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

From: Greg Kroah-Hartman <[email protected]>

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.

The Linux kernel CVE team has assigned CVE-2026-74726 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 5.10.265 with commit f7668762bf5fd6db9397de5c0514407489d9d815
	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 5.15.216 with commit 09add8d5cfa9c46828f51eaad162c36e86366b71
	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 6.1.183 with commit b82f51681a7a88c7d3c865e817a3340d42b5fa2a
	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 6.6.152 with commit dd148539fb4741d01c06b7d2c8bd84b01920756c
	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 6.12.104 with commit dccec0227ed8d9e36936d66e256b957dc2858468
	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 6.18.45 with commit 2faf75a8a06504071b4c0aea7e45a9cc49a4e187
	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 7.1.9 with commit 257c4a3a34d8f51efb00f35375a0c6ce3c8f6ce2
	Issue introduced in 2.6.24 with commit d0e81b7e2246a41d068ecaf15aac9de570816d63 and fixed in 7.2 with commit 683c6ba6e58e6ed1037831ea97dd58d9c0e76b8d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-74726
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/net/bonding/bond_alb.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	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