FAILED: patch "[PATCH] net: pktgen: fix proc entry use-after-free" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 817ff6efdb7f484ea547218e11e17d8e43daa3b4
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026080502-matron-stroller-b104@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 817ff6efdb7f484ea547218e11e17d8e43daa3b4 Mon Sep 17 00:00:00 2001
From: Chengfeng Ye <[email protected]>
Date: Sun, 19 Jul 2026 22:57:40 +0800
Subject: [PATCH] net: pktgen: fix proc entry use-after-free

pktgen_change_name() replaces pkt_dev->entry while holding t->if_lock. pktgen_remove_device() removes the same entry before _rem_dev_from_if_list() takes that lock.

This allows the following interleaving:

CPU 0 (NETDEV_CHANGENAME) CPU 1 (kpktgend)
if_lock(t)
proc_remove(pkt_dev->entry)

                                  proc_remove(pkt_dev->entry)

pkt_dev->entry = proc_create_data(...)
if_unlock(t)

The kthread can pass the stale proc_dir_entry to proc_remove() after the rename path has freed it. A reproducer with a widened race window reports:

  BUG: KASAN: slab-use-after-free in proc_remove+0x78/0x80
  Read of size 8 at addr ffff8881478fea70 by task kpktgend_0/67
  Call Trace:
   proc_remove+0x78/0x80
   pktgen_remove_device.isra.0+0x11c/0x4c0
   pktgen_thread_worker+0x1214/0x6bc0
   kthread+0x2c6/0x3b0
  Allocated by task 95:
   __proc_create+0x204/0x790
   proc_create_data+0x72/0xe0
   pktgen_thread_write+0xd61/0x1510
  Freed by task 28:
   kmem_cache_free+0xcb/0x3d0
   proc_free_inode+0x5b/0x80
   rcu_core+0x50a/0x1850
  The buggy address belongs to the object at ffff8881478fea00
   which belongs to the cache proc_dir_entry of size 192

Move proc_remove() into the if_lock-protected list removal helper. Keep it before list_del_rcu() to preserve the ordering required by add_device(). The rename path must then finish replacing the entry before removal, or it observes that the device is no longer on the list.

index 8e185b318288..ee64f3012321 100644
@@ -3972,6 +3972,7 @@ static void _rem_dev_from_if_list(struct pktgen_thread *t,
 	struct pktgen_dev *p;
 
 	if_lock(t);
+	proc_remove(pkt_dev->entry);
 	list_for_each_safe(q, n, &t->if_list) {
 		p = list_entry(q, struct pktgen_dev, list);
 		if (p == pkt_dev)

@@ -4001,9 +4002,6 @@ static int pktgen_remove_device(struct pktgen_thread *t,
 	 * list to determine if interface already exist, avoid race
 	 * with proc_create_data()
 	 */
-	proc_remove(pkt_dev->entry);
-
-	/* And update the thread if_list */
 	_rem_dev_from_if_list(t, pkt_dev);
 
 #ifdef CONFIG_XFRM

From: Peter Seiderer <[email protected]>

[ Upstream commit 870b856cb478bc02fffe4d89897e62c692efb09a ]

Fix checkpatch code style warnings:

WARNING: Block comments use a trailing */ on a separate line
+ * removal by worker thread */

WARNING: Block comments use * on subsequent lines
+ __u8 tos; /* six MSB of (former) IPv4 TOS
+ are for dscp codepoint */

WARNING: Block comments use a trailing */ on a separate line
+ are for dscp codepoint */

WARNING: Block comments use * on subsequent lines
+ __u8 traffic_class; /* ditto for the (former) Traffic Class in IPv6
+ (see RFC 3260, sec. 4) */

WARNING: Block comments use a trailing */ on a separate line
+ (see RFC 3260, sec. 4) */

WARNING: Block comments use * on subsequent lines
+ /* = {
+ 0x00, 0x80, 0xC8, 0x79, 0xB3, 0xCB,

WARNING: Block comments use * on subsequent lines
+ /* Field for thread to receive "posted" events terminate,
+ stop ifs etc. */

WARNING: Block comments use a trailing */ on a separate line
+ stop ifs etc. */

WARNING: Block comments should align the * on each line
+ * we go look for it ...
+*/

WARNING: Block comments use a trailing */ on a separate line
+ * we resolve the dst issue */

WARNING: Block comments use a trailing */ on a separate line
+ * with proc_create_data() */

Stable-dep-of: 817ff6efdb7f ("net: pktgen: fix proc entry use-after-free")

---
 net/core/pktgen.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

index a2838c15aa9da..c2a9cd06b766a 100644
@@ -284,7 +284,8 @@ struct pktgen_dev {
 	int pkt_overhead;	/* overhead for MPLS, VLANs, IPSEC etc */
 	int nfrags;
 	int removal_mark;	/* non-zero => the device is marked for
-				 * removal by worker thread */
+				 * removal by worker thread
+				 */
 
 	struct page *page;
 	u64 delay;		/* nano-seconds */

@@ -347,10 +348,12 @@ struct pktgen_dev {
 	__u16 udp_dst_max;	/* exclusive, dest UDP port */
 
 	/* DSCP + ECN */
-	__u8 tos;            /* six MSB of (former) IPv4 TOS
-				are for dscp codepoint */
-	__u8 traffic_class;  /* ditto for the (former) Traffic Class in IPv6
-				(see RFC 3260, sec. 4) */
+	__u8 tos;		/* six MSB of (former) IPv4 TOS
+				 * are for dscp codepoint
+				 */
+	__u8 traffic_class;	/* ditto for the (former) Traffic Class in IPv6
+				 * (see RFC 3260, sec. 4)
+				 */
 
 	/* IMIX */
 	unsigned int n_imix_entries;

@@ -390,12 +393,12 @@ struct pktgen_dev {
 
 	__u8 hh[14];
 	/* = {
-	   0x00, 0x80, 0xC8, 0x79, 0xB3, 0xCB,
-
-	   We fill in SRC address later
-	   0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-	   0x08, 0x00
-	   };
+	 * 0x00, 0x80, 0xC8, 0x79, 0xB3, 0xCB,
+	 *
+	 * We fill in SRC address later
+	 * 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	 * 0x08, 0x00
+	 * };
 	 */
 	__u16 pad;		/* pad out the hh struct to an even 16 bytes */
 

@@ -459,7 +462,8 @@ struct pktgen_thread {
 	char result[512];
 
 	/* Field for thread to receive "posted" events terminate,
-	   stop ifs etc. */
+	 * stop ifs etc.
+	 */
 
 	u32 control;
 	int cpu;

@@ -2343,7 +2347,7 @@ static inline int f_pick(struct pktgen_dev *pkt_dev)
 #ifdef CONFIG_XFRM
 /* If there was already an IPSEC SA, we keep it as is, else
  * we go look for it ...
-*/
+ */
 #define DUMMY_MARK 0
 static void get_ipsec_sa(struct pktgen_dev *pkt_dev, int flow)
 {

@@ -2647,7 +2651,8 @@ static int pktgen_output_ipsec(struct sk_buff *skb, struct pktgen_dev *pkt_dev)
 	if (!x)
 		return 0;
 	/* XXX: we dont support tunnel mode for now until
-	 * we resolve the dst issue */
+	 * we resolve the dst issue
+	 */
 	if ((x->props.mode != XFRM_MODE_TRANSPORT) && (pkt_dev->spi == 0))
 		return 0;
 

@@ -3712,7 +3717,8 @@ static int add_dev_to_thread(struct pktgen_thread *t,
 	 * userspace on another CPU than the kthread.  The if_lock()
 	 * is used here to sync with concurrent instances of
 	 * _rem_dev_from_if_list() invoked via kthread, which is also
-	 * updating the if_list */
+	 * updating the if_list
+	 */
 	if_lock(t);
 
 	if (pkt_dev->pg_thread) {

@@ -3909,7 +3915,8 @@ static int pktgen_remove_device(struct pktgen_thread *t,
 
 	/* Remove proc before if_list entry, because add_device uses
 	 * list to determine if interface already exist, avoid race
-	 * with proc_create_data() */
+	 * with proc_create_data()
+	 */
 	proc_remove(pkt_dev->entry);
 
 	/* And update the thread if_list */

2.53.0

From: Chengfeng Ye <[email protected]>

[ Upstream commit 817ff6efdb7f484ea547218e11e17d8e43daa3b4 ]

pktgen_change_name() replaces pkt_dev->entry while holding t->if_lock. pktgen_remove_device() removes the same entry before _rem_dev_from_if_list() takes that lock.

This allows the following interleaving:

CPU 0 (NETDEV_CHANGENAME) CPU 1 (kpktgend)
if_lock(t)
proc_remove(pkt_dev->entry)

                                  proc_remove(pkt_dev->entry)

pkt_dev->entry = proc_create_data(...)
if_unlock(t)

The kthread can pass the stale proc_dir_entry to proc_remove() after the rename path has freed it. A reproducer with a widened race window reports:

  BUG: KASAN: slab-use-after-free in proc_remove+0x78/0x80
  Read of size 8 at addr ffff8881478fea70 by task kpktgend_0/67
  Call Trace:
   proc_remove+0x78/0x80
   pktgen_remove_device.isra.0+0x11c/0x4c0
   pktgen_thread_worker+0x1214/0x6bc0
   kthread+0x2c6/0x3b0
  Allocated by task 95:
   __proc_create+0x204/0x790
   proc_create_data+0x72/0xe0
   pktgen_thread_write+0xd61/0x1510
  Freed by task 28:
   kmem_cache_free+0xcb/0x3d0
   proc_free_inode+0x5b/0x80
   rcu_core+0x50a/0x1850
  The buggy address belongs to the object at ffff8881478fea00
   which belongs to the cache proc_dir_entry of size 192

Move proc_remove() into the if_lock-protected list removal helper. Keep it before list_del_rcu() to preserve the ordering required by add_device(). The rename path must then finish replacing the entry before removal, or it observes that the device is no longer on the list.

---
 net/core/pktgen.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

index c2a9cd06b766a..23ec71a882906 100644
@@ -3888,6 +3888,7 @@ static void _rem_dev_from_if_list(struct pktgen_thread *t,
 	struct pktgen_dev *p;
 
 	if_lock(t);
+	proc_remove(pkt_dev->entry);
 	list_for_each_safe(q, n, &t->if_list) {
 		p = list_entry(q, struct pktgen_dev, list);
 		if (p == pkt_dev)

@@ -3917,9 +3918,6 @@ static int pktgen_remove_device(struct pktgen_thread *t,
 	 * list to determine if interface already exist, avoid race
 	 * with proc_create_data()
 	 */
-	proc_remove(pkt_dev->entry);
-
-	/* And update the thread if_list */
 	_rem_dev_from_if_list(t, pkt_dev);
 
 #ifdef CONFIG_XFRM

2.53.0