net/xen-netback: prevent UAF in xenvif_flush_hash()

net/xen-netback: prevent UAF in xenvif_flush_hash()

During the list_for_each_entry_rcu iteration call of xenvif_flush_hash,
kfree_rcu does not exist inside the rcu read critical section, so if
kfree_rcu is called when the rcu grace period ends during the iteration,
UAF occurs when accessing head->next after the entry becomes free.

Therefore, to solve this, you need to change it to list_for_each_entry_safe.

Signed-off-by: Jeongjun Park <aha310510@gmail.com>
Link: https://patch.msgid.link/20240822181109.2577354-1-aha310510@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>