf, char * const output_buf, const off_t len,
fprintf(stderr, "Cache_read(): thread %lu: ", pthread_self());
long recv = path_download(cf->path, (char *) recv_buf, cf->blksz,
dl_offset);
if (recv < len) {
send = recv;
} else {
send = len;
}
memmove(output_buf, recv_buf + (offset - dl_offset), send);
/*
* check if we have received enough data, write it to the disk
*
@ -1006,6 +1001,7 @@ long Cache_read(Cache *cf, char * const output_buf, const off_t len,
"Cache_read(): received %ld, possible network error.\n", recv);
}
free(recv_buf);
send = Data_read(cf, (uint8_t *) output_buf, len, offset_start);
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_read(): thread %lu: unlocking w_lock;\n",
@ -1015,7 +1011,9 @@ long Cache_read(Cache *cf, char * const output_buf, const off_t len,
/* -----------Download the next segment in background -------------------*/
bgdl:
if ( (cf->next_offset > dl_offset) &&
;
off_t next_offset = round_div(offset_start, cf->blksz) * cf->blksz;
if ( (next_offset > dl_offset) &&
!Seg_exist(cf, cf->next_offset) &&
cf->next_offset < cf->content_length ){
/* Stop the spawning of multiple background pthreads */
@ -1024,7 +1022,7 @@ long Cache_read(Cache *cf, char * const output_buf, const off_t len,
fprintf(stderr, "Cache_read(): thread %lu: trylocked bgt_lock;\n",
pthread_self());
#endif
cf->next_offset = round_div(offset, cf->blksz) * cf->blksz;
cf->next_offset = next_offset;
if (pthread_create(&cf->bgt, NULL, Cache_bgdl, cf)) {
fprintf(stderr,
"Cache_read(): Error creating background download thread\n"

4
src/cache.h
View File

@ -136,10 +136,10 @@ void Cache_delete(const char *fn);
* \param[in] cf the cache in-memory data structure
* \param[out] output_buf the output buffer
* \param[in] len the requested segment size
* \param[in] offset the start of the segment
* \param[in] offset_start the start of the segment
* \return the length of the segment the cache system managed to obtain.
* \note Called by fs_read(), verified to be working
*/
long Cache_read(Cache *cf, char * const output_buf, const off_t len,
const off_t offset);
const off_t offset_start);
#endif