linux-kernel - [PATCH net] rxrpc: Fix recvmsg() unconditional requeue

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Message-ID: <3537106.1768326067@warthog.procyon.org.uk>
Date: Tue, 13 Jan 2026 17:41:07 +0000
From: David Howells <dhowells@...hat.com>
To: netdev@...r.kernel.org
cc: dhowells@...hat.com, Faith <faith@...lic.io>,
    Pumpkin Chang <pumpkin@...co.re>,
    Marc Dionne <marc.dionne@...istor.com>, Nir Ohfeld <niro@....io>,
    Willy Tarreau <w@....eu>, Eric Dumazet <edumazet@...gle.com>,
    "David S. Miller" <davem@...emloft.net>,
    Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
    Simon Horman <horms@...nel.org>, linux-afs@...ts.infradead.org,
    security@...nel.org, stable@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net] rxrpc: Fix recvmsg() unconditional requeue

    
If rxrpc_recvmsg() fails because MSG_DONTWAIT was specified but the call at
the front of the recvmsg queue already has its mutex locked, it requeues
the call - whether or not the call is already queued.  The call may be on
the queue because MSG_PEEK was also passed and so the call was not dequeued
or because the I/O thread requeued it.

The unconditional requeue may then corrupt the recvmsg queue, leading to
things like UAFs or refcount underruns.

Fix this by only requeuing the call if it isn't already on the queue - and
moving it to the front if it is already queued.

Also, MSG_PEEK doesn't dequeue the call so shouldn't call
rxrpc_notify_socket() for the call if we didn't use up all the data on the
queue, so fix that also.

Fixes: 540b1c48c37a ("rxrpc: Fix deadlock between call creation and sendmsg/recvmsg")
Reported-by: Faith <faith@...lic.io>
Reported-by: Pumpkin Chang <pumpkin@...co.re>
Signed-off-by: David Howells <dhowells@...hat.com>
Acked-by: Marc Dionne <marc.dionne@...istor.com>
cc: Nir Ohfeld <niro@....io>
cc: Willy Tarreau <w@....eu>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: Simon Horman <horms@...nel.org>
cc: linux-afs@...ts.infradead.org
cc: netdev@...r.kernel.org
cc: security@...nel.org
cc: stable@...nel.org
---
 include/trace/events/rxrpc.h |    4 ++++
 net/rxrpc/recvmsg.c          |   15 ++++++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index de6f6d25767c..869f97c9bf73 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -322,6 +322,7 @@
 	EM(rxrpc_call_put_kernel,		"PUT kernel  ") \
 	EM(rxrpc_call_put_poke,			"PUT poke    ") \
 	EM(rxrpc_call_put_recvmsg,		"PUT recvmsg ") \
+	EM(rxrpc_call_put_recvmsg_peek_nowait,	"PUT peek-nwt") \
 	EM(rxrpc_call_put_release_recvmsg_q,	"PUT rls-rcmq") \
 	EM(rxrpc_call_put_release_sock,		"PUT rls-sock") \
 	EM(rxrpc_call_put_release_sock_tba,	"PUT rls-sk-a") \
@@ -340,6 +341,9 @@
 	EM(rxrpc_call_see_input,		"SEE input   ") \
 	EM(rxrpc_call_see_notify_released,	"SEE nfy-rlsd") \
 	EM(rxrpc_call_see_recvmsg,		"SEE recvmsg ") \
+	EM(rxrpc_call_see_recvmsg_requeue,	"SEE recv-rqu") \
+	EM(rxrpc_call_see_recvmsg_requeue_first, "SEE recv-rqF") \
+	EM(rxrpc_call_see_recvmsg_requeue_move,	"SEE recv-rqM") \
 	EM(rxrpc_call_see_release,		"SEE release ") \
 	EM(rxrpc_call_see_userid_exists,	"SEE u-exists") \
 	EM(rxrpc_call_see_waiting_call,		"SEE q-conn  ") \
diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
index 7fa7e77f6bb9..2c42823f472b 100644
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -518,7 +518,8 @@ int rxrpc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 	if (rxrpc_call_has_failed(call))
 		goto call_failed;
 
-	if (!skb_queue_empty(&call->recvmsg_queue))
+	if (!(flags & MSG_PEEK) &&
+	    !skb_queue_empty(&call->recvmsg_queue))
 		rxrpc_notify_socket(call);
 	goto not_yet_complete;
 
@@ -549,11 +550,19 @@ int rxrpc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 error_requeue_call:
 	if (!(flags & MSG_PEEK)) {
 		spin_lock_irq(&rx->recvmsg_lock);
-		list_add(&call->recvmsg_link, &rx->recvmsg_q);
+		if (list_empty(&call->recvmsg_link)) {
+			list_add(&call->recvmsg_link, &rx->recvmsg_q);
+			rxrpc_see_call(call, rxrpc_call_see_recvmsg_requeue);
+		} else if (list_is_first(&call->recvmsg_link, &rx->recvmsg_q)) {
+			rxrpc_see_call(call, rxrpc_call_see_recvmsg_requeue_first);
+		} else {
+			list_move(&call->recvmsg_link, &rx->recvmsg_q);
+			rxrpc_see_call(call, rxrpc_call_see_recvmsg_requeue_move);
+		}
 		spin_unlock_irq(&rx->recvmsg_lock);
 		trace_rxrpc_recvmsg(call_debug_id, rxrpc_recvmsg_requeue, 0);
 	} else {
-		rxrpc_put_call(call, rxrpc_call_put_recvmsg);
+		rxrpc_put_call(call, rxrpc_call_put_recvmsg_peek_nowait);
 	}
 error_no_call:
 	release_sock(&rx->sk);