kobject: fix uevent socket use-after-free on net namespace delete

PATCH Superseded Adarsh Das 2 participants 11 messages Sep 17 – Sep 18

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Adarsh Das

author

2026-09-17 14:42 UTC #0 lore raw

PATCH 1/1 kobject: fix uevent socket use-after-free on net namespace delete

When a network namespace is deleted, we free its uevent socket. But sometimes a device in that namespace is still being removed and tries to send a uevent through that socket. The socket is already freed, so KASAN reports a use-after-free.

This patch attempts the fix of taking a lock around both the send path and the free path, and clear the pointer before freeing so nobody uses it after free.

Reported-by syzbot <[email protected]>

Link https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0

Signed-off-by Adarsh Das <[email protected]>

---
 lib/kobject_uevent.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

lib/kobject_uevent.c +17 -7

index ddbc4d7482d2..ecba33abb6b1 100644
@@ -411,9 +411,15 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 						    devpath);
 	else {
 		const struct net *net = container_of(ns, struct net, ns);
+		struct uevent_sock *ue_sk;
 
-		ret = uevent_net_broadcast_tagged(net->uevent_sock->sk, env,
-						  action_string, devpath);
+		mutex_lock(&uevent_sock_mutex);
+		ue_sk = net->uevent_sock;
+		if (ue_sk && ue_sk->sk)
+			ret = uevent_net_broadcast_tagged(ue_sk->sk, env,
+							  action_string,
+							  devpath);
+		mutex_unlock(&uevent_sock_mutex);
 	}
 #endif

@@ -804,13 +810,17 @@ static int uevent_net_init(struct net *net)
 
 static void uevent_net_exit(struct net *net)
 {
-	struct uevent_sock *ue_sk = net->uevent_sock;
+	struct uevent_sock *ue_sk;
 
-	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
-		mutex_lock(&uevent_sock_mutex);
+	mutex_lock(&uevent_sock_mutex);
+	ue_sk = net->uevent_sock;
+	net->uevent_sock = NULL;
+	if (ue_sk && sock_net(ue_sk->sk)->user_ns == &init_user_ns)
 		list_del(&ue_sk->list);
-		mutex_unlock(&uevent_sock_mutex);
-	}
+	mutex_unlock(&uevent_sock_mutex);
+
+	if (!ue_sk)
+		return;
 
 	netlink_kernel_release(ue_sk->sk);
 	kfree(ue_sk);

Signature · 1 line

2.55.0

Greg KH

maintainer

2026-09-17 14:53 UTC #1 lore raw

Quoted 9 lines · Adarsh Das

When a network namespace is deleted, we free its uevent socket. But sometimes a device in that namespace is still being removed and tries to send a uevent through that socket. The socket is already freed, so KASAN reports a use-after-free.
This patch attempts the fix of taking a lock around both the send path and the free path, and clear the pointer before freeing so nobody uses it after free.

Quoted 6 lines

Reported-by syzbot <[email protected]>
Link https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
Signed-off-by Adarsh Das <[email protected]>
---
 lib/kobject_uevent.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

Did you forget an Assisted-by: tag?

How was this tested?

thanks,

greg k-h

Adarsh Das

author

2026-09-17 15:18 UTC #2 lore raw

Hi,

Sorry, I wasn't aware of the Assisted-by tag before. Should I send a V2 with it?

For testing I ran syzbot's C repro with -smp 4 on master, with multiple parallel instances of the repro. I was able to reproduce the bug:

  BUG: KASAN: slab-use-after-free in kobject_uevent_env+
  Read of size 8 at addr ffff88800fa7f090 by task kworker/u16:5
  CPU: 3
  Workqueue: ib-unreg-wq ib_unregister_work
  Call Trace:
    kasan_report
    kobject_uevent_env+0xc71/0xd90
    device_del+0x7c7/0xcf0
    disable_device+0x1d2/0x260
    __ib_unregister_device+0x26b/0x400
    ib_unregister_work+0x19/0x30
    worker_thread
    kthread
  Allocated by task 498:
    uevent_net_init+0xe5/0x340
    setup_net
    copy_net_ns
    unshare_nsproxy_namespaces
    ksys_unshare
  Freed by task 63:
    kfree
    ops_undo_list
    cleanup_net
    worker_thread
  The buggy address belongs to the cache kmalloc-32 of size 32

With this patch applied, I ran the same repro repeatedly (including parallel runs) and did not see the KASAN error anymore.

Greg KH

maintainer

2026-09-17 16:09 UTC #3 lore raw

A: http://en.wikipedia.org/wiki/Top_post
Q: Were do I find info about this thing called top-posting?
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

Quoted 4 lines · Adarsh Das

Hi,
Sorry, I wasn't aware of the Assisted-by tag before. Should I send a V2 with it?

Please do.

Quoted 30 lines

For testing I ran syzbot's C repro with -smp 4 on master, with multiple parallel instances of the repro. I was able to reproduce the bug:

  BUG: KASAN: slab-use-after-free in kobject_uevent_env+
  Read of size 8 at addr ffff88800fa7f090 by task kworker/u16:5
  CPU: 3
  Workqueue: ib-unreg-wq ib_unregister_work
  Call Trace:
    kasan_report
    kobject_uevent_env+0xc71/0xd90
    device_del+0x7c7/0xcf0
    disable_device+0x1d2/0x260
    __ib_unregister_device+0x26b/0x400
    ib_unregister_work+0x19/0x30
    worker_thread
    kthread
  Allocated by task 498:
    uevent_net_init+0xe5/0x340
    setup_net
    copy_net_ns
    unshare_nsproxy_namespaces
    ksys_unshare
  Freed by task 63:
    kfree
    ops_undo_list
    cleanup_net
    worker_thread
  The buggy address belongs to the cache kmalloc-32 of size 32

Quoted 2 lines

With this patch applied, I ran the same repro repeatedly (including parallel runs) and did not see the KASAN error anymore.

Did syzbot also test this?

And I have no context here at all, sorry, please realize that some of us get 1000+ emails a day...

thanks,

greg k-h

Adarsh Das

author

2026-09-17 17:08 UTC #4 lore raw

PATCH v2 1/1 kobject: fix uevent socket use-after-free on net namespace delete

In reply to Adarsh Das

Hi Greg,

v2 adds Assisted-by and Tested-by tags as requested.

Local testing: syzbot C repro on unfixed master with -smp 4 (parallel runs) reproduced the KASAN UAF. With patch applied, no KASAN.

Syzbot testing: #syz test with patch on upstream — Result OK
https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0

Adarsh

Adarsh Das

author

2026-09-17 17:08 UTC #5 lore raw

PATCH v2 1/1 kobject: fix uevent socket use-after-free on net namespace delete

In reply to Adarsh Das

This patch attempts the fix of taking a lock around both the send path and the free path, and clear the pointer before freeing so nobody uses it after free.

Reported-by syzbot <[email protected]>

Link https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0

Tested-by syzbot <[email protected]>

Tested-by Adarsh Das <[email protected]>

Assisted-by Cursor AI

Signed-off-by Adarsh Das <[email protected]>

---
 lib/kobject_uevent.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

lib/kobject_uevent.c +17 -7

index ddbc4d7482d2..ecba33abb6b1 100644
@@ -411,9 +411,15 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 						    devpath);
 	else {
 		const struct net *net = container_of(ns, struct net, ns);
+		struct uevent_sock *ue_sk;
 
-		ret = uevent_net_broadcast_tagged(net->uevent_sock->sk, env,
-						  action_string, devpath);
+		mutex_lock(&uevent_sock_mutex);
+		ue_sk = net->uevent_sock;
+		if (ue_sk && ue_sk->sk)
+			ret = uevent_net_broadcast_tagged(ue_sk->sk, env,
+							  action_string,
+							  devpath);
+		mutex_unlock(&uevent_sock_mutex);
 	}
 #endif

@@ -804,13 +810,17 @@ static int uevent_net_init(struct net *net)
 
 static void uevent_net_exit(struct net *net)
 {
-	struct uevent_sock *ue_sk = net->uevent_sock;
+	struct uevent_sock *ue_sk;
 
-	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
-		mutex_lock(&uevent_sock_mutex);
+	mutex_lock(&uevent_sock_mutex);
+	ue_sk = net->uevent_sock;
+	net->uevent_sock = NULL;
+	if (ue_sk && sock_net(ue_sk->sk)->user_ns == &init_user_ns)
 		list_del(&ue_sk->list);
-		mutex_unlock(&uevent_sock_mutex);
-	}
+	mutex_unlock(&uevent_sock_mutex);
+
+	if (!ue_sk)
+		return;
 
 	netlink_kernel_release(ue_sk->sk);
 	kfree(ue_sk);

Signature · 1 line

2.55.0

Greg KH

maintainer

2026-09-17 19:11 UTC #6 lore raw

Quoted 24 lines · Adarsh Das

When a network namespace is deleted, we free its uevent socket. But sometimes a device in that namespace is still being removed and tries to send a uevent through that socket. The socket is already freed, so KASAN reports a use-after-free.
This patch attempts the fix of taking a lock around both the send path and the free path, and clear the pointer before freeing so nobody uses it after free.
Reported-by syzbot <[email protected]>
Link https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
Tested-by syzbot <[email protected]>
Tested-by Adarsh Das <[email protected]>
Assisted-by Cursor AI
Signed-off-by Adarsh Das <[email protected]>
---
 lib/kobject_uevent.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)
lib/kobject_uevent.c +0 -0
index ddbc4d7482d2..ecba33abb6b1 100644

lib/kobject_uevent.c static int kobject_uevent_net_broadcast(struct kobject *kobj, · line 416

Quoted 8 lines

lib/kobject_uevent.c +2 -2

@@ -411,9 +411,15 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 						    devpath);
 	else {
 		const struct net *net = container_of(ns, struct net, ns);
+		struct uevent_sock *ue_sk;
 
-		ret = uevent_net_broadcast_tagged(net->uevent_sock->sk, env,
-						  action_string, devpath);
+		mutex_lock(&uevent_sock_mutex);

Can't you use a guard to make this a lot cleaner?

thanks,

greg k-h

Adarsh Das

author

2026-09-18 06:09 UTC #7 lore raw

PATCH v3 1/1 kobject: fix uevent socket use-after-free on net namespace delete

This patch attempts the fix of taking a lock around both the send path and the free path, and clear the pointer before freeing so nobody uses it after free.

Reported-by syzbot <[email protected]>

Link https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0

Tested-by syzbot <[email protected]>

Tested-by Adarsh Das <[email protected]>

Assisted-by LLM

Signed-off-by Adarsh Das <[email protected]>

---
 lib/kobject_uevent.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

lib/kobject_uevent.c +19 -8

index ddbc4d7482d2..cb674c2c3432 100644
@@ -13,6 +13,7 @@
  *	Greg Kroah-Hartman	<[email protected]>
  */
 
+#include <linux/cleanup.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/kobject.h>

@@ -411,9 +412,14 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 						    devpath);
 	else {
 		const struct net *net = container_of(ns, struct net, ns);
-
-		ret = uevent_net_broadcast_tagged(net->uevent_sock->sk, env,
-						  action_string, devpath);
+		struct uevent_sock *ue_sk;
+
+		guard(mutex)(&uevent_sock_mutex);
+		ue_sk = net->uevent_sock;
+		if (ue_sk && ue_sk->sk)
+			ret = uevent_net_broadcast_tagged(ue_sk->sk, env,
+							  action_string,
+							  devpath);
 	}
 #endif

@@ -804,14 +810,19 @@ static int uevent_net_init(struct net *net)
 
 static void uevent_net_exit(struct net *net)
 {
-	struct uevent_sock *ue_sk = net->uevent_sock;
+	struct uevent_sock *ue_sk;
 
-	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
-		mutex_lock(&uevent_sock_mutex);
-		list_del(&ue_sk->list);
-		mutex_unlock(&uevent_sock_mutex);
+	{
+		guard(mutex)(&uevent_sock_mutex);
+		ue_sk = net->uevent_sock;
+		net->uevent_sock = NULL;
+		if (ue_sk && sock_net(ue_sk->sk)->user_ns == &init_user_ns)
+			list_del(&ue_sk->list);
 	}
 
+	if (!ue_sk)
+		return;
+
 	netlink_kernel_release(ue_sk->sk);
 	kfree(ue_sk);
 }

Signature · 1 line

2.55.0

Greg KH

maintainer

2026-09-18 08:16 UTC #8 lore raw

Quoted 77 lines · Adarsh Das

This patch attempts the fix of taking a lock around both the send path and the free path, and clear the pointer before freeing so nobody uses it after free.

Reported-by syzbot <[email protected]>

Link https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0

Tested-by syzbot <[email protected]>

Tested-by Adarsh Das <[email protected]>

Assisted-by LLM

Signed-off-by Adarsh Das <[email protected]>

---
 lib/kobject_uevent.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

lib/kobject_uevent.c +19 -8

index ddbc4d7482d2..cb674c2c3432 100644
@@ -13,6 +13,7 @@
  *	Greg Kroah-Hartman	<[email protected]>
  */
 
+#include <linux/cleanup.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/kobject.h>

@@ -411,9 +412,14 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 						    devpath);
 	else {
 		const struct net *net = container_of(ns, struct net, ns);
-
-		ret = uevent_net_broadcast_tagged(net->uevent_sock->sk, env,
-						  action_string, devpath);
+		struct uevent_sock *ue_sk;
+
+		guard(mutex)(&uevent_sock_mutex);
+		ue_sk = net->uevent_sock;
+		if (ue_sk && ue_sk->sk)
+			ret = uevent_net_broadcast_tagged(ue_sk->sk, env,
+							  action_string,
+							  devpath);
 	}
 #endif

@@ -804,14 +810,19 @@ static int uevent_net_init(struct net *net)
 
 static void uevent_net_exit(struct net *net)
 {
-	struct uevent_sock *ue_sk = net->uevent_sock;
+	struct uevent_sock *ue_sk;
 
-	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
-		mutex_lock(&uevent_sock_mutex);
-		list_del(&ue_sk->list);
-		mutex_unlock(&uevent_sock_mutex);
+	{
+		guard(mutex)(&uevent_sock_mutex);
+		ue_sk = net->uevent_sock;
+		net->uevent_sock = NULL;
+		if (ue_sk && sock_net(ue_sk->sk)->user_ns == &init_user_ns)
+			list_del(&ue_sk->list);
 	}
 
+	if (!ue_sk)
+		return;
+
 	netlink_kernel_release(ue_sk->sk);
 	kfree(ue_sk);
 }

Signature · 1 line

2.55.0

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman. You have sent him a patch that has triggered this response. He used to manually respond to these common problems, but in order to save his sanity (he kept writing the same thing over and over, yet to different people), I was created. Hopefully you will not take offence and will fix the problem in your patch and resubmit it so that it can be accepted into the Linux kernel tree.

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If you wish to discuss this problem further, or you have questions about how to resolve this issue, please feel free to respond to this email and Greg will reply once he has dug out from the pending patches received from other developers.

thanks,

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Greg KH

maintainer

2026-09-18 08:16 UTC #9 lore raw

In reply to Adarsh Das

lib/kobject_uevent.c static int uevent_net_init(struct net *net) · line 816

Quoted 13 lines · Adarsh Das

lib/kobject_uevent.c +3 -5

@@ -804,14 +810,19 @@ static int uevent_net_init(struct net *net)
 
 static void uevent_net_exit(struct net *net)
 {
-	struct uevent_sock *ue_sk = net->uevent_sock;
+	struct uevent_sock *ue_sk;
 
-	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
-		mutex_lock(&uevent_sock_mutex);
-		list_del(&ue_sk->list);
-		mutex_unlock(&uevent_sock_mutex);
+	{
+		guard(mutex)(&uevent_sock_mutex);

LLMs don't know how to use these correctly, shouldn't this just be a scoped_guard()? No extra {} like that please, it's not normal kernel coding style at all.

thanks,

greg k-h

Adarsh Das

author

2026-09-18 09:43 UTC #10 lore raw

PATCH v4 1/1 kobject: fix uevent socket use-after-free on net namespace delete

Take a lock around both the send path and the free path, and clear the pointer before freeing so nobody uses it after free.

Reported-and-tested-by [email protected]

Tested-by Adarsh Das <[email protected]>

Assisted-by LLM

Link https://lore.kernel.org/all/[email protected]/ open here

Signed-off-by Adarsh Das <[email protected]>

---
v4:
- Use scoped_guard(mutex) instead of block in uevent_net_exit
v3:
- Use guard(mutex) per review
v2:
- Add Assisted-by and Tested-by tags per review

 lib/kobject_uevent.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

lib/kobject_uevent.c +18 -8

index ddbc4d7482d2..14e2e15d4ea7 100644
@@ -13,6 +13,7 @@
  *	Greg Kroah-Hartman	<[email protected]>
  */
 
+#include <linux/cleanup.h>
 #include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/kobject.h>

@@ -411,9 +412,14 @@ static int kobject_uevent_net_broadcast(struct kobject *kobj,
 						    devpath);
 	else {
 		const struct net *net = container_of(ns, struct net, ns);
-
-		ret = uevent_net_broadcast_tagged(net->uevent_sock->sk, env,
-						  action_string, devpath);
+		struct uevent_sock *ue_sk;
+
+		guard(mutex)(&uevent_sock_mutex);
+		ue_sk = net->uevent_sock;
+		if (ue_sk && ue_sk->sk)
+			ret = uevent_net_broadcast_tagged(ue_sk->sk, env,
+							  action_string,
+							  devpath);
 	}
 #endif

@@ -804,14 +810,18 @@ static int uevent_net_init(struct net *net)
 
 static void uevent_net_exit(struct net *net)
 {
-	struct uevent_sock *ue_sk = net->uevent_sock;
+	struct uevent_sock *ue_sk;
 
-	if (sock_net(ue_sk->sk)->user_ns == &init_user_ns) {
-		mutex_lock(&uevent_sock_mutex);
-		list_del(&ue_sk->list);
-		mutex_unlock(&uevent_sock_mutex);
+	scoped_guard(mutex, &uevent_sock_mutex) {
+		ue_sk = net->uevent_sock;
+		net->uevent_sock = NULL;
+		if (ue_sk && sock_net(ue_sk->sk)->user_ns == &init_user_ns)
+			list_del(&ue_sk->list);
 	}
 
+	if (!ue_sk)
+		return;
+
 	netlink_kernel_release(ue_sk->sk);
 	kfree(ue_sk);
 }

Signature · 1 line

2.55.0