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Date: Wed, 15 May 2024 17:12:56 +0200
From: =?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?= <mic@digikod.net>
To: Paul Moore <paul@paul-moore.com>, Jann Horn <jannh@google.com>
Cc: syzbot <syzbot+5446fbf332b0602ede0b@syzkaller.appspotmail.com>, 
	jmorris@namei.org, linux-kernel@vger.kernel.org, 
	linux-security-module@vger.kernel.org, serge@hallyn.com, syzkaller-bugs@googlegroups.com, 
	linux-fsdevel@vger.kernel.org, Casey Schaufler <casey@schaufler-ca.com>, 
	Christian Brauner <brauner@kernel.org>
Subject: Re: [syzbot] [lsm?] general protection fault in
 hook_inode_free_security
Message-ID: <20240515.Yoo5chaiNai9@digikod.net>
References: <00000000000076ba3b0617f65cc8@google.com>
 <CAHC9VhSmbAY8gX=Mh2OT-dkQt+W3xaa9q9LVWkP9q8pnMh+E_w@mail.gmail.com>
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On Thu, May 09, 2024 at 08:01:49PM -0400, Paul Moore wrote:
> On Wed, May 8, 2024 at 3:32 PM syzbot
> <syzbot+5446fbf332b0602ede0b@syzkaller.appspotmail.com> wrote:
> >
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    dccb07f2914c Merge tag 'for-6.9-rc7-tag' of git://git.kern..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=14a46760980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=6d14c12b661fb43
> > dashboard link: https://syzkaller.appspot.com/bug?extid=5446fbf332b0602ede0b
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/39d66018d8ad/disk-dccb07f2.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/c160b651d1bc/vmlinux-dccb07f2.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/3662a33ac713/bzImage-dccb07f2.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+5446fbf332b0602ede0b@syzkaller.appspotmail.com
> >
> > general protection fault, probably for non-canonical address 0xdffffc018f62f515: 0000 [#1] PREEMPT SMP KASAN NOPTI
> > KASAN: probably user-memory-access in range [0x0000000c7b17a8a8-0x0000000c7b17a8af]
> > CPU: 1 PID: 5102 Comm: syz-executor.1 Not tainted 6.9.0-rc7-syzkaller-00012-gdccb07f2914c #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
> > RIP: 0010:hook_inode_free_security+0x5b/0xb0 security/landlock/fs.c:1047
> 
> Possibly a Landlock issue, Mickaël?

It looks like security_inode_free() is called two times on the same
inode.  This could happen if an inode labeled by Landlock is put
concurrently with release_inode() for a closed ruleset or with
hook_sb_delete().  I didn't find any race condition that could lead to
two calls to iput() though.  Could WRITE_ONCE(object->underobj, NULL)
change anything even if object->lock is locked?

A bit unrelated but looking at the SELinux code, I see that selinux_inode()
checks `!inode->i_security`.  In which case could this happen?

> 
> > Code: 8a fd 48 8b 1b 48 c7 c0 c4 4e d5 8d 48 c1 e8 03 42 0f b6 04 30 84 c0 75 3e 48 63 05 33 59 65 09 48 01 c3 48 89 d8 48 c1 e8 03 <42> 80 3c 30 00 74 08 48 89 df e8 66 be 8a fd 48 83 3b 00 75 0d e8
> > RSP: 0018:ffffc9000307f9a8 EFLAGS: 00010212
> > RAX: 000000018f62f515 RBX: 0000000c7b17a8a8 RCX: ffff888027668000
> > RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff88805c0bb270
> > RBP: ffffffff8c01fb00 R08: ffffffff82132a15 R09: 1ffff1100b81765f
> > R10: dffffc0000000000 R11: ffffffff846ff540 R12: dffffc0000000000
> > R13: 1ffff1100b817683 R14: dffffc0000000000 R15: dffffc0000000000
> > FS:  0000000000000000(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 00007f43c42de000 CR3: 00000000635f8000 CR4: 0000000000350ef0
> > Call Trace:
> >  <TASK>
> >  security_inode_free+0x4a/0xd0 security/security.c:1613
> >  __destroy_inode+0x2d9/0x650 fs/inode.c:286
> >  destroy_inode fs/inode.c:309 [inline]
> >  evict+0x521/0x630 fs/inode.c:682
> >  dispose_list fs/inode.c:700 [inline]
> >  evict_inodes+0x5f9/0x690 fs/inode.c:750
> >  generic_shutdown_super+0x9d/0x2d0 fs/super.c:626
> >  kill_block_super+0x44/0x90 fs/super.c:1675
> >  deactivate_locked_super+0xc6/0x130 fs/super.c:472
> >  cleanup_mnt+0x426/0x4c0 fs/namespace.c:1267
> >  task_work_run+0x251/0x310 kernel/task_work.c:180
> >  exit_task_work include/linux/task_work.h:38 [inline]
> >  do_exit+0xa1b/0x27e0 kernel/exit.c:878
> >  do_group_exit+0x207/0x2c0 kernel/exit.c:1027
> >  __do_sys_exit_group kernel/exit.c:1038 [inline]
> >  __se_sys_exit_group kernel/exit.c:1036 [inline]
> >  __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1036
> >  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> >  do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
> >  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > RIP: 0033:0x7f731567dd69
> > Code: Unable to access opcode bytes at 0x7f731567dd3f.
> > RSP: 002b:00007fff4f0804d8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> > RAX: ffffffffffffffda RBX: 00007f73156c93a3 RCX: 00007f731567dd69
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> > RBP: 0000000000000002 R08: 00007fff4f07e277 R09: 00007fff4f081790
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff4f081790
> > R13: 00007f73156c937e R14: 00000000000154d0 R15: 000000000000001e
> >  </TASK>
> > Modules linked in:
> > ---[ end trace 0000000000000000 ]---
> 
> -- 
> paul-moore.com
>