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Paolo Abeni d518d2ed86 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 021a17ed79 ("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: 021a17ed79 ("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>
2019-09-15 20:35:55 +02:00
..
acpi
asm-generic include/asm-generic/5level-fixup.h: fix variable 'p4d' set but not used 2019-08-13 16:06:52 -07:00
clocksource
crypto
drm drm/fb-helper: Instanciate shadow FB if configured in device's mode_config 2019-08-01 15:01:35 +02:00
dt-bindings ARM: Device-tree updates 2019-07-19 17:19:24 -07:00
keys
kvm KVM: arm/arm64: Sync ICH_VMCR_EL2 back when about to block 2019-08-05 15:36:46 +01:00
linux Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-14 12:20:38 -07:00
math-emu nds32: Mark expected switch fall-throughs 2019-08-29 11:06:56 -05:00
media
misc auxdisplay: charlcd: move charlcd.h to drivers/auxdisplay 2019-08-08 19:59:17 +02:00
net net/sched: fix race between deactivation and dequeue for NOLOCK qdisc 2019-09-15 20:35:55 +02:00
pcmcia
ras
rdma RDMA/restrack: Rewrite PID namespace check to be reliable 2019-08-20 13:44:44 -04:00
scsi scsi: fcoe: Embed fc_rport_priv in fcoe_rport structure 2019-07-29 21:12:35 -04:00
soc ARC updates for 5.3-rc7 2019-08-27 10:50:27 -07:00
sound sound fixes for 5.3-rc4 2019-08-09 09:21:27 -07:00
target
trace rxrpc: Use skb_unshare() rather than skb_cow_data() 2019-08-27 10:13:46 +01:00
uapi Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2019-09-14 12:20:38 -07:00
vdso
video drm main pull request for v5.3-rc1 (sans mm changes) 2019-07-15 19:04:27 -07:00
xen xen: avoid link error on ARM 2019-07-31 08:14:12 +02:00
Kbuild kbuild: add net/netfilter/nf_tables_offload.h to header-test blacklist. 2019-07-21 11:43:43 -07:00