[PATCH 6.6.y] rxrpc: Fix potential UAF after skb_unshare() failure

Sasha Levin
2026-05-03T14:06:06Z

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>
[ Relocated the unshare/skb_copy block from rxrpc_input_call_event()'s rx_queue dequeue loop to existing `if (skb) rxrpc_input_call_packet()` site, and substituted rxrpc_skb_put_call_rx with rxrpc_skb_put_input. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/trace/events/rxrpc.h | 3 +--
net/rxrpc/ar-internal.h | 1 -
net/rxrpc/call_event.c | 23 +++++++++++++++++++++--
net/rxrpc/io_thread.c | 24 ++----------------------
net/rxrpc/skbuff.c | 9 ---------
5 files changed, 24 insertions(+), 36 deletions(-)

diff --git a/include/trace/events/rxrpc.h b/include/trace/events/rxrpc.h
index 6965099dda89f..94071243c4223 100644
--- a/include/trace/events/rxrpc.h
+++ b/include/trace/events/rxrpc.h
@@ -125,8 +125,6 @@
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") \
@@ -151,6 +149,7 @@
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 f4512761f572d..1db479f3d6d3c 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -1269,7 +1269,6 @@ 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 0f78544d043be..c8a4a4c979eb6 100644
--- a/net/rxrpc/call_event.c
+++ b/net/rxrpc/call_event.c
@@ -456,8 +456,27 @@ bool rxrpc_input_call_event(struct rxrpc_call *call, struct sk_buff *skb)
resend = true;
}

- 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_input);
+ } else {
+ /* OOM - Drop the packet. */
+ rxrpc_see_skb(skb, rxrpc_skb_see_unshare_nomem);
+ }
+ } else {
+ rxrpc_input_call_packet(call, skb);
+ }
+ }

rxrpc_transmit_some_data(call);

diff --git a/net/rxrpc/io_thread.c b/net/rxrpc/io_thread.c
index 0491f2bbf61e0..f542eda13ff0b 100644
--- a/net/rxrpc/io_thread.c
+++ b/net/rxrpc/io_thread.c
@@ -167,13 +167,12 @@ 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));
@@ -219,25 +218,6 @@ 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:
@@ -479,7 +459,7 @@ 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