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Sat, 04 Jul 2026 10:14:30 -0700 (PDT) Received: from fx.tailc0aff1.ts.net ([206.206.192.132]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-13b446a766asm35140615c88.7.2026.07.04.10.14.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 04 Jul 2026 10:14:29 -0700 (PDT) From: Weiming Shi To: netdev@vger.kernel.org Cc: dsahern@kernel.org, idosch@nvidia.com, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net, horms@kernel.org, xmei5@asu.edu, linux-kernel@vger.kernel.org, Weiming Shi Subject: [PATCH net] ipv4: fib: free fib_alias with kfree_rcu() on insert error path Date: Sat, 4 Jul 2026 10:14:21 -0700 Message-ID: <20260704171421.1786806-1-bestswngs@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" fib_table_insert() publishes new_fa into the leaf's fa_list with fib_insert_alias() before calling the fib entry notifiers. When a notifier fails, the error path removes new_fa with fib_remove_alias() (hlist_del_rcu) and frees it right away with kmem_cache_free(). fib_table_lookup() walks that list under rcu_read_lock() only, so a concurrent lookup that already reached new_fa keeps reading it after the free: BUG: KASAN: slab-use-after-free in fib_table_lookup (net/ipv4/fib_trie.c:1= 601) Read of size 1 at addr ffff88810676d4eb by task exploit/297 Call Trace: fib_table_lookup (net/ipv4/fib_trie.c:1601) ip_route_output_key_hash_rcu (net/ipv4/route.c:2814) ip_route_output_key_hash (net/ipv4/route.c:2705) __ip4_datagram_connect (net/ipv4/datagram.c:49) udp_connect (net/ipv4/udp.c:2144) __sys_connect (net/socket.c:2167) __x64_sys_connect (net/socket.c:2173) do_syscall_64 entry_SYSCALL_64_after_hwframe which belongs to the cache ip_fib_alias of size 56 Triggering the error path needs CAP_NET_ADMIN and a registered fib notifier that can reject a route; a netdevsim device whose IPv4 FIB resource is exhausted is enough. Free new_fa with alias_free_mem_rcu(), as fib_table_delete() already does for a fib_alias removed from the trie. Fixes: a6c76c17df02 ("ipv4: Notify route after insertion to the routing tab= le") Reported-by: Xiang Mei Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Weiming Shi --- net/ipv4/fib_trie.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index 1308213791f1..2dc87e2156d3 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -1385,7 +1385,7 @@ int fib_table_insert(struct net *net, struct fib_tabl= e *tb, out_remove_new_fa: fib_remove_alias(t, tp, l, new_fa); out_free_new_fa: - kmem_cache_free(fn_alias_kmem, new_fa); + alias_free_mem_rcu(new_fa); out: fib_release_info(fi); err: --=20 2.43.0