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SubjectRe: [PATCH] bluetooth/rfcomm: fix ODEBUG bug in rfcomm_dev_ioctl
Hello,

syzbot found the following crash on:

HEAD commit: fb279f4e Merge branch 'i2c/for-current-fixed' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=168c481de00000
kernel config: https://syzkaller.appspot.com/x/.config?x=8b13b05f0e61d957
dashboard link: https://syzkaller.appspot.com/bug?extid=4496e82090657320efc6
compiler: clang version 10.0.0
(https://github.com/llvm/llvm-project/
c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

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+4496e82090657320efc6@syzkaller.appspotmail.com

------------[ cut here ]------------
ODEBUG: free active (active state 0) object type: timer_list hint:
rfcomm_dlc_timeout+0x0/0xc0 net/bluetooth/rfcomm/core.c:300
WARNING: CPU: 0 PID: 9181 at lib/debugobjects.c:488 debug_print_object
lib/debugobjects.c:485 [inline]
WARNING: CPU: 0 PID: 9181 at lib/debugobjects.c:488
__debug_check_no_obj_freed lib/debugobjects.c:967 [inline]
WARNING: CPU: 0 PID: 9181 at lib/debugobjects.c:488
debug_check_no_obj_freed+0x45c/0x640 lib/debugobjects.c:998
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 9181 Comm: syz-executor.3 Not tainted 5.6.0-rc3-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+0x1e9/0x30e lib/dump_stack.c:118
panic+0x264/0x7a0 kernel/panic.c:221
__warn+0x209/0x210 kernel/panic.c:582
report_bug+0x1ac/0x2d0 lib/bug.c:195
fixup_bug arch/x86/kernel/traps.c:174 [inline]
do_error_trap+0xca/0x1c0 arch/x86/kernel/traps.c:267
do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:debug_print_object lib/debugobjects.c:485 [inline]
RIP: 0010:__debug_check_no_obj_freed lib/debugobjects.c:967 [inline]
RIP: 0010:debug_check_no_obj_freed+0x45c/0x640 lib/debugobjects.c:998
Code: 74 08 4c 89 f7 e8 64 2d 18 fe 4d 8b 06 48 c7 c7 53 10 d1 88 48
c7 c6 0f 01 cf 88 48 89 da 89 e9 4d 89 f9 31 c0 e8 c4 cd ae fd <0f> 0b
48 ba 00 00 00 00 00 fc ff df ff 05 c6 39 b1 05 48 8b 5c 24
RSP: 0018:ffffc90001907c88 EFLAGS: 00010046
RAX: 72f8f847df918a00 RBX: ffffffff88d4edca RCX: 0000000000040000
RDX: ffffc90011373000 RSI: 0000000000013ee9 RDI: 0000000000013eea
RBP: 0000000000000000 R08: ffffffff815e1276 R09: ffffed1015d04592
R10: ffffed1015d04592 R11: 0000000000000000 R12: ffff88808ea6fbac
R13: ffffffff8b592e40 R14: ffffffff890ddc78 R15: ffffffff873dcc50
kfree+0xfc/0x220 mm/slab.c:3756
rfcomm_dlc_put include/net/bluetooth/rfcomm.h:258 [inline]
__rfcomm_create_dev net/bluetooth/rfcomm/tty.c:417 [inline]
rfcomm_create_dev net/bluetooth/rfcomm/tty.c:486 [inline]
rfcomm_dev_ioctl+0xe37/0x2340 net/bluetooth/rfcomm/tty.c:588
rfcomm_sock_ioctl+0x79/0xa0 net/bluetooth/rfcomm/sock.c:902
sock_do_ioctl+0x7b/0x260 net/socket.c:1053
sock_ioctl+0x4aa/0x690 net/socket.c:1204
vfs_ioctl fs/ioctl.c:47 [inline]
ksys_ioctl fs/ioctl.c:763 [inline]
__do_sys_ioctl fs/ioctl.c:772 [inline]
__se_sys_ioctl+0xf9/0x160 fs/ioctl.c:770
do_syscall_64+0xf3/0x1b0 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c4a9
Code: ad b6 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fd490578c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd4905796d4 RCX: 000000000045c4a9
RDX: 0000000020000100 RSI: 00000000400452c8 RDI: 0000000000000004
RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000317 R14: 00000000004c5443 R15: 000000000076bf2c
Kernel Offset: disabled
Rebooting in 86400 seconds..

Qiujun Huang <hqjagain@gmail.com> 于2020年3月7日周六 下午10:00写道:
>
> Needn't call 'rfcomm_dlc_put' here, because 'rfcomm_dlc_exists' didn't
> increase dlc->refcnt.
>
> Reported-by: syzbot+4496e82090657320efc6@syzkaller.appspotmail.com
> Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
> ---
> net/bluetooth/rfcomm/tty.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
> index 0c7d31c..ea2a1df0 100644
> --- a/net/bluetooth/rfcomm/tty.c
> +++ b/net/bluetooth/rfcomm/tty.c
> @@ -414,7 +414,6 @@ static int __rfcomm_create_dev(struct sock *sk, void __user *arg)
> if (IS_ERR(dlc))
> return PTR_ERR(dlc);
> else if (dlc) {
> - rfcomm_dlc_put(dlc);
> return -EBUSY;
> }
> dlc = rfcomm_dlc_alloc(GFP_KERNEL);
> --
> 1.8.3.1
>

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