KASAN: use-after-free Read in selinux_netlbl_socket_setsockopt

[syzbot]

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+1bfc00...@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
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
==================================================================


---
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[Paul Moore]

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?

--
paul moore
www.paul-moore.com

[Dmitry Vyukov]

Hi Paul,

Searching for af_netrom across other syzbot bugs:
https://groups.google.com/forum/#!searchin/syzkaller-bugs/af_netrom%7Csort:date

I see at least:
https://syzkaller.appspot.com/bug?extid=b0b1952f5864b4009b09
https://syzkaller.appspot.com/bug?extid=febf3c50d4262e578b1c
https://syzkaller.appspot.com/bug?extid=defa700d16f1bd1b9a05

Which suggests there are some serious lifetime problems in netrom
sockets. That would probably explain this crash as well.

+netrom maintainers, does this explanation look plausible to you?
should we dup this crash onto one of the other netrom bugs? and
perhaps these netrom bugs across themselves too?

[Paul Moore]

That definitely looks plausible. While I'm not one to say it could
*never* be the SELinux/NetLabel code, I can say that the SELinux code
path in question hasn't changed in some time so I would be a little
surprised if it was suddenly broken.

> +netrom maintainers, does this explanation look plausible to you?
> should we dup this crash onto one of the other netrom bugs? and
> perhaps these netrom bugs across themselves too?

--
paul moore
www.paul-moore.com

[Cong Wang]

On Thu, Jan 31, 2019 at 10:56 PM Dmitry Vyukov <dvy...@google.com> wrote:
> Hi Paul,
>
> Searching for af_netrom across other syzbot bugs:
> https://groups.google.com/forum/#!searchin/syzkaller-bugs/af_netrom%7Csort:date
>
> I see at least:
> https://syzkaller.appspot.com/bug?extid=b0b1952f5864b4009b09
> https://syzkaller.appspot.com/bug?extid=febf3c50d4262e578b1c
> https://syzkaller.appspot.com/bug?extid=defa700d16f1bd1b9a05
>
> Which suggests there are some serious lifetime problems in netrom
> sockets. That would probably explain this crash as well.

This is supposed to be fixed by:
https://git.kernel.org/pub/scm/linux/kernel/git/davem/net.git/commit/?id=63346650c1a94a92be61a57416ac88c0a47c4327

Please let me know if it isn't.

Thanks.

[Dmitry Vyukov]

syzbot can tell if it's not fixed, but for that we need to mark these
bugs as fixed, otherwise syzbot will just consider any new crashes as
the same old bug so nothing to notify about.

#syz fix: netrom: switch to sock timer API