rxrpc: Fix potential UAF after skb_unshare() failure

cve-pre CVE-2026-43500
commit-author David Howells <dhowells@redhat.com>
commit 1f27401
upstream-diff |
	Upstream's rxrpc_input_call_event() pulls skbs from a per-call queue
	in a loop, so the unshare block sits inside that loop alongside
	rxrpc_free_skb() and saw_ack bookkeeping. This kernel's version
	receives a single skb as a function parameter and doesn't free
	it (the caller in rxrpc_io_thread() does). As such, the adapted
	unshare block wraps the existing rxrpc_input_call_packet() call
	site, creates and frees a copy when needed, and drops the loop
	and queue-drain logic that doesn't exist here.

	Upstream already had rxrpc_skb_put_call_rx and rxrpc_skb_get_call_rx
	trace constants from a prior refactor not present in this tree.
	rxrpc_skb_put_call_rx is added here since the new skb_copy path
	needs it; rxrpc_skb_get_call_rx is omitted since nothing uses it.

	Several trace constants added by upstream (rxrpc_skb_put_purge_oob,
	rxrpc_skb_put_response, rxrpc_skb_put_response_copy) don't apply
	since the code they trace doesn't exist in this kernel.

	Note, Conflict caused by 153f90a
	("rxrpc: Use ktimes for call timeout tracking and set the timer lazily").

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: 2d1faf7 ("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>
(cherry picked from commit 1f27401)
	Signed-off-by: Sultan Alsawaf <sultan@ciq.com>
	Signed-off-by: Shreeya Patel <spatel@ciq.com>
Signed-off-by: Shreeya Patel <spatel@ciq.com>

Author: kerneltoast

include/trace/events/rxrpc.h

@@ -126,8 +126,6 @@
 	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_conn_secured,		"GET conn-secd") \
 	EM(rxrpc_skb_get_conn_work,		"GET conn-work") \
 	EM(rxrpc_skb_get_last_nack,		"GET last-nack") \
@@ -139,6 +137,7 @@
 	EM(rxrpc_skb_new_error_report,		"NEW error-rpt") \
 	EM(rxrpc_skb_new_jumbo_subpacket,	"NEW jumbo-sub") \
 	EM(rxrpc_skb_new_unshared,		"NEW unshared ") \
+	EM(rxrpc_skb_put_call_rx,		"PUT call-rx  ") \
 	EM(rxrpc_skb_put_conn_secured,		"PUT conn-secd") \
 	EM(rxrpc_skb_put_conn_work,		"PUT conn-work") \
 	EM(rxrpc_skb_put_error_report,		"PUT error-rep") \
@@ -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 \

net/rxrpc/ar-internal.h

@@ -1253,7 +1253,6 @@ 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 *);

net/rxrpc/call_event.c

@@ -342,8 +342,27 @@ 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 by 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_call_rx);
+			} else {
+				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();

net/rxrpc/io_thread.c

@@ -168,13 +168,12 @@ 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));
@@ -220,25 +219,6 @@ 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:
@@ -476,7 +456,7 @@ 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);

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.
  */