On Sat, Oct 07, 2023 at 02:05:56PM -0700, Eric Biggers wrote:
> Hi Nick,
>
> On Wed, Aug 30, 2023 at 12:49:53AM -0700, syzbot wrote:
> > UBSAN: array-index-out-of-bounds in lib/zstd/common/fse_decompress.c:345:30
> > index 33 is out of range for type 'FSE_DTable[1]' (aka 'unsigned int[1]')
>
> Zstandard needs to be converted to use C99 flex-arrays instead of length-1
> arrays. https://github.com/facebook/zstd/pull/3785 would fix this in upstream
> Zstandard, though it doesn't work well with the fact that upstream Zstandard
> supports C90. Not sure how you want to handle this.
For the kernel, we just need:
diff --git a/lib/zstd/common/fse_decompress.c b/lib/zstd/common/fse_decompress.c
index a0d06095be83..b11e87fff261 100644
--- a/lib/zstd/common/fse_decompress.c
+++ b/lib/zstd/common/fse_decompress.c
@@ -312,7 +312,7 @@ size_t FSE_decompress_wksp(void* dst, size_t dstCapacity,
const void* cSrc, size
typedef struct {
short ncount[FSE_MAX_SYMBOL_VALUE + 1];
- FSE_DTable dtable[1]; /* Dynamically sized */
+ FSE_DTable dtable[]; /* Dynamically sized */
} FSE_DecompressWksp;
And if upstream wants to stay C89 compat, perhaps:
#if __STDC_VERSION__ >= 199901L
# define __FLEX_ARRAY_DIM /*C99*/
#else
# define __FLEX_ARRAY_DIM 0
#endif
and then use __FLEX_ARRAY_DIM as needed (and keep the other "-1" changes
in the github commit):
typedef struct {
short ncount[FSE_MAX_SYMBOL_VALUE + 1];
- FSE_DTable dtable[1]; /* Dynamically sized */
+ FSE_DTable dtable[__FLEX_ARRAY_DIM]; /* Dynamically sized */
} FSE_DecompressWksp;
--
Kees Cook
