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fix out-of-bound read within LZ4_decompress_fast()

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and deprecate LZ4_decompress_fast(),
with deprecation warnings enabled by default.

Note that, as a consequence of the fix,
LZ4_decompress_fast is now __slower__ than LZ4_decompress_safe().
That's because, since it doesn't know the input buffer size,
it must progress more cautiously into the input buffer
to ensure to out-of-bound read.
This commit is contained in:
Yann Collet 2019-04-17 15:01:53 -07:00
parent 1ed69691a1
commit 25d96f1e4d
2 changed files with 23 additions and 11 deletions
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15
lib/lz4.c
View File

@ -135,6 +135,9 @@
# endif /* _MSC_VER */
#endif /* LZ4_FORCE_INLINE */
#undef LZ4_FORCE_INLINE
#define LZ4_FORCE_INLINE static /* disable */
/* LZ4_FORCE_O2_GCC_PPC64LE and LZ4_FORCE_O2_INLINE_GCC_PPC64LE
* Gcc on ppc64le generates an unrolled SIMDized loop for LZ4_wildCopy,
* together with a simple 8-byte copy loop as a fall-back path.
@ -1671,7 +1674,10 @@ LZ4_decompress_generic(
{
goto safe_literal_copy;
}
LZ4_wildCopy32(op, ip, cpy);
if (endOnInput)
LZ4_wildCopy32(op, ip, cpy);
else
LZ4_wildCopy(op, ip, cpy); /* LZ4_decompress_fast() cannot copy more than 8 bytes at a time : it doesn't know input length, and only relies on end-of-block properties */
ip += length; op = cpy;
} else {
cpy = op+length;
@ -1681,7 +1687,12 @@ LZ4_decompress_generic(
goto safe_literal_copy;
}
/* Literals can only be 14, but hope compilers optimize if we copy by a register size */
memcpy(op, ip, 16);
if (endOnInput)
memcpy(op, ip, 16);
else { /* LZ4_decompress_fast() cannot copy more than 8 bytes at a time : it doesn't know input length, and only relies on end-of-block properties */
memcpy(op, ip, 8);
if (length > 8) memcpy(op+8, ip+8, 8);
}
ip += length; op = cpy;
}

19
lib/lz4.h
View File

@ -631,14 +631,15 @@ LZ4_DEPRECATED("use LZ4_decompress_safe_usingDict() instead") LZ4LIB_API int LZ4
LZ4_DEPRECATED("use LZ4_decompress_fast_usingDict() instead") LZ4LIB_API int LZ4_decompress_fast_withPrefix64k (const char* src, char* dst, int originalSize);
/*! LZ4_decompress_fast() : **unsafe!**
* These functions are generally slightly faster than LZ4_decompress_safe(),
* though the difference is small (generally ~5%).
* However, the real cost is a risk : LZ4_decompress_safe() is protected vs malformed input, while `LZ4_decompress_fast()` is not, making it a security liability.
* These functions used to be faster than LZ4_decompress_safe(),
* but it has changed, and they are now slower than LZ4_decompress_safe().
* This is because LZ4_decompress_fast() doesn't know the input size,
* and therefore must progress more cautiously in the input buffer to not read beyond the end of block.
* On top of that `LZ4_decompress_fast()` is not protected vs malformed or malicious inputs, making it a security liability.
* As a consequence, LZ4_decompress_fast() is strongly discouraged, and deprecated.
* These functions will generate a deprecation warning in the future.
*
* Last LZ4_decompress_fast() specificity is that it can decompress a block without knowing its compressed size.
* Note that even that functionality could be achieved in a more secure manner if need be,
* Only LZ4_decompress_fast() specificity is that it can decompress a block without knowing its compressed size.
* Even that functionality could be achieved in a more secure manner if need be,
* though it would require new prototypes, and adaptation of the implementation to this new use case.
*
* Parameters:
@ -655,11 +656,11 @@ LZ4_DEPRECATED("use LZ4_decompress_fast_usingDict() instead") LZ4LIB_API int LZ4
* As a consequence, use these functions in trusted environments with trusted data **only**.
*/
/* LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe() instead") */
LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe() instead")
LZ4LIB_API int LZ4_decompress_fast (const char* src, char* dst, int originalSize);
/* LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_continue() instead") */
LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_continue() instead")
LZ4LIB_API int LZ4_decompress_fast_continue (LZ4_streamDecode_t* LZ4_streamDecode, const char* src, char* dst, int originalSize);
/* LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_usingDict() instead") */
LZ4_DEPRECATED("This function is deprecated and unsafe. Consider using LZ4_decompress_safe_usingDict() instead")
LZ4LIB_API int LZ4_decompress_fast_usingDict (const char* src, char* dst, int originalSize, const char* dictStart, int dictSize);
/*! LZ4_resetStream() :