From: Paolo Abeni pabeni@redhat.com
[ Upstream commit d518d2ed8640c1cbbbb6f63939e3e65471817367 ]
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/net/pkt_sched.h | 7 ++++++- net/core/dev.c | 16 ++++++++++------ 2 files changed, 16 insertions(+), 7 deletions(-)
--- a/include/net/pkt_sched.h +++ b/include/net/pkt_sched.h @@ -118,7 +118,12 @@ void __qdisc_run(struct Qdisc *q); static inline void qdisc_run(struct Qdisc *q) { if (qdisc_run_begin(q)) { - __qdisc_run(q); + /* NOLOCK qdisc must check 'state' under the qdisc seqlock + * to avoid racing with dev_qdisc_reset() + */ + if (!(q->flags & TCQ_F_NOLOCK) || + likely(!test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) + __qdisc_run(q); qdisc_run_end(q); } } --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3467,18 +3467,22 @@ static inline int __dev_xmit_skb(struct 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);