Re: KASAN: use-after-free Read in selinux_netlbl_socket_setsockopt

From: Paul Moore <paul@paul-moore.com>
To: syzbot <syzbot+1bfc00ca3aabe5bcd4cb@syzkaller.appspotmail.com>
Cc: Eric Paris <eparis@parisplace.org>,
	linux-kernel@vger.kernel.org, Stephen Smalley <sds@tycho.nsa.gov>,
	selinux@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: KASAN: use-after-free Read in selinux_netlbl_socket_setsockopt
Date: Wed, 30 Jan 2019 16:30:09 -0500	[thread overview]
Message-ID: <CAHC9VhR9wwqVcnmAVcqfwmRuX02F8oMVzNNNQym-TeceHFLqOQ@mail.gmail.com> (raw)
In-Reply-To: <0000000000003d28d10580b335cd@google.com>

On Wed, Jan 30, 2019 at 4:01 PM syzbot
<syzbot+1bfc00ca3aabe5bcd4cb@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    62967898789d Merge git://git.kernel.org/pub/scm/linux/kern..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=167fdef8c00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4fceea9e2d99ac20
> dashboard link: https://syzkaller.appspot.com/bug?extid=1bfc00ca3aabe5bcd4cb
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+1bfc00ca3aabe5bcd4cb@syzkaller.appspotmail.com
>
> 8021q: adding VLAN 0 to HW filter on device team0
> ==================================================================
> BUG: KASAN: use-after-free in selinux_netlbl_socket_setsockopt+0x49b/0x510
> security/selinux/netlabel.c:525
> Read of size 8 at addr ffff8880a63cf078 by task syz-executor3/18477
>
> CPU: 1 PID: 18477 Comm: syz-executor3 Not tainted 5.0.0-rc4+ #51
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x1db/0x2d0 lib/dump_stack.c:113
>   print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187
>   kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317
>   __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
>   selinux_netlbl_socket_setsockopt+0x49b/0x510
> security/selinux/netlabel.c:525

At first glance this seems odd.  The line above is simply
dereferencing sock->sk_security (getting the "sksec"), which we also
do higher up selinux_socket_setsockopt() via sock_has_perm().  Unless
somehow the socket is being released/freed in the middle of a
setsockopt() syscall this looks like maybe it's something else?

>   selinux_socket_setsockopt+0x67/0x90 security/selinux/hooks.c:4693
>   security_socket_setsockopt+0x7d/0xc0 security/security.c:1467
>   __sys_setsockopt+0xe4/0x3a0 net/socket.c:1892
>   __do_sys_setsockopt net/socket.c:1913 [inline]
>   __se_sys_setsockopt net/socket.c:1910 [inline]
>   __x64_sys_setsockopt+0xbe/0x150 net/socket.c:1910
>   do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x458089
> Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> ff 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fb988b9cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
> RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000458089
> RDX: 0000000000000078 RSI: 0000000000000084 RDI: 000000000000000a
> RBP: 000000000073c040 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb988b9d6d4
> R13: 00000000004cc9e8 R14: 00000000004da6a8 R15: 00000000ffffffff
>
> Allocated by task 18471:
>   save_stack+0x45/0xd0 mm/kasan/common.c:73
>   set_track mm/kasan/common.c:85 [inline]
>   __kasan_kmalloc mm/kasan/common.c:496 [inline]
>   __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:469
>   kasan_kmalloc+0x9/0x10 mm/kasan/common.c:504
>   __do_kmalloc mm/slab.c:3711 [inline]
>   __kmalloc+0x15c/0x740 mm/slab.c:3720
>   kmalloc include/linux/slab.h:550 [inline]
>   sk_prot_alloc+0x19c/0x2e0 net/core/sock.c:1477
>   sk_alloc+0xd7/0x1690 net/core/sock.c:1531
>   nr_create+0xb9/0x5e0 net/netrom/af_netrom.c:436
>   __sock_create+0x532/0x930 net/socket.c:1277
>   sock_create net/socket.c:1317 [inline]
>   __sys_socket+0x106/0x260 net/socket.c:1347
>   __do_sys_socket net/socket.c:1356 [inline]
>   __se_sys_socket net/socket.c:1354 [inline]
>   __x64_sys_socket+0x73/0xb0 net/socket.c:1354
>   do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 18466:
>   save_stack+0x45/0xd0 mm/kasan/common.c:73
>   set_track mm/kasan/common.c:85 [inline]
>   __kasan_slab_free+0x102/0x150 mm/kasan/common.c:458
>   kasan_slab_free+0xe/0x10 mm/kasan/common.c:466
>   __cache_free mm/slab.c:3487 [inline]
>   kfree+0xcf/0x230 mm/slab.c:3806
>   sk_prot_free net/core/sock.c:1514 [inline]
>   __sk_destruct+0x76d/0xa60 net/core/sock.c:1596
>   sk_destruct+0x7b/0x90 net/core/sock.c:1604
>   __sk_free+0xce/0x300 net/core/sock.c:1615
>   sk_free+0x42/0x50 net/core/sock.c:1626
>   sock_put include/net/sock.h:1707 [inline]
>   nr_release+0x337/0x3c0 net/netrom/af_netrom.c:557
>   __sock_release+0xd3/0x250 net/socket.c:579
>   sock_close+0x1b/0x30 net/socket.c:1141
>   __fput+0x3c5/0xb10 fs/file_table.c:278
>   ____fput+0x16/0x20 fs/file_table.c:309
>   task_work_run+0x1f4/0x2b0 kernel/task_work.c:113
>   tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>   exit_to_usermode_loop+0x32a/0x3b0 arch/x86/entry/common.c:166
>   prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>   do_syscall_64+0x696/0x800 arch/x86/entry/common.c:293
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> The buggy address belongs to the object at ffff8880a63cec80
>   which belongs to the cache kmalloc-2k of size 2048
> The buggy address is located 1016 bytes inside of
>   2048-byte region [ffff8880a63cec80, ffff8880a63cf480)
> The buggy address belongs to the page:
> page:ffffea000298f380 count:1 mapcount:0 mapping:ffff88812c3f0c40 index:0x0
> compound_mapcount: 0
> flags: 0x1fffc0000010200(slab|head)
> raw: 01fffc0000010200 ffffea000127f888 ffffea00013a3188 ffff88812c3f0c40
> raw: 0000000000000000 ffff8880a63ce400 0000000100000003 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
>   ffff8880a63cef00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8880a63cef80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8880a63cf000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>                                                                  ^
>   ffff8880a63cf080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>   ffff8880a63cf100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.

-- 
paul moore
www.paul-moore.com