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
