Messages in this thread | | | Date | Sat, 29 Oct 2022 13:48:05 +0100 | From | "Dr. David Alan Gilbert" <> | Subject | Re: [PATCH] jfs: Fix fortify moan in symlink |
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* Kees Cook (keescook@chromium.org) wrote: > On Mon, Oct 24, 2022 at 07:49:17PM +0100, Dr. David Alan Gilbert wrote: > > * Kees Cook (keescook@chromium.org) wrote: > > > On Sat, Oct 22, 2022 at 09:39:14PM +0100, linux@treblig.org wrote: > > > > From: "Dr. David Alan Gilbert" <linux@treblig.org> > > > > > > > > JFS has in jfs_incore.h: > > > > > > > > /* _inline may overflow into _inline_ea when needed */ > > > > /* _inline_ea may overlay the last part of > > > > * file._xtroot if maxentry = XTROOTINITSLOT > > > > */ > > > > union { > > > > struct { > > > > /* 128: inline symlink */ > > > > unchar _inline[128]; > > > > /* 128: inline extended attr */ > > > > unchar _inline_ea[128]; > > > > }; > > > > unchar _inline_all[256]; > > > > > > > > and currently the symlink code copies into _inline; > > > > if this is larger than 128 bytes it triggers a fortify warning of the > > > > form: > > > > > > > > memcpy: detected field-spanning write (size 132) of single field > > > > "ip->i_link" at fs/jfs/namei.c:950 (size 18446744073709551615) > > > > > > Which compiler are you using for this build? > > > > I think that report was the same on gcc on Fedora 37 and whatever > > syzkaller was running. > > > > > This size report (SIZE_MAX) > > > should be impossible to reach. But also, the size is just wrong -- > > > i_inline is 128 bytes, not SIZE_MAX. So, the detection is working > > > (132 > 128), but the report is broken, and I can't see how... > > > > Yeh, and led me down a blind alley for a while thinking something had > > really managed to screwup the strlen somehow. > > This looks like a GCC bug (going at least back to GCC 10.2)[1], but some > extra care around the macro appears to make it go away, so the reporting > variable doesn't get confused/re-evaluated:
Thanks for chasing that; are you also going to file a gcc bug?
Dave
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h > index 09a032f6ce6b..9e2d96993c30 100644 > --- a/include/linux/fortify-string.h > +++ b/include/linux/fortify-string.h > @@ -550,13 +550,18 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size, > > #define __fortify_memcpy_chk(p, q, size, p_size, q_size, \ > p_size_field, q_size_field, op) ({ \ > - size_t __fortify_size = (size_t)(size); \ > - WARN_ONCE(fortify_memcpy_chk(__fortify_size, p_size, q_size, \ > - p_size_field, q_size_field, #op), \ > + const size_t __fortify_size = (size_t)(size); \ > + const size_t __p_size = (p_size); \ > + const size_t __q_size = (q_size); \ > + const size_t __p_size_field = (p_size_field); \ > + const size_t __q_size_field = (q_size_field); \ > + WARN_ONCE(fortify_memcpy_chk(__fortify_size, __p_size, \ > + __q_size, __p_size_field, \ > + __q_size_field, #op), \ > #op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \ > __fortify_size, \ > "field \"" #p "\" at " __FILE__ ":" __stringify(__LINE__), \ > - p_size_field); \ > + __p_size_field); \ > __underlying_##op(p, q, __fortify_size); \ > }) > > > > [1] https://syzkaller.appspot.com/bug?id=23d613df5259b977dac1696bec77f61a85890e3d > > -- > Kees Cook -- -----Open up your eyes, open up your mind, open up your code ------- / Dr. David Alan Gilbert | Running GNU/Linux | Happy \ \ dave @ treblig.org | | In Hex / \ _________________________|_____ http://www.treblig.org |_______/
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