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error on no forward progress

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streaming decoders, such as ZSTD_decompressStream() or ZSTD_decompress_generic(),
may end up making no forward progress,
(aka no byte read from input __and__ no byte written to output),
due to unusual parameters conditions,
such as providing an output buffer already full.

In such case, the caller may be caught in an infinite loop,
calling the streaming decompression function again and again,
without making any progress.

This version detects such situation, and generates an error instead :
ZSTD_error_dstSize_tooSmall when output buffer is full,
ZSTD_error_srcSize_wrong when input buffer is empty.

The detection tolerates a number of attempts before triggering an error,
controlled by ZSTD_NO_FORWARD_PROGRESS_MAX macro constant,
which is set to 16 by default, and can be re-defined at compilation time.
This behavior tolerates potentially existing implementations
where such cases happen sporadically, like once or twice,
which is not dangerous (only infinite loops are),
without generating an error, hence without breaking these implementations.
This commit is contained in:
Yann Collet
2018-06-22 17:58:21 -07:00
parent 3934e010a2
commit 31769ce702
3 changed files with 61 additions and 5 deletions
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lib/decompress/zstd_decompress.c
+26 -2
View File
@@ -41,6 +41,17 @@
#endif
/*!
* NO_FORWARD_PROGRESS_MAX :
* maximum allowed nb of calls to ZSTD_decompressStream() and ZSTD_decompress_generic()
* without any forward progress
* (defined as: no byte read from input, and no byte flushed to output)
* before triggering an error.
*/
#ifndef ZSTD_NO_FORWARD_PROGRESS_MAX
# define ZSTD_NO_FORWARD_PROGRESS_MAX 16
#endif
/*-*******************************************************
* Dependencies
*********************************************************/
@@ -153,6 +164,7 @@ struct ZSTD_DCtx_s
U32 previousLegacyVersion;
U32 legacyVersion;
U32 hostageByte;
int noForwardProgress;
/* workspace */
BYTE litBuffer[ZSTD_BLOCKSIZE_MAX + WILDCOPY_OVERLENGTH];
@@ -194,6 +206,7 @@ static void ZSTD_initDCtx_internal(ZSTD_DCtx* dctx)
dctx->streamStage = zdss_init;
dctx->legacyContext = NULL;
dctx->previousLegacyVersion = 0;
dctx->noForwardProgress = 0;
dctx->bmi2 = ZSTD_cpuid_bmi2(ZSTD_cpuid());
}
@@ -2620,6 +2633,7 @@ size_t ZSTD_initDStream_usingDict(ZSTD_DStream* zds, const void* dict, size_t di
{
DEBUGLOG(4, "ZSTD_initDStream_usingDict");
zds->streamStage = zdss_init;
zds->noForwardProgress = 0;
CHECK_F( ZSTD_DCtx_loadDictionary(zds, dict, dictSize) );
return ZSTD_frameHeaderSize_prefix;
}
@@ -2960,8 +2974,18 @@ size_t ZSTD_decompressStream(ZSTD_DStream* zds, ZSTD_outBuffer* output, ZSTD_inB
} }
/* result */
input->pos += (size_t)(ip-istart);
output->pos += (size_t)(op-ostart);
input->pos = (size_t)(ip - (const char*)(input->src));
output->pos = (size_t)(op - (char*)(output->dst));
if ((ip==istart) && (op==ostart)) { /* no forward progress */
zds->noForwardProgress ++;
if (zds->noForwardProgress >= ZSTD_NO_FORWARD_PROGRESS_MAX) {
if (op==oend) return ERROR(dstSize_tooSmall);
if (ip==iend) return ERROR(srcSize_wrong);
assert(0);
}
} else {
zds->noForwardProgress = 0;
}
{ size_t nextSrcSizeHint = ZSTD_nextSrcSizeToDecompress(zds);
if (!nextSrcSizeHint) { /* frame fully decoded */
if (zds->outEnd == zds->outStart) { /* output fully flushed */