7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: owen kwan commit 782d6bb8f9b8e9d8591181662222bf74cd3ecf79 upstream. 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 Signed-off-by: Jamal Hadi Salim Reviewed-by: Simon Horman Link: https://patch.msgid.link/QDISC-Y0BY.v2.r0.20261024060625-2@mojatatu.com Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman --- net/sched/sch_teql.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) --- a/net/sched/sch_teql.c +++ b/net/sched/sch_teql.c @@ -347,12 +347,18 @@ restart: case 0: if (__netif_tx_trylock(slave_txq)) { unsigned int length = qdisc_pkt_len(skb); + int rc = NETDEV_TX_BUSY; skb->dev = slave; - if (!netif_xmit_frozen_or_stopped(slave_txq) && - netdev_start_xmit(skb, slave, slave_txq, false) == - NETDEV_TX_OK) { - __netif_tx_unlock(slave_txq); + if (!netif_xmit_frozen_or_stopped(slave_txq)) + rc = netdev_start_xmit(skb, slave, slave_txq, false); + __netif_tx_unlock(slave_txq); + if (dev_xmit_complete(rc)) { + if (rc != NETDEV_TX_OK && rc != NET_XMIT_CN) { + master->tx_dropped++; + rcu_read_unlock(); + return NETDEV_TX_OK; + } raw_spin_lock_irqsave(&master->slaves_lock, flags); if (rcu_dereference_protected(master->slaves, lockdep_is_held(&master->slaves_lock)) == q) @@ -366,7 +372,6 @@ restart: rcu_read_unlock(); return NETDEV_TX_OK; } - __netif_tx_unlock(slave_txq); } if (netif_xmit_stopped(netdev_get_tx_queue(dev, 0))) busy = 1;