CVE-2026-72321ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer()

Official description

In the Linux kernel, the following vulnerability has been resolved: ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer() When a timer is deleted and not re-armed in igmp_mod_timer(), or stopped in igmp_stop_timer(), the code currently decrements the reference counter of the multicast list entry @im using refcount_dec(&im->refcnt). However, both functions can be called from the RCU reader path: - igmp_mod_timer() via igmp_heard_query() -> for_each_pmc_rcu() - igmp_stop_timer() via igmp_rcv() -> igmp_heard_report() If the group im was concurrently removed from the list by ip_mc_dec_group(), its reference count might have already been decremented to 1. In this case, timer_delete() succeeds, and refcount_dec() decrements the refcount from 1 to 0. Since refcount_dec() does not free the object when it hits 0 (unlike ip_ma_put()), the im structure is leaked. Fix this by using ip_ma_put(im) instead of refcount_dec(&im->refcnt), and deferring the put until after the spinlock is released.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/d4fe30f4671033a27fba077b3976dc113ffc0169
• https://git.kernel.org/stable/c/2d0effadf8d2cc9d006e4c4ab0ab6737aed28d77
• https://git.kernel.org/stable/c/40d6360ccf9bcbe17b5cb248a84e8e004aac2faa
• https://git.kernel.org/stable/c/f60ec3058a85447008b88b762c859d336163acb3
• https://git.kernel.org/stable/c/95128dc74425ec19ed4f2077ccc651e791ff4b75
• https://git.kernel.org/stable/c/3546deaa0c30a14c7cdb5dc8f2432cb428f0cd36