> On Oct 9, 2023, at 1:29 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > !-------------------------------------------------------------------| > This Message Is From an External Sender > > |-------------------------------------------------------------------! > > 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; Thanks Eric and Kees for the report and the fix! I am working on putting this patch up now, just need to test the fix myself to ensure I can reproduce the issue and the fix. In your opinion does this worth trying to get this patch into v6.6, or should it wait for v6.7? Best, Nick Terrell > 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
