ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer()

Overview

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

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 2d0effadf8d2cc9d006e4c4ab0ab6737aed28d77
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 40d6360ccf9bcbe17b5cb248a84e8e004aac2faa
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f60ec3058a85447008b88b762c859d336163acb3
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 95128dc74425ec19ed4f2077ccc651e791ff4b75
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 3546deaa0c30a14c7cdb5dc8f2432cb428f0cd36
• Linux 2.6.12

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.