When trying to allocate skb for new PDU, l2cap_chan is unlocked so we can sleep waiting for memory as otherwise there's possible deadlock as fixed in e454c84464. However, in a6a5568c03 lock was moved from socket to channel level and it's no longer safe to just unlock and lock again without checking l2cap_chan state since channel can be disconnected when lock is not held. This patch adds missing checks for l2cap_chan state when returning from call which allocates skb. Scenario is easily reproducible by running rfcomm-tester in a loop. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffffa0442169>] l2cap_do_send+0x29/0x120 [bluetooth] PGD 0 Oops: 0000 [#1] SMP Modules linked in: CPU: 7 PID: 4038 Comm: krfcommd Not tainted 3.14.0-rc2+ #15 Hardware name: Dell Inc. OptiPlex 790/0HY9JP, BIOS A10 11/24/2011 task: ffff8802bdd731c0 ti: ffff8801ec986000 task.ti: ffff8801ec986000 RIP: 0010:[<ffffffffa0442169>] [<ffffffffa0442169>] l2cap_do_send+0x29/0x120 RSP: 0018:ffff8801ec987ad8 EFLAGS: 00010202 RAX: 0000000000000000 RBX: ffff8800c5796800 RCX: 0000000000000000 RDX: ffff880410e7a800 RSI: ffff8802b6c1da00 RDI: ffff8800c5796800 RBP: ffff8801ec987af8 R08: 00000000000000c0 R09: 0000000000000300 R10: 000000000000573b R11: 000000000000573a R12: ffff8802b6c1da00 R13: 0000000000000000 R14: ffff8802b6c1da00 R15: 0000000000000000 FS: 0000000000000000(0000) GS:ffff88042dce0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000041257c000 CR4: 00000000000407e0 Stack: ffff8801ec987d78 ffff8800c5796800 ffff8801ec987d78 0000000000000000 ffff8801ec987ba8 ffffffffa0449e37 0000000000000004 ffff8801ec987af0 ffff8801ec987d40 0000000000000282 0000000000000000 ffffffff00000004 Call Trace: [<ffffffffa0449e37>] l2cap_chan_send+0xaa7/0x1120 [bluetooth] [<ffffffff81770100>] ? _raw_spin_unlock_bh+0x20/0x40 [<ffffffffa045188b>] l2cap_sock_sendmsg+0xcb/0x110 [bluetooth] [<ffffffff81652b0f>] sock_sendmsg+0xaf/0xc0 [<ffffffff810a8381>] ? update_curr+0x141/0x200 [<ffffffff810a8961>] ? dequeue_entity+0x181/0x520 [<ffffffff81652b60>] kernel_sendmsg+0x40/0x60 [<ffffffffa04a8505>] rfcomm_send_frame+0x45/0x70 [rfcomm] [<ffffffff810766f0>] ? internal_add_timer+0x20/0x50 [<ffffffffa04a8564>] rfcomm_send_cmd+0x34/0x60 [rfcomm] [<ffffffffa04a8605>] rfcomm_send_disc+0x75/0xa0 [rfcomm] [<ffffffffa04aacec>] rfcomm_run+0x8cc/0x1a30 [rfcomm] [<ffffffffa04aa420>] ? rfcomm_check_accept+0xc0/0xc0 [rfcomm] [<ffffffff8108e3a9>] kthread+0xc9/0xe0 [<ffffffff8108e2e0>] ? flush_kthread_worker+0xb0/0xb0 [<ffffffff817795fc>] ret_from_fork+0x7c/0xb0 [<ffffffff8108e2e0>] ? flush_kthread_worker+0xb0/0xb0 Code: 00 00 66 66 66 66 90 55 48 89 e5 48 83 ec 20 f6 05 d6 a3 02 00 04 RIP [<ffffffffa0442169>] l2cap_do_send+0x29/0x120 [bluetooth] RSP <ffff8801ec987ad8> CR2: 0000000000000000 Signed-off-by: Andrzej Kaczmarek <andrzej.kaczmarek@xxxxxxxxx> Acked-by: Johan Hedberg <johan.hedberg@xxxxxxxxx> --- v2 added comment regarding why we need to check state again net/bluetooth/l2cap_core.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 6ace116..7bd78c5 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -2434,6 +2434,14 @@ int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len, if (IS_ERR(skb)) return PTR_ERR(skb); + /* Channel lock is released before requesting new skb and then + * reacquired thus we need to recheck channel state. + */ + if (chan->state != BT_CONNECTED) { + kfree_skb(skb); + return -ENOTCONN; + } + l2cap_do_send(chan, skb); return len; } @@ -2483,6 +2491,14 @@ int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len, if (IS_ERR(skb)) return PTR_ERR(skb); + /* Channel lock is released before requesting new skb and then + * reacquired thus we need to recheck channel state. + */ + if (chan->state != BT_CONNECTED) { + kfree_skb(skb); + return -ENOTCONN; + } + l2cap_do_send(chan, skb); err = len; break; -- 1.8.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html