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Concurrent slave enslave/release can mutate the slave list during RCU-protected iteration, changing which slave is "last" mid-loop. This causes the original skb to be double-consumed (double-freed). Replace the racy bond_is_last_slave() check with a simple index comparison (i + 1 == slaves_count) against the pre-snapshot slave count taken via READ_ONCE() before the loop. This preserves the zero-copy optimization for the last slave while making the "last" determination stable against concurrent list mutations. The UAF can trigger the following crash: ================================================================== BUG: KASAN: slab-use-after-free in skb_clone Read of size 8 at addr ffff888100ef8d40 by task exploit/147 CPU: 1 UID: 0 PID: 147 Comm: exploit Not tainted 7.0.0-rc3+ #4 PREEMPTLAZY Call Trace: dump_stack_lvl (lib/dump_stack.c:123) print_report (mm/kasan/report.c:379 mm/kasan/report.c:482) kasan_report (mm/kasan/report.c:597) skb_clone (include/linux/skbuff.h:1724 include/linux/skbuff.h:1792 include/linux/skbuff.h:3396 net/core/skbuff.c:2108) bond_xmit_broadcast (drivers/net/bonding/bond_main.c:5334) bond_start_xmit (drivers/net/bonding/bond_main.c:5567 drivers/net/bonding/bond_main.c:5593) dev_hard_start_xmit (include/linux/netdevice.h:5325 include/linux/netdevice.h:5334 net/core/dev.c:3871 net/core/dev.c:3887) __dev_queue_xmit (include/linux/netdevice.h:3601 net/core/dev.c:4838) ip6_finish_output2 (include/net/neighbour.h:540 include/net/neighbour.h:554 net/ipv6/ip6_output.c:136) ip6_finish_output (net/ipv6/ip6_output.c:208 net/ipv6/ip6_output.c:219) ip6_output (net/ipv6/ip6_output.c:250) ip6_send_skb (net/ipv6/ip6_output.c:1985) udp_v6_send_skb (net/ipv6/udp.c:1442) udpv6_sendmsg (net/ipv6/udp.c:1733) __sys_sendto (net/socket.c:730 net/socket.c:742 net/socket.c:2206) __x64_sys_sendto (net/socket.c:2209) do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) Allocated by task 147: Freed by task 147: The buggy address belongs to the object at ffff888100ef8c80 which belongs to the cache skbuff_head_cache of size 224 The buggy address is located 192 bytes inside of freed 224-byte region [ffff888100ef8c80, ffff888100ef8d60) Memory state around the buggy address: ffff888100ef8c00: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc ffff888100ef8c80: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff888100ef8d00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc ^ ffff888100ef8d80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb ffff888100ef8e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== Fixes: 4e5bd03ae346 ("net: bonding: fix bond_xmit_broadcast return value error bug") Reported-by: Weiming Shi Change-Id: I2349f4953b5760b7f4a12da583aa779c19c4b59c Signed-off-by: Xiang Mei Link: https://patch.msgid.link/20260326075553.3960562-1-xmei5@asu.edu Signed-off-by: Paolo Abeni [Kevin Berry : fixed merge conflicts and adapted to 6.12 struct] Signed-off-by: Chenglong Tang --- drivers/net/bonding/bond_main.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index 2ac455a9d1bb..fb8d7fec27ee 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -5346,23 +5346,33 @@ static netdev_tx_t bond_3ad_xor_xmit(struct sk_buff *skb, return bond_tx_drop(dev, skb); } -/* in broadcast mode, we send everything to all usable interfaces. */ +/* in broadcast mode, we send everything to all or usable slave interfaces. + * under rcu_read_lock when this function is called. + */ static netdev_tx_t bond_xmit_broadcast(struct sk_buff *skb, - struct net_device *bond_dev) + struct net_device *bond_dev, + bool all_slaves) { struct bonding *bond = netdev_priv(bond_dev); - struct slave *slave = NULL; - struct list_head *iter; + struct bond_up_slave *slaves; bool xmit_suc = false; bool skb_used = false; + int slaves_count, i; - bond_for_each_slave_rcu(bond, slave, iter) { + if (all_slaves) + slaves = rcu_dereference(bond->all_slaves); + else + slaves = rcu_dereference(bond->usable_slaves); + + slaves_count = slaves ? READ_ONCE(slaves->count) : 0; + for (i = 0; i < slaves_count; i++) { + struct slave *slave = slaves->arr[i]; struct sk_buff *skb2; if (!(bond_slave_is_up(slave) && slave->link == BOND_LINK_UP)) continue; - if (bond_is_last_slave(bond, slave)) { + if (i + 1 == slaves_count) { skb2 = skb; skb_used = true; } else { @@ -5597,7 +5607,7 @@ static netdev_tx_t __bond_start_xmit(struct sk_buff *skb, struct net_device *dev case BOND_MODE_XOR: return bond_3ad_xor_xmit(skb, dev); case BOND_MODE_BROADCAST: - return bond_xmit_broadcast(skb, dev); + return bond_xmit_broadcast(skb, dev, true); case BOND_MODE_ALB: return bond_alb_xmit(skb, dev); case BOND_MODE_TLB: -- 2.54.0.rc0.605.g598a273b03-goog