6.6-stable review patch. If anyone has any objections, please let me know.
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From: Gang Yan yangang@kylinos.cn
commit 443041deb5ef6a1289a99ed95015ec7442f141dc upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/mptcp/subflow.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-)
--- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -731,8 +731,6 @@ static bool subflow_hmac_valid(const str
subflow_req = mptcp_subflow_rsk(req); msk = subflow_req->msk; - if (!msk) - return false;
subflow_generate_hmac(msk->remote_key, msk->local_key, subflow_req->remote_nonce, @@ -828,12 +826,8 @@ static struct sock *subflow_syn_recv_soc
} 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: @@ -882,6 +876,13 @@ create_child: subflow_add_reset_reason(skb, MPTCP_RST_EPROHIBIT); 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;