Bluetooth: don't attempt to free a channel that wasn't created

We may currently attempt to free a channel which wasn't created due to
an error in the initialization path, this would cause a NULL ptr deref.

This would cause the following oops:

[   12.919073] BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
[   12.919131] IP: [<ffffffff836645c4>] l2cap_chan_put+0x34/0x50
[   12.919135] PGD 0
[   12.919138] Oops: 0002 [#1] PREEMPT SMP DEBUG_PAGEALLOC
[   12.919193] Dumping ftrace buffer:
[   12.919242]    (ftrace buffer empty)
[   12.919314] Modules linked in:
[   12.919318] CPU 1
[   12.919319] Pid: 6210, comm: krfcommd Tainted: G        W    3.6.0-next-20121004-sasha-00005-gb010653-dirty #30
[   12.919374] RIP: 0010:[<ffffffff836645c4>]  [<ffffffff836645c4>] l2cap_chan_put+0x34/0x50
[   12.919377] RSP: 0000:ffff880066933c38  EFLAGS: 00010246
[   12.919378] RAX: ffffffff8366c780 RBX: 0000000000000000 RCX: 6666666666666667
[   12.919379] RDX: 0000000000000fa0 RSI: ffffffff84d3f79e RDI: 0000000000000010
[   12.919381] RBP: ffff880066933c48 R08: ffffffff859989f8 R09: 0000000000000001
[   12.919382] R10: 0000000000000000 R11: 7fffffffffffffff R12: 0000000000000000
[   12.919383] R13: ffff88009b00a200 R14: ffff88009b00a200 R15: 0000000000000001
[   12.919385] FS:  0000000000000000(0000) GS:ffff880033600000(0000) knlGS:0000000000000000
[   12.919437] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   12.919440] CR2: 0000000000000010 CR3: 0000000005026000 CR4: 00000000000406e0
[   12.919446] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   12.919451] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[   12.919504] Process krfcommd (pid: 6210, threadinfo ffff880066932000, task ffff880065c4b000)
[   12.919506] Stack:
[   12.919510]  ffff88009b00a200 ffff880032084000 ffff880066933c68 ffffffff8366c7bc
[   12.919513]  7fffffffffffffff ffff880032084000 ffff880066933c98 ffffffff833ae0ae
[   12.919516]  ffff880066933ca8 0000000000000000 0000000000000000 ffff88009b00a200
[   12.919517] Call Trace:
[   12.919522]  [<ffffffff8366c7bc>] l2cap_sock_destruct+0x3c/0x80
[   12.919527]  [<ffffffff833ae0ae>] __sk_free+0x1e/0x1f0
[   12.919530]  [<ffffffff833ae2f7>] sk_free+0x17/0x20
[   12.919585]  [<ffffffff8366ca4e>] l2cap_sock_alloc.constprop.5+0x9e/0xd0
[   12.919591]  [<ffffffff8366cb9e>] l2cap_sock_create+0x7e/0x100
[   12.919652]  [<ffffffff83a4f32a>] ? _raw_read_lock+0x6a/0x80
[   12.919658]  [<ffffffff836402c4>] ? bt_sock_create+0x74/0x110
[   12.919660]  [<ffffffff83640308>] bt_sock_create+0xb8/0x110
[   12.919664]  [<ffffffff833aa232>] __sock_create+0x282/0x3b0
[   12.919720]  [<ffffffff833aa0b0>] ? __sock_create+0x100/0x3b0
[   12.919725]  [<ffffffff836785b0>] ? rfcomm_process_sessions+0x17e0/0x17e0
[   12.919779]  [<ffffffff833aa37f>] sock_create_kern+0x1f/0x30
[   12.919784]  [<ffffffff83675714>] rfcomm_l2sock_create+0x44/0x70
[   12.919787]  [<ffffffff836785b0>] ? rfcomm_process_sessions+0x17e0/0x17e0
[   12.919790]  [<ffffffff836785fe>] rfcomm_run+0x4e/0x1f0
[   12.919846]  [<ffffffff836785b0>] ? rfcomm_process_sessions+0x17e0/0x17e0
[   12.919852]  [<ffffffff81138ee3>] kthread+0xe3/0xf0
[   12.919908]  [<ffffffff8117b12e>] ? put_lock_stats.isra.14+0xe/0x40
[   12.919914]  [<ffffffff81138e00>] ? flush_kthread_work+0x1f0/0x1f0
[   12.919968]  [<ffffffff83a5077c>] ret_from_fork+0x7c/0x90
[   12.919973]  [<ffffffff81138e00>] ? flush_kthread_work+0x1f0/0x1f0
[   12.920161] Code: 83 ec 08 f6 05 ff 58 44 02 04 74 1b 8b 4f 10 48 89 fa 48 c7 c6 d9 d7 d4 84 48 c7 c7 80 9e aa 85 31 c0 e8 80
ac 3a fe 48 8d 7b 10 <f0> 83 6b 10 01 0f 94 c0 84 c0 74 05 e8 8b e0 ff ff 48 83 c4 08
[   12.920165] RIP  [<ffffffff836645c4>] l2cap_chan_put+0x34/0x50
[   12.920166]  RSP <ffff880066933c38>
[   12.920167] CR2: 0000000000000010
[   12.920417] ---[ end trace 5a9114e8a158ab84 ]---

Introduced in commit 61d6ef3e ("Bluetooth: Make better use of l2cap_chan
reference counting").
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

net/bluetooth/l2cap_sock.c

@@ -1083,6 +1083,7 @@ static void l2cap_sock_destruct(struct sock *sk)
 {
 	BT_DBG("sk %p", sk);
 
+	if (l2cap_pi(sk)->chan)
 		l2cap_chan_put(l2cap_pi(sk)->chan);
 	if (l2cap_pi(sk)->rx_busy_skb) {
 		kfree_skb(l2cap_pi(sk)->rx_busy_skb);