In the Linux kernel, the following vulnerability has been resolved: ppp: fix race conditions in pppfillforwardpath pppfillforwardpath() has two race conditions: 1. The ppp->channels list can change between listempty() and listfirstentry(), as ppplock() is not held. If the only channel is deleted in pppdisconnectchannel(), listfirstentry() may access an empty head or a freed entry, and trigger a panic. 2. pch->chan can be NULL. When pppunregisterchannel() is called, pch->chan is set to NULL before pch is removed from ppp->channels. Fix these by using a lockless RCU approach: - Use listfirstornullrcu() to safely test and access the first list entry. - Convert list modifications on ppp->channels to their RCU variants and add synchronize_net() after removal. - Check for a NULL pch->chan before dereferencing it.