linux-next test error: KASAN: use-after-free Read in l2cap_sock_release

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: cee5a428 Add linux-next specific files for 20200203
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=167acbf1e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=ea1325a05ecd7b98
dashboard link: https://syzkaller.appspot.com/bug?extid=c3c5bdea7863886115dc
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+c3c5bd...@syzkaller.appspotmail.com

can: request_module (can-proto-0) failed.
can: request_module (can-proto-0) failed.
can: request_module (can-proto-0) failed.
==================================================================
BUG: KASAN: use-after-free in l2cap_sock_release+0x24c/0x290 net/bluetooth/l2cap_sock.c:1212
Read of size 8 at addr ffff8880944904a0 by task syz-fuzzer/9751

CPU: 0 PID: 9751 Comm: syz-fuzzer Not tainted 5.5.0-next-20200203-syzkaller #0
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+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:641
__asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:135
l2cap_sock_release+0x24c/0x290 net/bluetooth/l2cap_sock.c:1212
__sock_release+0xce/0x280 net/socket.c:605
sock_close+0x1e/0x30 net/socket.c:1283
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
do_syscall_64+0x676/0x790 arch/x86/entry/common.c:304
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4afb40
Code: 8b 7c 24 10 48 8b 74 24 18 48 8b 54 24 20 49 c7 c2 00 00 00 00 49 c7 c0 00 00 00 00 49 c7 c1 00 00 00 00 48 8b 44 24 08 0f 05 <48> 3d 01 f0 ff ff 76 20 48 c7 44 24 28 ff ff ff ff 48 c7 44 24 30
RSP: 002b:000000c00020b540 EFLAGS: 00000202 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 000000c00002e500 RCX: 00000000004afb40
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 000000c00020b580 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000000000cc
R13: 00000000000000cb R14: 0000000000000200 R15: 0000000000000200

Allocated by task 9751:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc mm/kasan/common.c:515 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:488
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
__do_kmalloc mm/slab.c:3656 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3665
kmalloc include/linux/slab.h:560 [inline]
sk_prot_alloc+0x23a/0x310 net/core/sock.c:1603
sk_alloc+0x39/0xfd0 net/core/sock.c:1657
l2cap_sock_alloc.constprop.0+0x37/0x230 net/bluetooth/l2cap_sock.c:1603
l2cap_sock_create+0x11e/0x1c0 net/bluetooth/l2cap_sock.c:1649
bt_sock_create+0x16a/0x2d0 net/bluetooth/af_bluetooth.c:130
__sock_create+0x3ce/0x730 net/socket.c:1433
sock_create net/socket.c:1484 [inline]
__sys_socket+0x103/0x220 net/socket.c:1526
__do_sys_socket net/socket.c:1535 [inline]
__se_sys_socket net/socket.c:1533 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1533
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9751:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
kasan_set_free_info mm/kasan/common.c:337 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:476
kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
sk_prot_free net/core/sock.c:1640 [inline]
__sk_destruct+0x5d8/0x7f0 net/core/sock.c:1724
sk_destruct+0xd5/0x110 net/core/sock.c:1739
__sk_free+0xfb/0x3f0 net/core/sock.c:1750
sk_free+0x83/0xb0 net/core/sock.c:1761
sock_put include/net/sock.h:1719 [inline]
l2cap_sock_kill+0x160/0x190 net/bluetooth/l2cap_sock.c:1058
l2cap_sock_release+0x1c3/0x290 net/bluetooth/l2cap_sock.c:1210
__sock_release+0xce/0x280 net/socket.c:605
sock_close+0x1e/0x30 net/socket.c:1283
__fput+0x2ff/0x890 fs/file_table.c:280
____fput+0x16/0x20 fs/file_table.c:313
task_work_run+0x145/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
syscall_return_slowpath arch/x86/entry/common.c:278 [inline]
do_syscall_64+0x676/0x790 arch/x86/entry/common.c:304
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff888094490000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1184 bytes inside of
2048-byte region [ffff888094490000, ffff888094490800)
The buggy address belongs to the page:
page:ffffea0002512400 refcount:1 mapcount:0 mapping:ffff8880aa400e00 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00025123c8 ffffea00021bf608 ffff8880aa400e00
raw: 0000000000000000 ffff888094490000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888094490380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888094490400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888094490480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888094490500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888094490580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[Hillf Danton]

Mon, 03 Feb 2020 11:38:12 -0800 (PST)

Prefetch channel before killing sock.

--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -1193,6 +1193,7 @@ static int l2cap_sock_release(struct soc
{
struct sock *sk = sock->sk;
int err;
+ struct l2cap_chan *chan;

BT_DBG("sock %p, sk %p", sock, sk);

@@ -1202,15 +1203,16 @@ static int l2cap_sock_release(struct soc
bt_sock_unlink(&l2cap_sk_list, sk);

err = l2cap_sock_shutdown(sock, 2);
+ chan = l2cap_pi(sk)->chan;

- l2cap_chan_hold(l2cap_pi(sk)->chan);
- l2cap_chan_lock(l2cap_pi(sk)->chan);
+ l2cap_chan_hold(chan);
+ l2cap_chan_lock(chan);

sock_orphan(sk);
l2cap_sock_kill(sk);

- l2cap_chan_unlock(l2cap_pi(sk)->chan);
- l2cap_chan_put(l2cap_pi(sk)->chan);
+ l2cap_chan_unlock(chan);
+ l2cap_chan_put(chan);

return err;
}

[Marcel Holtmann]

Hi Hillf,

please send a proper patch with commit message and everything. That way I can easily apply it.

Regards

Marcel