CVE-2026-74726bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor

Official description

In the Linux kernel, the following vulnerability has been resolved: bonding: alb: re-check primary_is_promisc under RTNL in bond_alb_monitor bond_alb_monitor() reads primary_is_promisc under RCU, then drops RCU and takes RTNL via rtnl_trylock() before undoing the promiscuity it set on the active slave. In that window the active slave can change under RTNL (RTM_DELLINK -> __bond_release_one() -> bond_alb_handle_active_change()), which already drops the promiscuity and clears primary_is_promisc. The monitor still acts on the stale decision: if the slave was removed with no failover, curr_active_slave is now NULL and the deref faults; if it failed over, the stale dev_set_promiscuity(-1) underflows the new slave's promiscuity counter and pins it in IFF_PROMISC. Oops: general protection fault, probably for non-canonical address ... KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] Workqueue: b42 bond_alb_monitor RIP: 0010:bond_alb_monitor (drivers/net/bonding/bond_alb.c:1600) process_one_work (kernel/workqueue.c:3322) worker_thread (kernel/workqueue.c:3486) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) Kernel panic - not syncing: Fatal exception Re-check primary_is_promisc (and curr_active_slave) after taking RTNL so the monitor only undoes an increment it still owns. The other bonding monitors already re-read state under RTNL in their commit phase (bond_miimon_commit/bond_ab_arp_commit); bond_alb_monitor() was the only one acting on the pre-trylock decision.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/f7668762bf5fd6db9397de5c0514407489d9d815
• https://git.kernel.org/stable/c/09add8d5cfa9c46828f51eaad162c36e86366b71
• https://git.kernel.org/stable/c/b82f51681a7a88c7d3c865e817a3340d42b5fa2a
• https://git.kernel.org/stable/c/dd148539fb4741d01c06b7d2c8bd84b01920756c
• https://git.kernel.org/stable/c/dccec0227ed8d9e36936d66e256b957dc2858468
• https://git.kernel.org/stable/c/2faf75a8a06504071b4c0aea7e45a9cc49a4e187
• https://git.kernel.org/stable/c/257c4a3a34d8f51efb00f35375a0c6ce3c8f6ce2
• https://git.kernel.org/stable/c/683c6ba6e58e6ed1037831ea97dd58d9c0e76b8d