netdev - [PATCH net] sch_netem: fix skb leak in netem

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Date:   Fri,  2 Mar 2018 21:16:48 +0300
From:   Alexey Kodanev <alexey.kodanev@...cle.com>
To:     netdev@...r.kernel.org
Cc:     Neil Horman <nhorman@...driver.com>,
        David Miller <davem@...emloft.net>,
        Alexey Kodanev <alexey.kodanev@...cle.com>
Subject: [PATCH net] sch_netem: fix skb leak in netem_enqueue()

When we exceed current packets limit and have more than one
segment in the list returned by skb_gso_segment(), netem drops
only the first one, skipping the rest, hence kmemleak reports:

unreferenced object 0xffff880b5d23b600 (size 1024):
  comm "softirq", pid 0, jiffies 4384527763 (age 2770.629s)
  hex dump (first 32 bytes):
    00 80 23 5d 0b 88 ff ff 00 00 00 00 00 00 00 00  ..#]............
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<00000000d8a19b9d>] __alloc_skb+0xc9/0x520
    [<000000001709b32f>] skb_segment+0x8c8/0x3710
    [<00000000c7b9bb88>] tcp_gso_segment+0x331/0x1830
    [<00000000c921cba1>] inet_gso_segment+0x476/0x1370
    [<000000008b762dd4>] skb_mac_gso_segment+0x1f9/0x510
    [<000000002182660a>] __skb_gso_segment+0x1dd/0x620
    [<00000000412651b9>] netem_enqueue+0x1536/0x2590 [sch_netem]
    [<0000000005d3b2a9>] __dev_queue_xmit+0x1167/0x2120
    [<00000000fc5f7327>] ip_finish_output2+0x998/0xf00
    [<00000000d309e9d3>] ip_output+0x1aa/0x2c0
    [<000000007ecbd3a4>] tcp_transmit_skb+0x18db/0x3670
    [<0000000042d2a45f>] tcp_write_xmit+0x4d4/0x58c0
    [<0000000056a44199>] tcp_tasklet_func+0x3d9/0x540
    [<0000000013d06d02>] tasklet_action+0x1ca/0x250
    [<00000000fcde0b8b>] __do_softirq+0x1b4/0x5a3
    [<00000000e7ed027c>] irq_exit+0x1e2/0x210

Fix it by adding the rest of the segments, if any, to skb
'to_free' list in that case.

Fixes: 6071bd1aa13e ("netem: Segment GSO packets on enqueue")
Signed-off-by: Alexey Kodanev <alexey.kodanev@...cle.com>
---
 net/sched/sch_netem.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index 7c179ad..a5023a2 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -508,8 +508,14 @@ static int netem_enqueue(struct sk_buff *skb, struct Qdisc *sch,
 			1<<(prandom_u32() % 8);
 	}
 
-	if (unlikely(sch->q.qlen >= sch->limit))
+	if (unlikely(sch->q.qlen >= sch->limit)) {
+		while (segs) {
+			skb2 = segs->next;
+			__qdisc_drop(segs, to_free);
+			segs = skb2;
+		}
 		return qdisc_drop(skb, sch, to_free);
+	}
 
 	qdisc_qstats_backlog_inc(sch, skb);
 
-- 
1.8.3.1