Use-after-free (memory safety) in rxrpc receive path due to skb_unshare handling
Description
The commit fixes a potential use-after-free in the rxrpc receive path. Previously, when skb_unshare() could fail during in-place decryption, the parent skb pointer in the rxrpc_io_thread could be NULLed, which risked a downstream oops when trace_rxrpc_rx_done() accessed the skb. The patch moves the unsharing logic into rxrpc_input_call_event() where packets are processed for a given call, and adjusts the flow to avoid mutating the parent skb pointer on failure. It also removes the in-place unshare handling from rxrpc_input_packet(), and changes the skb handling API accordingly (no pointer-to-pointer updates). Additionally, some tracing/logging related to unshare is updated. Overall, this is a memory-safety fix in the RxRPC receive path to prevent a use-after-free/oops scenario caused by a failed skb_unshare().
Commit Details
Author: David Howells
Date: 2026-04-22 16:14 UTC
Message:
rxrpc: Fix potential UAF after skb_unshare() failure
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>
Triage Assessment
Vulnerability Type: Use-after-free
Confidence: MEDIUM
Reasoning:
The commit fixes a potential use-after-free (UAF) by correcting skb_unshare handling in the rxrpc receive path to avoid NULLing the skb pointer and subsequent oops. This is a memory-safety vulnerability that could be exploitable under certain conditions, hence considered a security-related fix.
Verification Assessment
Vulnerability Type: Use-after-free (memory safety) in rxrpc receive path due to skb_unshare handling
Confidence: MEDIUM
Affected Versions: <= v7.0-rc6
Code Diff
diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 5820d7e41ea09a..13b9d017f8e177 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -162,8 +162,6 @@
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_call_rx, "GET call-rx ") \
EM(rxrpc_skb_get_conn_secured, "GET conn-secd") \
EM(rxrpc_skb_get_conn_work, "GET conn-work") \
@@ -190,6 +188,7 @@
EM(rxrpc_skb_put_purge, "PUT purge ") \
EM(rxrpc_skb_put_purge_oob, "PUT purge-oob") \
EM(rxrpc_skb_put_response, "PUT response ") \
+ EM(rxrpc_skb_put_response_copy, "PUT resp-cpy ") \
EM(rxrpc_skb_put_rotate, "PUT rotate ") \
EM(rxrpc_skb_put_unknown, "PUT unknown ") \
EM(rxrpc_skb_see_conn_work, "SEE conn-work") \
@@ -198,6 +197,7 @@
EM(rxrpc_skb_see_recvmsg_oob, "SEE recvm-oob") \
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 96ecb83c907153..27c2aa2dd023c5 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -1486,7 +1486,6 @@ 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 fec59d9338b9fb..cc8f9dfa44e8a0 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -332,7 +332,24 @@ bool rxrpc_input_call_event(struct rxrpc_call *call)
saw_ack |= sp->hdr.type == RXRPC_PACKET_TYPE_ACK;
- rxrpc_input_call_packet(call, 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 {
+ /* OOM - Drop the packet. */
+ rxrpc_see_skb(skb, rxrpc_skb_see_unshare_nomem);
+ }
+ } else {
+ rxrpc_input_call_packet(call, skb);
+ }
rxrpc_free_skb(skb, rxrpc_skb_put_call_rx);
did_receive = true;
}
diff --git a/net/rxrpc/io_thread.c b/net/rxrpc/io_thread.c
index 69795693192521..dc5184a2fa9d1a 100644
--- a/net/rxrpc/io_thread.c
+++ b/net/rxrpc/io_thread.c
@@ -192,13 +192,12 @@ 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));
@@ -244,25 +243,6 @@ 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:
@@ -494,7 +474,7 @@ 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 3bcd6ee803960b..e2169d1a14b5fd 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.
*/