[PATCH 5.10.y] rxrpc: Fix recvmsg() unconditional requeue

[PATCH 5.10.y] rxrpc: Fix recvmsg() unconditional requeue

[Jay Wang]

From: David Howells <dhowells@redhat.com>

[ Upstream commit 2c28769a51deb6022d7fbd499987e237a01dd63a ]

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.  If we don't queue
it, we have to put the ref we obtained by dequeuing it.

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@zellic.io>
Reported-by: Pumpkin Chang <pumpkin@devco.re>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Cc: stable@vger.kernel.org
[Adapted to 5.10: use write_lock_bh/write_unlock_bh, trace_rxrpc_call
 directly for see-call tracing, 5.10 trace enum naming convention, and
 added entries to both plain enum and EM() macro list.]
Signed-off-by: Jay Wang <wanjay@amazon.com>
---
 include/trace/events/rxrpc.h | 8 ++++++++
 net/rxrpc/recvmsg.c          | 20 ++++++++++++++++----
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -93,9 +93,13 @@ enum rxrpc_call_trace {
 	rxrpc_call_put_notimer,
 	rxrpc_call_put_timer,
 	rxrpc_call_put_userid,
+	rxrpc_call_put_recvmsg_peek_nowait,
 	rxrpc_call_queued,
 	rxrpc_call_queued_ref,
 	rxrpc_call_release,
+	rxrpc_call_see_recvmsg_requeue,
+	rxrpc_call_see_recvmsg_requeue_first,
+	rxrpc_call_see_recvmsg_requeue_move,
 	rxrpc_call_seen,
 };
 
@@ -291,9 +295,13 @@ enum rxrpc_tx_point {
 	EM(rxrpc_call_put_notimer,		"PnT") \
 	EM(rxrpc_call_put_timer,		"PTM") \
 	EM(rxrpc_call_put_userid,		"Pus") \
+	EM(rxrpc_call_put_recvmsg_peek_nowait,	"PpN") \
 	EM(rxrpc_call_queued,			"QUE") \
 	EM(rxrpc_call_queued_ref,		"QUR") \
 	EM(rxrpc_call_release,			"RLS") \
+	EM(rxrpc_call_see_recvmsg_requeue,	"SrQ") \
+	EM(rxrpc_call_see_recvmsg_requeue_first,"SrF") \
+	EM(rxrpc_call_see_recvmsg_requeue_move,	"SrM") \
 	E_(rxrpc_call_seen,			"SEE")
 
 #define rxrpc_transmit_traces \
diff --git a/net/rxrpc/recvmsg.c b/net/rxrpc/recvmsg.c
--- a/net/rxrpc/recvmsg.c
+++ b/net/rxrpc/recvmsg.c
@@ -607,7 +607,8 @@ int rxrpc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 
 		if (after(call->rx_top, call->rx_hard_ack) &&
 		    call->rxtx_buffer[(call->rx_hard_ack + 1) & RXRPC_RXTX_BUFF_MASK])
-			rxrpc_notify_socket(call);
+			if (!(flags & MSG_PEEK))
+				rxrpc_notify_socket(call);
 		break;
 	default:
 		ret = 0;
@@ -642,11 +643,24 @@ int rxrpc_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 error_requeue_call:
 	if (!(flags & MSG_PEEK)) {
 		write_lock_bh(&rx->recvmsg_lock);
-		list_add(&call->recvmsg_link, &rx->recvmsg_q);
-		write_unlock_bh(&rx->recvmsg_lock);
+		if (list_empty(&call->recvmsg_link)) {
+			list_add(&call->recvmsg_link, &rx->recvmsg_q);
+			trace_rxrpc_call(call->debug_id,
+					 rxrpc_call_see_recvmsg_requeue,
+					 refcount_read(&call->ref),
+					 __builtin_return_address(0), NULL);
+			write_unlock_bh(&rx->recvmsg_lock);
+		} else if (list_is_first(&call->recvmsg_link, &rx->recvmsg_q)) {
+			write_unlock_bh(&rx->recvmsg_lock);
+			rxrpc_put_call(call, rxrpc_call_see_recvmsg_requeue_first);
+		} else {
+			list_move(&call->recvmsg_link, &rx->recvmsg_q);
+			write_unlock_bh(&rx->recvmsg_lock);
+			rxrpc_put_call(call, rxrpc_call_see_recvmsg_requeue_move);
+		}
 		trace_rxrpc_recvmsg(call, rxrpc_recvmsg_requeue, 0, 0, 0, 0);
 	} else {
-		rxrpc_put_call(call, rxrpc_call_put);
+		rxrpc_put_call(call, rxrpc_call_put_recvmsg_peek_nowait);
 	}
 error_no_call:
 	release_sock(&rx->sk);
-- 
2.43.0

Re: [PATCH 5.10.y] rxrpc: Fix recvmsg() unconditional requeue

[Greg KH]

On Wed, Apr 22, 2026 at 10:24:32PM +0000, Jay Wang wrote:
> From: David Howells <dhowells@redhat.com>
> 
> [ Upstream commit 2c28769a51deb6022d7fbd499987e237a01dd63a ]
> 
> 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.

Why did you reformat the changelog text?  Please do not.

thanks,

greg k-h

Re: [PATCH 5.10.y] rxrpc: Fix recvmsg() unconditional requeue

[Sasha Levin]

On Wed, Apr 22, 2026 at 10:24:32PM +0000, Jay Wang wrote:
> From: David Howells <dhowells@redhat.com>
>
> [ Upstream commit 2c28769a51deb6022d7fbd499987e237a01dd63a ]
>
> 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.

Queued for 5.10, thanks.

--
Thanks,
Sasha