[PATCH 6.12.y] rxrpc: Fix potential UAF after skb_unshare() failure

[Sasha Levin <sashal@kernel.org>]

From: David Howells <dhowells@redhat.com>

[ Upstream commit 1f2740150f904bfa60e4bad74d65add3ccb5e7f8 ]

If skb_unshare() fails to unshare a packet due to allocation failure in
rxrpc_input_packet(), the skb pointer in the parent (rxrpc_io_thread())
will be NULL'd out.  This will likely cause the call to
trace_rxrpc_rx_done() to oops.

Fix this by moving the unsharing down to where rxrpc_input_call_event()
calls rxrpc_input_call_packet().  There are a number of places prior to
that where we ignore DATA packets for a variety of reasons (such as the
call already being complete) for which an unshare is then avoided.

And with that, rxrpc_input_packet() doesn't need to take a pointer to the
pointer to the packet, so change that to just a pointer.

Fixes: 2d1faf7a0ca3 ("rxrpc: Simplify skbuff accounting in receive path")
Closes: https://sashiko.dev/#/patchset/20260408121252.2249051-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: Simon Horman <horms@kernel.org>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260422161438.2593376-4-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ adapted to per-skb rxrpc_input_call_event() signature ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/trace/events/rxrpc.h |  4 ++--
 net/rxrpc/ar-internal.h      |  1 -
 net/rxrpc/call_event.c       | 24 ++++++++++++++++++++++--
 net/rxrpc/io_thread.c        | 24 ++----------------------
 net/rxrpc/skbuff.c           |  9 ---------
 5 files changed, 26 insertions(+), 36 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 3eb806f7bc6a5..b6669a576fd58 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -126,8 +126,7 @@
 	E_(rxrpc_call_poke_timer_now,		"Timer-now")
 
 #define rxrpc_skb_traces \
-	EM(rxrpc_skb_eaten_by_unshare,		"ETN unshare  ") \
-	EM(rxrpc_skb_eaten_by_unshare_nomem,	"ETN unshar-nm") \
+	EM(rxrpc_skb_get_call_rx,		"GET call-rx  ") \
 	EM(rxrpc_skb_get_conn_secured,		"GET conn-secd") \
 	EM(rxrpc_skb_get_conn_work,		"GET conn-work") \
 	EM(rxrpc_skb_get_last_nack,		"GET last-nack") \
@@ -152,6 +151,7 @@
 	EM(rxrpc_skb_see_recvmsg,		"SEE recvmsg  ") \
 	EM(rxrpc_skb_see_reject,		"SEE reject   ") \
 	EM(rxrpc_skb_see_rotate,		"SEE rotate   ") \
+	EM(rxrpc_skb_see_unshare_nomem,		"SEE unshar-nm") \
 	E_(rxrpc_skb_see_version,		"SEE version  ")
 
 #define rxrpc_local_traces \
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 1494d162444dd..63cd5217b4ee3 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -1260,7 +1260,6 @@ int rxrpc_server_keyring(struct rxrpc_sock *, sockptr_t, int);
 void rxrpc_kernel_data_consumed(struct rxrpc_call *, struct sk_buff *);
 void rxrpc_new_skb(struct sk_buff *, enum rxrpc_skb_trace);
 void rxrpc_see_skb(struct sk_buff *, enum rxrpc_skb_trace);
-void rxrpc_eaten_skb(struct sk_buff *, enum rxrpc_skb_trace);
 void rxrpc_get_skb(struct sk_buff *, enum rxrpc_skb_trace);
 void rxrpc_free_skb(struct sk_buff *, enum rxrpc_skb_trace);
 void rxrpc_purge_queue(struct sk_buff_head *);
diff --git a/net/rxrpc/call_event.c b/net/rxrpc/call_event.c
index 7bbb685047667..81d77b7449f7e 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -342,8 +342,28 @@ bool rxrpc_input_call_event(struct rxrpc_call *call, struct sk_buff *skb)
 	if (skb && skb->mark == RXRPC_SKB_MARK_ERROR)
 		goto out;
 
-	if (skb)
-		rxrpc_input_call_packet(call, skb);
+	if (skb) {
+		struct rxrpc_skb_priv *sp = rxrpc_skb(skb);
+
+		if (sp->hdr.securityIndex != 0 &&
+		    skb_cloned(skb)) {
+			/* Unshare the packet so that it can be modified for
+			 * in-place decryption.
+			 */
+			struct sk_buff *nskb = skb_copy(skb, GFP_ATOMIC);
+
+			if (nskb) {
+				rxrpc_new_skb(nskb, rxrpc_skb_new_unshared);
+				rxrpc_input_call_packet(call, nskb);
+				rxrpc_free_skb(nskb, rxrpc_skb_put_input);
+			} else {
+				/* OOM - Drop the packet. */
+				rxrpc_see_skb(skb, rxrpc_skb_see_unshare_nomem);
+			}
+		} else {
+			rxrpc_input_call_packet(call, skb);
+		}
+	}
 
 	/* If we see our async-event poke, check for timeout trippage. */
 	now = ktime_get_real();
diff --git a/net/rxrpc/io_thread.c b/net/rxrpc/io_thread.c
index 83c5f715c6b73..8270cac0488d9 100644
--- a/net/rxrpc/io_thread.c
+++ b/net/rxrpc/io_thread.c
@@ -178,13 +178,12 @@ static bool rxrpc_extract_abort(struct sk_buff *skb)
 /*
  * Process packets received on the local endpoint
  */
-static bool rxrpc_input_packet(struct rxrpc_local *local, struct sk_buff **_skb)
+static bool rxrpc_input_packet(struct rxrpc_local *local, struct sk_buff *skb)
 {
 	struct rxrpc_connection *conn;
 	struct sockaddr_rxrpc peer_srx;
 	struct rxrpc_skb_priv *sp;
 	struct rxrpc_peer *peer = NULL;
-	struct sk_buff *skb = *_skb;
 	bool ret = false;
 
 	skb_pull(skb, sizeof(struct udphdr));
@@ -230,25 +229,6 @@ static bool rxrpc_input_packet(struct rxrpc_local *local, struct sk_buff **_skb)
 			return rxrpc_bad_message(skb, rxrpc_badmsg_zero_call);
 		if (sp->hdr.seq == 0)
 			return rxrpc_bad_message(skb, rxrpc_badmsg_zero_seq);
-
-		/* Unshare the packet so that it can be modified for in-place
-		 * decryption.
-		 */
-		if (sp->hdr.securityIndex != 0) {
-			skb = skb_unshare(skb, GFP_ATOMIC);
-			if (!skb) {
-				rxrpc_eaten_skb(*_skb, rxrpc_skb_eaten_by_unshare_nomem);
-				*_skb = NULL;
-				return just_discard;
-			}
-
-			if (skb != *_skb) {
-				rxrpc_eaten_skb(*_skb, rxrpc_skb_eaten_by_unshare);
-				*_skb = skb;
-				rxrpc_new_skb(skb, rxrpc_skb_new_unshared);
-				sp = rxrpc_skb(skb);
-			}
-		}
 		break;
 
 	case RXRPC_PACKET_TYPE_CHALLENGE:
@@ -490,7 +470,7 @@ int rxrpc_io_thread(void *data)
 			switch (skb->mark) {
 			case RXRPC_SKB_MARK_PACKET:
 				skb->priority = 0;
-				if (!rxrpc_input_packet(local, &skb))
+				if (!rxrpc_input_packet(local, skb))
 					rxrpc_reject_packet(local, skb);
 				trace_rxrpc_rx_done(skb->mark, skb->priority);
 				rxrpc_free_skb(skb, rxrpc_skb_put_input);
diff --git a/net/rxrpc/skbuff.c b/net/rxrpc/skbuff.c
index 3bcd6ee803960..e2169d1a14b5f 100644
--- a/net/rxrpc/skbuff.c
+++ b/net/rxrpc/skbuff.c
@@ -46,15 +46,6 @@ void rxrpc_get_skb(struct sk_buff *skb, enum rxrpc_skb_trace why)
 	skb_get(skb);
 }
 
-/*
- * Note the dropping of a ref on a socket buffer by the core.
- */
-void rxrpc_eaten_skb(struct sk_buff *skb, enum rxrpc_skb_trace why)
-{
-	int n = atomic_inc_return(&rxrpc_n_rx_skbs);
-	trace_rxrpc_skb(skb, 0, n, why);
-}
-
 /*
  * Note the destruction of a socket buffer.
  */
-- 
2.53.0