[IMA] Re: possible deadlock in get_user_pages_unlocked (2)

[Eric Biggers]

On Tue, Jun 04, 2019 at 06:16:00PM -0700, syzbot wrote:
> syzbot has bisected this bug to:
> 
> commit 69d61f577d147b396be0991b2ac6f65057f7d445
> Author: Mimi Zohar <zohar at linux.ibm.com>
> Date:   Wed Apr 3 21:47:46 2019 +0000
> 
>     ima: verify mprotect change is consistent with mmap policy
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1055a2f2a00000
> start commit:   56b697c6 Add linux-next specific files for 20190604
> git tree:       linux-next
> final crash:    https://syzkaller.appspot.com/x/report.txt?x=1255a2f2a00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1455a2f2a00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4248d6bc70076f7d
> dashboard link: https://syzkaller.appspot.com/bug?extid=e1374b2ec8f6a25ab2e5
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=165757eea00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10dd3e86a00000
> 
> Reported-by: syzbot+e1374b2ec8f6a25ab2e5 at syzkaller.appspotmail.com
> Fixes: 69d61f577d14 ("ima: verify mprotect change is consistent with mmap
> policy")
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> 

Hi Mimi, it seems your change to call ima_file_mmap() from
security_file_mprotect() violates the locking order by taking i_rwsem while
mmap_sem is held.

- Eric