linux-kernel - [PATCH RT v3] net/xfrm/input: Protect queue with lock

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Date:   Tue, 26 Nov 2019 08:13:35 +0100
From:   Joerg Vehlow <lkml@...coder.de>
To:     linux-kernel@...r.kernel.org, bigeasy@...utronix.de,
        trix@...hat.com
Cc:     Joerg Vehlow <joerg.vehlow@...-tech.de>
Subject: [PATCH RT v3] net/xfrm/input: Protect queue with lock

From: Joerg Vehlow <joerg.vehlow@...-tech.de>

During the skb_queue_splice_init the tasklet could have been preempted
and_skb_queue_tail called, which led to an inconsistent queue.

Affected are all rt kernels up to 5.0.19-rt11 (due to bh rework).

It was found using ipsec stress tests (e.g. ipcomp) in ltp suite.
Running them in a continous loop triggered the bug in qemu within 5-10 retries.

[  139.717259] BUG: unable to handle kernel NULL pointer dereference at 0000000000000518
[  139.717260] PGD 0 P4D 0
[  139.717262] Oops: 0000 [#1] PREEMPT SMP PTI
[  139.717273] CPU: 2 PID: 11987 Comm: netstress Not tainted 4.19.59-rt24-preemt-rt #1
[  139.717274] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014
[  139.717306] RIP: 0010:xfrm_trans_reinject+0x97/0xd0
[  139.717307] Code: 42 eb 45 83 6d b0 01 31 f6 48 8b 42 08 48 c7 42 08 00 00 00 00 48 8b 0a 48 c7 02 00 00 00 00 48 89 41 08 48 89 08 48 8b 42 10 <48> 8b b8 18 05 00 00 48 8b 42 40 e8 d9 e1 4b 00 48 8b 55 a0 48 39
[  139.717307] RSP: 0018:ffffc900007b37e8 EFLAGS: 00010246
[  139.717308] RAX: 0000000000000000 RBX: ffffc900007b37e8 RCX: ffff88807db206a8
[  139.717309] RDX: ffff88807db206a8 RSI: 0000000000000000 RDI: 0000000000000000
[  139.717309] RBP: ffffc900007b3848 R08: 0000000000000001 R09: ffffc900007b35c8
[  139.717309] R10: ffffea0001dcfc00 R11: 00000000000890c4 R12: ffff88807db20680
[  139.717310] R13: 00000000000f4240 R14: 0000000000000000 R15: 0000000000000000
[  139.717310] FS:  00007f4643034700(0000) GS:ffff88807db00000(0000) knlGS:0000000000000000
[  139.717311] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  139.717337] CR2: 0000000000000518 CR3: 00000000769c6000 CR4: 00000000000006e0
[  139.717350] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  139.717350] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  139.717350] Call Trace:
[  139.717387]  tasklet_action_common.isra.18+0x6d/0xd0
[  139.717388]  tasklet_action+0x1d/0x20
[  139.717389]  do_current_softirqs+0x196/0x360
[  139.717390]  __local_bh_enable+0x51/0x60
[  139.717397]  ip_finish_output2+0x18b/0x3f0
[  139.717408]  ? task_rq_lock+0x53/0xe0
[  139.717415]  ip_finish_output+0xbe/0x1b0
[  139.717416]  ip_output+0x72/0x100
[  139.717422]  ? ipcomp_output+0x5e/0x280
[  139.717424]  xfrm_output_resume+0x4b5/0x540
[  139.717436]  ? refcount_dec_and_test_checked+0x11/0x20
[  139.717443]  ? kfree_skbmem+0x33/0x80
[  139.717444]  xfrm_output+0xd7/0x110
[  139.717451]  xfrm4_output_finish+0x2b/0x30
[  139.717452]  __xfrm4_output+0x3a/0x50
[  139.717453]  xfrm4_output+0x40/0xe0
[  139.717454]  ? xfrm_dst_check+0x174/0x250
[  139.717455]  ? xfrm4_output+0x40/0xe0
[  139.717456]  ? xfrm_dst_check+0x174/0x250
[  139.717457]  ip_local_out+0x3b/0x50
[  139.717458]  __ip_queue_xmit+0x16b/0x420
[  139.717464]  ip_queue_xmit+0x10/0x20
[  139.717466]  __tcp_transmit_skb+0x566/0xad0
[  139.717467]  tcp_write_xmit+0x3a4/0x1050
[  139.717468]  __tcp_push_pending_frames+0x35/0xe0
[  139.717469]  tcp_push+0xdb/0x100
[  139.717469]  tcp_sendmsg_locked+0x491/0xd70
[  139.717470]  tcp_sendmsg+0x2c/0x50
[  139.717476]  inet_sendmsg+0x3e/0xf0
[  139.717483]  sock_sendmsg+0x3e/0x50
[  139.717484]  __sys_sendto+0x114/0x1a0
[  139.717491]  ? __rt_mutex_unlock+0xe/0x10
[  139.717492]  ? _mutex_unlock+0xe/0x10
[  139.717500]  ? ksys_write+0xc5/0xe0
[  139.717501]  __x64_sys_sendto+0x28/0x30
[  139.717503]  do_syscall_64+0x4d/0x110
[  139.717504]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Joerg Vehlow <joerg.vehlow@...-tech.de>
---
 net/xfrm/xfrm_input.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_input.c b/net/xfrm/xfrm_input.c
index 790b514f86b6..4c4e669fcd16 100644
--- a/net/xfrm/xfrm_input.c
+++ b/net/xfrm/xfrm_input.c
@@ -512,12 +512,15 @@ EXPORT_SYMBOL(xfrm_input_resume);
 
 static void xfrm_trans_reinject(unsigned long data)
 {
+	unsigned long flags;
 	struct xfrm_trans_tasklet *trans = (void *)data;
 	struct sk_buff_head queue;
 	struct sk_buff *skb;
 
 	__skb_queue_head_init(&queue);
+	spin_lock_irqsave(&trans->queue.lock, flags);
 	skb_queue_splice_init(&trans->queue, &queue);
+	spin_unlock_irqrestore(&trans->queue.lock, flags);
 
 	while ((skb = __skb_dequeue(&queue)))
 		XFRM_TRANS_SKB_CB(skb)->finish(dev_net(skb->dev), NULL, skb);
@@ -535,7 +538,7 @@ int xfrm_trans_queue(struct sk_buff *skb,
 		return -ENOBUFS;
 
 	XFRM_TRANS_SKB_CB(skb)->finish = finish;
-	__skb_queue_tail(&trans->queue, skb);
+	skb_queue_tail(&trans->queue, skb);
 	tasklet_schedule(&trans->tasklet);
 	return 0;
 }
@@ -560,7 +563,7 @@ void __init xfrm_input_init(void)
 		struct xfrm_trans_tasklet *trans;
 
 		trans = &per_cpu(xfrm_trans_tasklet, i);
-		__skb_queue_head_init(&trans->queue);
+		skb_queue_head_init(&trans->queue);
 		tasklet_init(&trans->tasklet, xfrm_trans_reinject,
 			     (unsigned long)trans);
 	}
-- 
2.20.1