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Miller" , Jakub Kicinski , Paolo Abeni , Simon Horman , Alexei Starovoitov , Daniel Borkmann , bpf@vger.kernel.org (open list:BPF [L7 FRAMEWORK] (sockmap)) Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Chengfeng Ye , stable@vger.kernel.org Subject: [PATCH] bpf, sockmap: Fix cork use-after-free in tcp_bpf_sendmsg() Date: Mon, 20 Jul 2026 00:16:30 +0800 Message-ID: <20260719161630.2901208-1-nicoyip.dev@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit tcp_bpf_sendmsg() keeps msg_tx across sk_stream_wait_memory(), which drops and reacquires the socket lock. Its error path tries to decide whether msg_tx names the local temporary message by comparing it with the current value of psock->cork. This comparison is unsafe when two threads send on the same socket: Thread A Thread B msg_tx = psock->cork sk_msg_alloc() fails sk_stream_wait_memory() releases the socket lock acquires the socket lock completes the cork psock->cork = NULL frees the cork reacquires the socket lock msg_tx != psock->cork sk_msg_free(msg_tx) The stale cork is therefore mistaken for the local temporary message and freed again. KASAN reported: BUG: KASAN: slab-use-after-free in sk_msg_free+0x49/0x50 Read of size 4 at addr ffff88810c908800 by task poc/90 Call Trace: sk_msg_free+0x49/0x50 tcp_bpf_sendmsg+0x14f5/0x1cc0 __sys_sendto+0x32c/0x3a0 __x64_sys_sendto+0xdb/0x1b0 Allocated by task 89: __kasan_kmalloc+0x8f/0xa0 tcp_bpf_sendmsg+0x16b3/0x1cc0 Freed by task 91: __kasan_slab_free+0x43/0x70 kfree+0x131/0x3c0 tcp_bpf_sendmsg+0xec3/0x1cc0 msg_tx can only name the stack-local tmp or the shared cork. Test for tmp directly so a changed psock->cork cannot turn a shared message into an apparent local one. Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface") Cc: stable@vger.kernel.org Signed-off-by: Chengfeng Ye --- net/ipv4/tcp_bpf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c index 8e905b50dead..a30475afb6f8 100644 --- a/net/ipv4/tcp_bpf.c +++ b/net/ipv4/tcp_bpf.c @@ -604,7 +604,7 @@ static int tcp_bpf_sendmsg(struct sock *sk, struct msghdr *msg, size_t size) wait_for_memory: err = sk_stream_wait_memory(sk, &timeo); if (err) { - if (msg_tx && msg_tx != psock->cork) + if (msg_tx == &tmp) sk_msg_free(sk, msg_tx); goto out_err; } -- 2.43.0