netdev - [PATCH net v4] atm: mpoa: Fix UAF on qos

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Message-Id: <20251216120910.337436-1-ii4gsp@gmail.com>
Date: Tue, 16 Dec 2025 21:09:10 +0900
From: Minseong Kim <ii4gsp@...il.com>
To: netdev@...r.kernel.org
Cc: "David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	stable@...r.kernel.org
Subject: [PATCH net v4] atm: mpoa: Fix UAF on qos_head list in procfs

/proc/net/atm/mpc read-side iterates qos_head without synchronization,
while write-side can delete and free entries concurrently, leading to
use-after-free.

Protect qos_head with a mutex and ensure procfs search+delete operations
are serialized under the same lock.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@...r.kernel.org
Signed-off-by: Minseong Kim <ii4gsp@...il.com>
---
 net/atm/mpc.c       |  9 ++++++++-
 net/atm/mpc.h       |  4 ++++
 net/atm/mpoa_proc.c | 11 ++++++++++-
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/net/atm/mpc.c b/net/atm/mpc.c
index f6b447bba329..c198381281fa 100644
--- a/net/atm/mpc.c
+++ b/net/atm/mpc.c
@@ -9,6 +9,7 @@
 #include <linux/bitops.h>
 #include <linux/capability.h>
 #include <linux/seq_file.h>
+#include <linux/mutex.h>
 
 /* We are an ethernet device */
 #include <linux/if_ether.h>
@@ -122,6 +123,7 @@ static struct notifier_block mpoa_notifier = {
 
 struct mpoa_client *mpcs = NULL; /* FIXME */
 static struct atm_mpoa_qos *qos_head = NULL;
+DEFINE_MUTEX(qos_mutex); /* Protect qos_head list */
 static DEFINE_TIMER(mpc_timer, mpc_cache_check);
 
 
@@ -246,10 +248,11 @@ void atm_mpoa_disp_qos(struct seq_file *m)
 {
 	struct atm_mpoa_qos *qos;
 
-	qos = qos_head;
 	seq_printf(m, "QoS entries for shortcuts:\n");
 	seq_printf(m, "IP address\n  TX:max_pcr pcr     min_pcr max_cdv max_sdu\n  RX:max_pcr pcr     min_pcr max_cdv max_sdu\n");
 
+	mutex_lock(&qos_mutex);
+	qos = qos_head;
 	while (qos != NULL) {
 		seq_printf(m, "%pI4\n     %-7d %-7d %-7d %-7d %-7d\n     %-7d %-7d %-7d %-7d %-7d\n",
 			   &qos->ipaddr,
@@ -265,6 +268,7 @@ void atm_mpoa_disp_qos(struct seq_file *m)
 			   qos->qos.rxtp.max_sdu);
 		qos = qos->next;
 	}
+	mutex_unlock(&qos_mutex);
 }
 
 static struct net_device *find_lec_by_itfnum(int itf)
@@ -1521,8 +1525,11 @@ static void __exit atm_mpoa_cleanup(void)
 		mpc = tmp;
 	}
 
+	mutex_lock(&qos_mutex);
 	qos = qos_head;
 	qos_head = NULL;
+	mutex_unlock(&qos_mutex);
+
 	while (qos != NULL) {
 		nextqos = qos->next;
 		dprintk("freeing qos entry %p\n", qos);
diff --git a/net/atm/mpc.h b/net/atm/mpc.h
index 454abd07651a..35719b5c5e88 100644
--- a/net/atm/mpc.h
+++ b/net/atm/mpc.h
@@ -7,6 +7,7 @@
 #include <linux/atmmpc.h>
 #include <linux/skbuff.h>
 #include <linux/spinlock.h>
+#include <linux/mutex.h>
 #include "mpoa_caches.h"
 
 /* kernel -> mpc-daemon */
@@ -54,6 +55,9 @@ int atm_mpoa_delete_qos(struct atm_mpoa_qos *qos);
 struct seq_file;
 void atm_mpoa_disp_qos(struct seq_file *m);
 
+/* Protect qos_head list */
+extern struct mutex qos_mutex;
+
 #ifdef CONFIG_PROC_FS
 int mpc_proc_init(void);
 void mpc_proc_clean(void);
diff --git a/net/atm/mpoa_proc.c b/net/atm/mpoa_proc.c
index aaf64b953915..b91676187dd1 100644
--- a/net/atm/mpoa_proc.c
+++ b/net/atm/mpoa_proc.c
@@ -253,8 +253,15 @@ static int parse_qos(const char *buff)
 
 	if (sscanf(buff, "del %hhu.%hhu.%hhu.%hhu",
 			ip, ip+1, ip+2, ip+3) == 4) {
+		struct atm_mpoa_qos *entry;
+		int ret;
+
 		ipaddr = *(__be32 *)ip;
-		return atm_mpoa_delete_qos(atm_mpoa_search_qos(ipaddr));
+		mutex_lock(&qos_mutex);
+		entry = atm_mpoa_search_qos(ipaddr);
+		ret = atm_mpoa_delete_qos(entry);
+		mutex_unlock(&qos_mutex);
+		return ret;
 	}
 
 	if (sscanf(buff, "add %hhu.%hhu.%hhu.%hhu tx=%d,%d rx=tx",
@@ -277,7 +284,9 @@ static int parse_qos(const char *buff)
 		qos.txtp.max_pcr, qos.txtp.max_sdu,
 		qos.rxtp.max_pcr, qos.rxtp.max_sdu);
 
+	mutex_lock(&qos_mutex);
 	atm_mpoa_add_qos(ipaddr, &qos);
+	mutex_unlock(&qos_mutex);
 	return 1;
 }
 
-- 
2.34.1