Messages in this thread | | | Date | Mon, 24 Oct 2022 19:49:17 +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 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.
> > > > > 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>
Thanks!
Dave
> -- > 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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