CVE-2021-47294

In the Linux kernel, the following vulnerability has been resolved:

netrom: Decrease sock refcount when sock timers expire

Commit 63346650c1a9 ("netrom: switch to sock timer API") switched to use sock timer API. It replaces modtimer() by skresettimer(), and deltimer() by skstoptimer().

Function skresettimer() will increase the refcount of sock if it is called on an inactive timer, hence, in case the timer expires, we need to decrease the refcount ourselves in the handler, otherwise, the sock refcount will be unbalanced and the sock will never be freed.