Messages in this thread Patch in this message | | | Date | Fri, 13 Jan 2023 19:15:12 -0800 | From | Kees Cook <> | Subject | Re: [PATCH v2] lib: zstd: Fix -Wstringop-overflow warning |
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On Sat, Jan 14, 2023 at 01:06:07AM +0000, Nick Terrell wrote: > > > > On Jan 13, 2023, at 4:48 PM, Kees Cook <keescook@chromium.org> wrote: > > > > !-------------------------------------------------------------------| > > This Message Is From an External Sender > > > > |-------------------------------------------------------------------! > > > > On Tue, Jan 10, 2023 at 11:10:08PM +0000, Nick Terrell wrote: > >> > >> > >>> On Jan 4, 2023, at 1:20 PM, Kees Cook <keescook@chromium.org> wrote: > >>> > >>> !-------------------------------------------------------------------| > >>> This Message Is From an External Sender > >>> > >>> |-------------------------------------------------------------------! > >>> > >>> Fix the following -Wstringop-overflow warning when building with GCC 11+: > >>> > >>> lib/zstd/decompress/huf_decompress.c: In function ‘HUF_readDTableX2_wksp’: > >>> lib/zstd/decompress/huf_decompress.c:700:5: warning: ‘HUF_fillDTableX2.constprop’ accessing 624 bytes in a region of size 52 [-Wstringop-overflow=] > >>> 700 | HUF_fillDTableX2(dt, maxTableLog, > >>> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> 701 | wksp->sortedSymbol, sizeOfSort, > >>> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> 702 | wksp->rankStart0, wksp->rankVal, maxW, > >>> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> 703 | tableLog+1, > >>> | ~~~~~~~~~~~ > >>> 704 | wksp->calleeWksp, sizeof(wksp->calleeWksp) / sizeof(U32)); > >>> | > >>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> lib/zstd/decompress/huf_decompress.c:700:5: note: referencing argument 6 of type ‘U32 (*)[13]’ {aka ‘unsigned int (*)[13]’} > >>> lib/zstd/decompress/huf_decompress.c:571:13: note: in a call to function ‘HUF_fillDTableX2.constprop’ > >>> 571 | static void HUF_fillDTableX2(HUF_DEltX2* DTable, const U32 targetLog, > >>> | ^~~~~~~~~~~~~~~~ > >>> > >>> by using pointer notation instead of array notation. > >>> > >>> This is one of the last remaining warnings to be fixed before globally > >>> enabling -Wstringop-overflow. > >> > >> The patch looks correct to me, thanks for reviving it. But, I was attempting to reproduce the issue, > >> so I could better understand what's going on, and I wasn't able to reproduce it myself. > >> > >> To attempt to reproduce, I applied this patch > >> > >> --- > >> diff --git a/lib/zstd/Makefile b/lib/zstd/Makefile > >> index 20f08c644b71..190d3d5ab4be 100644 > >> --- a/lib/zstd/Makefile > >> +++ b/lib/zstd/Makefile > >> @@ -12,6 +12,8 @@ obj-$(CONFIG_ZSTD_COMPRESS) += zstd_compress.o > >> obj-$(CONFIG_ZSTD_DECOMPRESS) += zstd_decompress.o > >> obj-$(CONFIG_ZSTD_COMMON) += zstd_common.o > >> > >> +ccflags-y := -Wstringop-overflow=4 -Werror > >> + > >> zstd_compress-y := \ > >> zstd_compress_module.o \ > >> compress/fse_compress.o \ > >> --- > >> > >> Then compiled on x86-64 with gcc 12.2.0 on tag v6.2-rc3. I saw no errors. > >> I also tried with just `-Wstringop-overflow`, and on upstream zstd. I tried to > >> make a minimal reproducer on godbolt, so I could see if it was the gcc version, > >> but wasn't able to make it fail with any of them https://gcc.godbolt.org/z/Exzq9arMr . > >> > >> Could you please tell me how to reproduce this warning? > > > > I saw it like so with next-20230113 on x86_64: > > > > $ gcc --version > > gcc (Ubuntu 12.2.0-3ubuntu1) 12.2.0 > > ... > > $ make KCFLAGS=-Wstringop-overflow allmodconfig lib/zstd/decompress/huf_decompress.o > > Thanks, I was able to repro it! I will merge this patch into my tree.
Thanks!
> If you would like to submit the same patch upstream yourself, I will accept the PR, otherwise I can submit an upstream PR.
I don't know the process there, so if you could do it, I'd appreciate it.
> Just to be certain, this patch is to work around a shortcoming in > -Wstringop-overflow, but the code was otherwise correct?
It's the same result for the binary output. The types indicated in the function prototype meant there was cross-struct-member overflow (i.e. writing to the second array dimension when only 1 was specified), but the way to clear up intention isn't as clean here, so I'd kind of say half a code correctness issue, and half a work-around. *makes wavey hands gesture*
-Kees -- Kees Cook
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