Re: [syzbot] [ntfs?] WARNING in do_open_execat

[Matthew Wilcox]

On Fri, Aug 18, 2023 at 10:33:26AM -0700, Kees Cook wrote:
> On Fri, Aug 18, 2023 at 11:26:51AM -0500, Eric W. Biederman wrote:
> > syzbot <syzbot+6ec38f7a8db3b3fb1002@xxxxxxxxxxxxxxxxxxxxxxxxx> writes:
> > 
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > 
> > Not an issue.
> > Nothing to do with ntfs.
> > 
> > The code is working as designed and intended.
> > 
> > syzbot generated a malformed exec and the kernel made it
> > well formed and warned about it.
> > 
> > Human beings who run syzbot please mark this as not an issue in your
> > system.  The directions don't have a way to say that the code is working
> > as expected and designed.
> 
> WARN and BUG should not be reachable from userspace, so if this can be
> tripped we should take a closer look and likely fix it...
> 
> > > HEAD commit:    16931859a650 Merge tag 'nfsd-6.5-4' of git://git.kernel.or..
> > > git tree:       upstream
> > > console+strace: https://syzkaller.appspot.com/x/log.txt?x=13e2673da80000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=aa796b6080b04102
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=6ec38f7a8db3b3fb1002
> > > compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17cdbc65a80000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1262d8cfa80000
> > >
> > > Downloadable assets:
> > > disk image: https://storage.googleapis.com/syzbot-assets/eecc010800b4/disk-16931859.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/f45ae06377a7/vmlinux-16931859.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/68891896edba/bzImage-16931859.xz
> > > mounted in repro: https://storage.googleapis.com/syzbot-assets/4b6ab78b223a/mount_0.gz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+6ec38f7a8db3b3fb1002@xxxxxxxxxxxxxxxxxxxxxxxxx
> > >
> > > ntfs: volume version 3.1.
> > > process 'syz-executor300' launched './file1' with NULL argv: empty string added
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 5020 at fs/exec.c:933 do_open_execat+0x18f/0x3f0 fs/exec.c:933
> 
> This is a double-check I left in place, since it shouldn't have been reachable:
> 
>         /*
>          * may_open() has already checked for this, so it should be
>          * impossible to trip now. But we need to be extra cautious
>          * and check again at the very end too.
>          */
>         err = -EACCES;
>         if (WARN_ON_ONCE(!S_ISREG(file_inode(file)->i_mode) ||
>                          path_noexec(&file->f_path)))
>                 goto exit;
> 
> So yes, let's figure this out...

When trying to figure it out, remember that ntfs corrupts random memory,
so all reports from syzbot that have "ntfs" in them should be discarded.
I tried to tell them that all this work they're doing testing ntfs3 is
pointless, but they won't listen.