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

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

[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 <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
---
 lib/kobject_uevent.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index ddbc4d7482d2..ecba33abb6b1 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -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);
-- 
2.55.0

Re: [PATCH] kobject: fix uevent socket use-after-free on net namespace delete

[Greg KH]

On Thu, Sep 17, 2026 at 08:12:06PM +0530, Adarsh Das wrote:
> 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 <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
> Link: https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
> Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
> ---
>  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

Re: [PATCH] kobject: fix uevent socket use-after-free on net namespace delete

[Adarsh Das]

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.

Re: [PATCH] kobject: fix uevent socket use-after-free on net namespace delete

[Greg KH]

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

On Thu, Sep 17, 2026 at 08:48:30PM +0530, Adarsh Das wrote:
> Hi,
> 
> Sorry, I wasn't aware of the Assisted-by tag before. Should I send a
> V2 with it?

Please do.

> 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.

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

[PATCH v2] kobject: fix uevent socket use-after-free on net namespace delete

[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

[PATCH v2] kobject: fix uevent socket use-after-free on net namespace delete

[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 <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
Tested-by: syzbot <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
Tested-by: Adarsh Das <adarshdas950@gmail.com>
Assisted-by: Cursor AI
Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
---
 lib/kobject_uevent.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index ddbc4d7482d2..ecba33abb6b1 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -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);
-- 
2.55.0

Re: [PATCH v2] kobject: fix uevent socket use-after-free on net namespace delete

[Greg KH]

On Thu, Sep 17, 2026 at 10:38:26PM +0530, Adarsh Das wrote:
> 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 <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
> Link: https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
> Tested-by: syzbot <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
> Tested-by: Adarsh Das <adarshdas950@gmail.com>
> Assisted-by: Cursor AI
> Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
> ---
>  lib/kobject_uevent.c | 24 +++++++++++++++++-------
>  1 file changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index ddbc4d7482d2..ecba33abb6b1 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -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

[PATCH v3] kobject: fix uevent socket use-after-free on net namespace delete

[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 <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
Link: https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
Tested-by: syzbot <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
Tested-by: Adarsh Das <adarshdas950@gmail.com>
Assisted-by: LLM
Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
---
 lib/kobject_uevent.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index ddbc4d7482d2..cb674c2c3432 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -13,6 +13,7 @@
  *	Greg Kroah-Hartman	<greg@kroah.com>
  */
 
+#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);
 }
-- 
2.55.0

Re: [PATCH v3] kobject: fix uevent socket use-after-free on net namespace delete

[Greg KH]

On Fri, Sep 18, 2026 at 11:38:26AM +0530, Adarsh Das wrote:
> 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 <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
> Link: https://syzkaller.appspot.com/bug?extid=4393dfdddf166f2de2b0
> Tested-by: syzbot <syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com>
> Tested-by: Adarsh Das <adarshdas950@gmail.com>
> Assisted-by: LLM
> Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
> ---
>  lib/kobject_uevent.c | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index ddbc4d7482d2..cb674c2c3432 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -13,6 +13,7 @@
>   *	Greg Kroah-Hartman	<greg@kroah.com>
>   */
>  
> +#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);
>  }
> -- 
> 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.

You are receiving this message because of the following common error(s)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
  did not list below the --- line any changes from the previous version.
  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/process/submitting-patches.rst for what
  needs to be done here to properly describe this.

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,

greg k-h's patch email bot

Re: [PATCH v3] kobject: fix uevent socket use-after-free on net namespace delete

[Greg KH]

On Fri, Sep 18, 2026 at 11:38:26AM +0530, Adarsh Das wrote:
> @@ -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

[PATCH v4] kobject: fix uevent socket use-after-free on net namespace delete

[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.

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: syzbot+4393dfdddf166f2de2b0@syzkaller.appspotmail.com
Tested-by: Adarsh Das <adarshdas950@gmail.com>
Assisted-by: LLM
Link: https://lore.kernel.org/all/20260917144206.85836-1-adarshdas950@gmail.com/
Signed-off-by: Adarsh Das <adarshdas950@gmail.com>
---
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(-)

diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index ddbc4d7482d2..14e2e15d4ea7 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -13,6 +13,7 @@
  *	Greg Kroah-Hartman	<greg@kroah.com>
  */
 
+#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);
 }
-- 
2.55.0