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authorPaolo Abeni <pabeni@redhat.com>2019-09-12 12:02:42 +0200
committerDavid S. Miller <davem@davemloft.net>2019-09-15 20:35:55 +0200
commitd518d2ed8640c1cbbbb6f63939e3e65471817367 (patch)
tree7b953ec465e856df26ee7cb93983f3bec1495d42 /net
parent1609d7604b847a9820e63393d1a3b6cac7286d40 (diff)
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net/sched: fix race between deactivation and dequeue for NOLOCK qdisc
The test implemented by some_qdisc_is_busy() is somewhat loosy for NOLOCK qdisc, as we may hit the following scenario: CPU1 CPU2 // in net_tx_action() clear_bit(__QDISC_STATE_SCHED...); // in some_qdisc_is_busy() val = (qdisc_is_running(q) || test_bit(__QDISC_STATE_SCHED, &q->state)); // here val is 0 but... qdisc_run(q) // ... CPU1 is going to run the qdisc next As a conseguence qdisc_run() in net_tx_action() can race with qdisc_reset() in dev_qdisc_reset(). Such race is not possible for !NOLOCK qdisc as both the above bit operations are under the root qdisc lock(). After commit 021a17ed796b ("pfifo_fast: drop unneeded additional lock on dequeue") the race can cause use after free and/or null ptr dereference, but the root cause is likely older. This patch addresses the issue explicitly checking for deactivation under the seqlock for NOLOCK qdisc, so that the qdisc_run() in the critical scenario becomes a no-op. Note that the enqueue() op can still execute concurrently with dev_qdisc_reset(), but that is safe due to the skb_array() locking, and we can't avoid that for NOLOCK qdiscs. Fixes: 021a17ed796b ("pfifo_fast: drop unneeded additional lock on dequeue") Reported-by: Li Shuang <shuali@redhat.com> Reported-and-tested-by: Davide Caratti <dcaratti@redhat.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/dev.c16
1 files changed, 10 insertions, 6 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index 5156c0edebe8..4ed9df74eb8a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3467,18 +3467,22 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
qdisc_calculate_pkt_len(skb, q);
if (q->flags & TCQ_F_NOLOCK) {
- if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) {
- __qdisc_drop(skb, &to_free);
- rc = NET_XMIT_DROP;
- } else if ((q->flags & TCQ_F_CAN_BYPASS) && q->empty &&
- qdisc_run_begin(q)) {
+ if ((q->flags & TCQ_F_CAN_BYPASS) && q->empty &&
+ qdisc_run_begin(q)) {
+ if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED,
+ &q->state))) {
+ __qdisc_drop(skb, &to_free);
+ rc = NET_XMIT_DROP;
+ goto end_run;
+ }
qdisc_bstats_cpu_update(q, skb);
+ rc = NET_XMIT_SUCCESS;
if (sch_direct_xmit(skb, q, dev, txq, NULL, true))
__qdisc_run(q);
+end_run:
qdisc_run_end(q);
- rc = NET_XMIT_SUCCESS;
} else {
rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
qdisc_run(q);