The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x 443041deb5ef6a1289a99ed95015ec7442f141dc # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025041737-entrench-peroxide-5bc7@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 443041deb5ef6a1289a99ed95015ec7442f141dc Mon Sep 17 00:00:00 2001 From: Gang Yan yangang@kylinos.cn Date: Fri, 28 Mar 2025 15:27:16 +0100 Subject: [PATCH] mptcp: fix NULL pointer in can_accept_new_subflow

When testing valkey benchmark tool with MPTCP, the kernel panics in 'mptcp_can_accept_new_subflow' because subflow_req->msk is NULL.

Call trace:

mptcp_can_accept_new_subflow (./net/mptcp/subflow.c:63 (discriminator 4)) (P) subflow_syn_recv_sock (./net/mptcp/subflow.c:854) tcp_check_req (./net/ipv4/tcp_minisocks.c:863) tcp_v4_rcv (./net/ipv4/tcp_ipv4.c:2268) ip_protocol_deliver_rcu (./net/ipv4/ip_input.c:207) ip_local_deliver_finish (./net/ipv4/ip_input.c:234) ip_local_deliver (./net/ipv4/ip_input.c:254) ip_rcv_finish (./net/ipv4/ip_input.c:449) ...

According to the debug log, the same req received two SYN-ACK in a very short time, very likely because the client retransmits the syn ack due to multiple reasons.

Even if the packets are transmitted with a relevant time interval, they can be processed by the server on different CPUs concurrently). The 'subflow_req->msk' ownership is transferred to the subflow the first, and there will be a risk of a null pointer dereference here.

This patch fixes this issue by moving the 'subflow_req->msk' under the `own_req == true` conditional.

Note that the !msk check in subflow_hmac_valid() can be dropped, because the same check already exists under the own_req mpj branch where the code has been moved to.

Fixes: 9466a1ccebbe ("mptcp: enable JOIN requests even if cookies are in use") Cc: stable@vger.kernel.org Suggested-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Gang Yan yangang@kylinos.cn Reviewed-by: Matthieu Baerts (NGI0) matttbe@kernel.org Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org Link: https://patch.msgid.link/20250328-net-mptcp-misc-fixes-6-15-v1-1-34161a482a7... Signed-off-by: Jakub Kicinski kuba@kernel.org

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index efe8d86496db..409bd415ef1d 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -754,8 +754,6 @@ static bool subflow_hmac_valid(const struct request_sock *req,

subflow_req = mptcp_subflow_rsk(req); msk = subflow_req->msk; - if (!msk) - return false;

subflow_generate_hmac(READ_ONCE(msk->remote_key), READ_ONCE(msk->local_key), @@ -850,12 +848,8 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,

} else if (subflow_req->mp_join) { mptcp_get_options(skb, &mp_opt); - if (!(mp_opt.suboptions & OPTION_MPTCP_MPJ_ACK) || - !subflow_hmac_valid(req, &mp_opt) || - !mptcp_can_accept_new_subflow(subflow_req->msk)) { - SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC); + if (!(mp_opt.suboptions & OPTION_MPTCP_MPJ_ACK)) fallback = true; - } }

create_child: @@ -905,6 +899,13 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk, goto dispose_child; }

+ if (!subflow_hmac_valid(req, &mp_opt) || + !mptcp_can_accept_new_subflow(subflow_req->msk)) { + SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC); + subflow_add_reset_reason(skb, MPTCP_RST_EPROHIBIT); + goto dispose_child; + } + /* move the msk reference ownership to the subflow */ subflow_req->msk = NULL; ctx->conn = (struct sock *)owner;