net/sched: sch_teql: fix use-after-free on lower qdisc drop

The issue: teql_master_xmit() tests the slave's ndo_start_xmit() return
value against NETDEV_TX_OK alone. A slave that consumes the skb but
returns an error code (rc < NET_XMIT_MASK, e.g. NET_XMIT_DROP) is treated
as if the skb were still owned, so the loop restores skb->dev and calls
__skb_pull() on it. A VLAN slave returns the result of dev_queue_xmit()
from its ndo_start_xmit() (propagated since cbbef5e18307), and when the
lower qdisc drops the packet that value is NET_XMIT_DROP after the skb
has been freed, giving a use-after-free in teql_master_xmit().

The Fix: test for consumption with dev_xmit_complete(), which accepts
NETDEV_TX_OK and every rc < NET_XMIT_MASK, matching other callers that
need to distinguish consumed results from busy. Only NETDEV_TX_OK keeps
the packet counted in tx_packets/tx_bytes and advances the slave; a
consumed result that is neither a success nor NET_XMIT_CN ends the
attempt and is charged to tx_dropped, so lower-qdisc drops are no longer
reported as good transmits. NET_XMIT_CN is counted like success because
it can accompany acceptance of the current packet: pfifo_head_drop drops
the old head, enqueues the current skb and returns NET_XMIT_CN.

Conditions to recreate the bug:
With CONFIG_NET_SCH_TEQL,
CONFIG_VLAN_8021Q and CONFIG_DUMMY enabled, add lkrdummy0 (dummy) and
lkrvlan0 (VLAN id 37 on lkrdummy0); set a pfifo limit 0 root on lkrdummy0
and a teql0 root on lkrvlan0; bring teql0 up with an address and send one
UDP packet to it. The VLAN xmit returns NET_XMIT_DROP from the lower
qdisc while holding a freed skb.

Fixes: 572a9d7b6fc7 ("net: allow to propagate errors through ->ndo_hard_start_xmit()")
Link: https://lore.kernel.org/netdev/179248763469.3135.1739559328868319628@kernel.org/
Link: https://lore.kernel.org/netdev/20261023162821.GN708417@horms.kernel.org/
Cc: stable@vger.kernel.org
Signed-off-by: owen kwan <owen@verialabs.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/QDISC-Y0BY.v2.r0.20261024060625-2@mojatatu.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

0 files changed, 0 insertions, 0 deletions