Messages in this thread Patch in this message | | | Date | Mon, 24 Oct 2022 10:28:27 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] jfs: Fix fortify moan in symlink |
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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? 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...
> > when it's actually OK. > > Copy it into _inline_all instead. > > Reported-by: syzbot+5fc38b2ddbbca7f5c680@syzkaller.appspotmail.com > Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org> > --- > fs/jfs/namei.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/jfs/namei.c b/fs/jfs/namei.c > index 9db4f5789c0ec..4fbbf88435e69 100644 > --- a/fs/jfs/namei.c > +++ b/fs/jfs/namei.c > @@ -946,7 +946,7 @@ static int jfs_symlink(struct user_namespace *mnt_userns, struct inode *dip, > if (ssize <= IDATASIZE) { > ip->i_op = &jfs_fast_symlink_inode_operations; > > - ip->i_link = JFS_IP(ip)->i_inline; > + ip->i_link = JFS_IP(ip)->i_inline_all; > memcpy(ip->i_link, name, ssize); > ip->i_size = ssize - 1; >
Regardless, the fix looks correct to me!
Reviewed-by: Kees Cook <keescook@chromium.org>
-- Kees Cook
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