net: decrease cached dst counters in dst_release

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: decrease cached dst counters in dst_release Upstream fix ac888d58869b ("net: do not delay dst_entries_add() in dst_release()") moved decrementing the dst count from dst_destroy to dst_release to avoid accessing already freed data in case of netns dismantle. However in case CONFIG_DST_CACHE is enabled and OvS+tunnels are used, this fix is incomplete as the same issue will be seen for cached dsts: Unable to handle kernel paging request at virtual address ffff5aabf6b5c000 Call trace: percpu_counter_add_batch+0x3c/0x160 (P) dst_release+0xec/0x108 dst_cache_destroy+0x68/0xd8 dst_destroy+0x13c/0x168 dst_destroy_rcu+0x1c/0xb0 rcu_do_batch+0x18c/0x7d0 rcu_core+0x174/0x378 rcu_core_si+0x18/0x30 Fix this by invalidating the cache, and thus decrementing cached dst counters, in dst_release too.

References

• https://git.kernel.org/stable/c/ccc331fd5bcae131d2627d5ef099d4a1f6540aea
• https://git.kernel.org/stable/c/92a5c18513117be69bc00419dd1724c1940f8fcd
• https://git.kernel.org/stable/c/836415a8405c9665ae55352fc5ba865c242f5e4f
• https://git.kernel.org/stable/c/e833e7ad64eb2f63867f65303be49ca30ee8819e
• https://git.kernel.org/stable/c/3a0a3ff6593d670af2451ec363ccb7b18aec0c0a