Messages in this thread | | | Date | Tue, 18 Jul 2023 22:00:24 -0700 | From | Kees Cook <> | Subject | Re: [PATCH v1 1/1] seq_file: Replace strncpy()+nul by strscpy() |
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On Mon, Jul 17, 2023 at 04:09:23PM -0700, Kees Cook wrote: > > On Mon, 17 Jul 2023 12:33:32 +0300, Andy Shevchenko wrote: > > Privided seq_show_option_n() macro breaks build with -Werror > > and W=1, e.g.: > > > > In function ‘strncpy’, > > inlined from ‘ocfs2_show_options’ at fs/ocfs2/super.c:1520:3: > > include/linux/fortify-string.h:68:33: error: ‘__builtin_strncpy’ output may be truncated copying 4 bytes from a string of length 4 [-Werror=stringop-truncation] > > 68 | #define __underlying_strncpy __builtin_strncpy > > | ^ > > include/linux/fortify-string.h:151:16: note: in expansion of macro ‘__underlying_strncpy’ > > 151 | return __underlying_strncpy(p, q, size); > > | ^~~~~~~~~~~~~~~~~~~~ > > cc1: all warnings being treated as errors > > > > [...] > > Applied, thanks! > > [1/1] seq_file: Replace strncpy()+nul by strscpy() > https://git.kernel.org/kees/c/c30417b20f49
Gah, I dropped this from my tree since it was actually wrong[1]. This is an ugly corner case with strscpy vs strncpy: the cast be32 from hfs/hfsplus[2] looks unterminated to strscpy, so it would return -E2BIG, but really FORTIFY noticed the over-read (strscpy is correctly checking the 5th byte for NUL).
So... I think we need to fix seq_show_option_n() using memcpy+NUL, drop the ocfs2 usage, and clarify that the seq_show_option_n() docs mean "n means _exactly_ n bytes"...
-Kees
[1] https://lore.kernel.org/lkml/0000000000000a88cb0600ccef54@google.com/ [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/hfsplus/options.c?h=v6.4#n221
-- Kees Cook
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