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Message-ID: <19E42116-8FE3-4C4B-8D26-E9B47B0B9AC5@meta.com> Date: Thu, 12 Oct 2023 19:55:55 +0000 From: Nick Terrell <terrelln@...a.com> To: Kees Cook <keescook@...omium.org> CC: Nick Terrell <terrelln@...a.com>, Eric Biggers <ebiggers@...nel.org>, Nick Terrell <terrelln@...a.com>, syzbot <syzbot+1f2eb3e8cd123ffce499@...kaller.appspotmail.com>, Chris Mason <clm@...a.com>, "dsterba@...e.com" <dsterba@...e.com>, "josef@...icpanda.com" <josef@...icpanda.com>, "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>, "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org> Subject: Re: [syzbot] [zstd] UBSAN: array-index-out-of-bounds in FSE_decompress_wksp_body_bmi2 > On Oct 9, 2023, at 1:29 PM, Kees Cook <keescook@...omium.org> 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
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