[PATCH net v3 0/3] vsock: add write-once semantics to child_ns_mode

[PATCH net v3 0/3] vsock: add write-once semantics to child_ns_mode

[Bobby Eshleman]

Two administrator processes may race when setting child_ns_mode: one
sets it to "local" and creates a namespace, but another changes it to
"global" in between. The first process ends up with a namespace in the
wrong mode. Make child_ns_mode write-once so that a namespace manager
can set it once, check the value, and be guaranteed it won't change
before creating its namespaces. Writing a different value after the
first write returns -EBUSY.

One patch for the implementation, one for docs, and one for tests.

---
Changes in v3:
- Simplify code be reverting approach of using only a single variable to
  represent both lock state and child_ns_mode state. Instead, use
  child_ns_mode and child_ns_mode_locked.
- Update documentation to clarify the value-dependent behavior of
  child_ns_mode writes (that is, same value is ok, different value gets
  -EBUSY).
- fixed some line length > 80 checkpatch issues in vmtest.sh
- Link to v2: https://lore.kernel.org/r/20260218-vsock-ns-write-once-v2-0-19e4c50d509a@meta.com

Changes in v2:
- break docs, tests, and implementation into separate patches
- clarify commit message
- only use child_ns_mode, do not add additional child_ns_mode_locked
  variable
- add documentation to Documentation/
- Link to v1: https://lore.kernel.org/r/20260217-vsock-ns-write-once-v1-1-a1fb30f289a9@meta.com

---
Bobby Eshleman (3):
      selftests/vsock: change tests to respect write-once child ns mode
      vsock: lock down child_ns_mode as write-once
      vsock: document write-once behavior of the child_ns_mode sysctl

 Documentation/admin-guide/sysctl/net.rst |  3 +++
 include/net/af_vsock.h                   | 13 ++++++++--
 include/net/netns/vsock.h                |  3 +++
 net/vmw_vsock/af_vsock.c                 | 15 ++++++++----
 tools/testing/selftests/vsock/vmtest.sh  | 41 ++++++++++++++++----------------
 5 files changed, 48 insertions(+), 27 deletions(-)
---
base-commit: ccd8e87748ad083047d6c8544c5809b7f96cc8df
change-id: 20260217-vsock-ns-write-once-8834d684e0a2

Best regards,
-- 
Bobby Eshleman <bobbyeshleman@meta.com>

[PATCH net v3 1/3] selftests/vsock: change tests to respect write-once child ns mode

[Bobby Eshleman]

From: Bobby Eshleman <bobbyeshleman@meta.com>

The child_ns_mode sysctl parameter becomes write-once in a future patch
in this series, which breaks existing tests. This patch updates the
tests to respect this new policy. No additional tests are added.

Add "global-parent" and "local-parent" namespaces as intermediaries to
spawn namespaces in the given modes. This avoids the need to change
"child_ns_mode" in the init_ns. nsenter must be used because ip netns
unshares the mount namespace so nested "ip netns add" breaks exec calls
from the init ns. Adds nsenter to the deps check.

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
 tools/testing/selftests/vsock/vmtest.sh | 41 +++++++++++++++++----------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/tools/testing/selftests/vsock/vmtest.sh b/tools/testing/selftests/vsock/vmtest.sh
index dc8dbe74a6d0..86e338886b33 100755
--- a/tools/testing/selftests/vsock/vmtest.sh
+++ b/tools/testing/selftests/vsock/vmtest.sh
@@ -210,16 +210,21 @@ check_result() {
 }
 
 add_namespaces() {
-	local orig_mode
-	orig_mode=$(cat /proc/sys/net/vsock/child_ns_mode)
-
-	for mode in "${NS_MODES[@]}"; do
-		echo "${mode}" > /proc/sys/net/vsock/child_ns_mode
-		ip netns add "${mode}0" 2>/dev/null
-		ip netns add "${mode}1" 2>/dev/null
-	done
-
-	echo "${orig_mode}" > /proc/sys/net/vsock/child_ns_mode
+	ip netns add "global-parent" 2>/dev/null
+	echo "global" | ip netns exec "global-parent" \
+		tee /proc/sys/net/vsock/child_ns_mode &>/dev/null
+	ip netns add "local-parent" 2>/dev/null
+	echo "local" | ip netns exec "local-parent" \
+		tee /proc/sys/net/vsock/child_ns_mode &>/dev/null
+
+	nsenter --net=/var/run/netns/global-parent \
+		ip netns add "global0" 2>/dev/null
+	nsenter --net=/var/run/netns/global-parent \
+		ip netns add "global1" 2>/dev/null
+	nsenter --net=/var/run/netns/local-parent \
+		ip netns add "local0" 2>/dev/null
+	nsenter --net=/var/run/netns/local-parent \
+		ip netns add "local1" 2>/dev/null
 }
 
 init_namespaces() {
@@ -237,6 +242,8 @@ del_namespaces() {
 		log_host "removed ns ${mode}0"
 		log_host "removed ns ${mode}1"
 	done
+	ip netns del "global-parent" &>/dev/null
+	ip netns del "local-parent" &>/dev/null
 }
 
 vm_ssh() {
@@ -287,7 +294,7 @@ check_args() {
 }
 
 check_deps() {
-	for dep in vng ${QEMU} busybox pkill ssh ss socat; do
+	for dep in vng ${QEMU} busybox pkill ssh ss socat nsenter; do
 		if [[ ! -x $(command -v "${dep}") ]]; then
 			echo -e "skip:    dependency ${dep} not found!\n"
 			exit "${KSFT_SKIP}"
@@ -1231,12 +1238,8 @@ test_ns_local_same_cid_ok() {
 }
 
 test_ns_host_vsock_child_ns_mode_ok() {
-	local orig_mode
-	local rc
-
-	orig_mode=$(cat /proc/sys/net/vsock/child_ns_mode)
+	local rc="${KSFT_PASS}"
 
-	rc="${KSFT_PASS}"
 	for mode in "${NS_MODES[@]}"; do
 		local ns="${mode}0"
 
@@ -1246,15 +1249,13 @@ test_ns_host_vsock_child_ns_mode_ok() {
 			continue
 		fi
 
-		if ! echo "${mode}" > /proc/sys/net/vsock/child_ns_mode; then
-			log_host "child_ns_mode should be writable to ${mode}"
+		if ! echo "${mode}" | ip netns exec "${ns}" \
+			tee /proc/sys/net/vsock/child_ns_mode &>/dev/null; then
 			rc="${KSFT_FAIL}"
 			continue
 		fi
 	done
 
-	echo "${orig_mode}" > /proc/sys/net/vsock/child_ns_mode
-
 	return "${rc}"
 }
 

-- 
2.47.3

[PATCH net v3 2/3] vsock: lock down child_ns_mode as write-once

[Bobby Eshleman]

From: Bobby Eshleman <bobbyeshleman@meta.com>

Two administrator processes may race when setting child_ns_mode as one
process sets child_ns_mode to "local" and then creates a namespace, but
another process changes child_ns_mode to "global" between the write and
the namespace creation. The first process ends up with a namespace in
"global" mode instead of "local". While this can be detected after the
fact by reading ns_mode and retrying, it is fragile and error-prone.

Make child_ns_mode write-once so that a namespace manager can set it
once and be sure it won't change. Writing a different value after the
first write returns -EBUSY. This applies to all namespaces, including
init_net, where an init process can write "local" to lock all future
namespaces into local mode.

Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
Suggested-by: Daan De Meyer <daan.j.demeyer@gmail.com>
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Co-developed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
 include/net/af_vsock.h    | 13 +++++++++++--
 include/net/netns/vsock.h |  3 +++
 net/vmw_vsock/af_vsock.c  | 15 ++++++++++-----
 3 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index d3ff48a2fbe0..533d8e75f7bb 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -276,10 +276,19 @@ static inline bool vsock_net_mode_global(struct vsock_sock *vsk)
 	return vsock_net_mode(sock_net(sk_vsock(vsk))) == VSOCK_NET_MODE_GLOBAL;
 }
 
-static inline void vsock_net_set_child_mode(struct net *net,
+static inline bool vsock_net_set_child_mode(struct net *net,
 					    enum vsock_net_mode mode)
 {
-	WRITE_ONCE(net->vsock.child_ns_mode, mode);
+	int new_locked = mode + 1;
+	int old_locked = 0; /* unlocked */
+
+	if (try_cmpxchg(&net->vsock.child_ns_mode_locked,
+			&old_locked, new_locked)) {
+		WRITE_ONCE(net->vsock.child_ns_mode, mode);
+		return true;
+	}
+
+	return old_locked == new_locked;
 }
 
 static inline enum vsock_net_mode vsock_net_child_mode(struct net *net)
diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h
index b34d69a22fa8..dc8cbe45f406 100644
--- a/include/net/netns/vsock.h
+++ b/include/net/netns/vsock.h
@@ -17,5 +17,8 @@ struct netns_vsock {
 
 	enum vsock_net_mode mode;
 	enum vsock_net_mode child_ns_mode;
+
+	/* 0 = unlocked, 1 = locked to global, 2 = locked to local */
+	int child_ns_mode_locked;
 };
 #endif /* __NET_NET_NAMESPACE_VSOCK_H */
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 9880756d9eff..50044a838c89 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -90,16 +90,20 @@
  *
  *   - /proc/sys/net/vsock/ns_mode (read-only) reports the current namespace's
  *     mode, which is set at namespace creation and immutable thereafter.
- *   - /proc/sys/net/vsock/child_ns_mode (writable) controls what mode future
+ *   - /proc/sys/net/vsock/child_ns_mode (write-once) controls what mode future
  *     child namespaces will inherit when created. The initial value matches
  *     the namespace's own ns_mode.
  *
  *   Changing child_ns_mode only affects newly created namespaces, not the
  *   current namespace or existing children. A "local" namespace cannot set
- *   child_ns_mode to "global". At namespace creation, ns_mode is inherited
- *   from the parent's child_ns_mode.
+ *   child_ns_mode to "global". child_ns_mode is write-once, so that it may be
+ *   configured and locked down by a namespace manager. Writing a different
+ *   value after the first write returns -EBUSY. At namespace creation, ns_mode
+ *   is inherited from the parent's child_ns_mode.
  *
- *   The init_net mode is "global" and cannot be modified.
+ *   The init_net mode is "global" and cannot be modified. The init_net
+ *   child_ns_mode is also write-once, so an init process (e.g. systemd) can
+ *   set it to "local" to ensure all new namespaces inherit local mode.
  *
  *   The modes affect the allocation and accessibility of CIDs as follows:
  *
@@ -2853,7 +2857,8 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write,
 		    new_mode == VSOCK_NET_MODE_GLOBAL)
 			return -EPERM;
 
-		vsock_net_set_child_mode(net, new_mode);
+		if (!vsock_net_set_child_mode(net, new_mode))
+			return -EBUSY;
 	}
 
 	return 0;

-- 
2.47.3

[PATCH net v3 3/3] vsock: document write-once behavior of the child_ns_mode sysctl

[Bobby Eshleman]

From: Bobby Eshleman <bobbyeshleman@meta.com>

Update the vsock child_ns_mode documentation to include the new
write-once semantics of setting child_ns_mode. The semantics are
implemented in a preceding patch in this series.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
Changes in v3:
- update language to clarify language that first value is locked, but subsequent
  writes succeed.
---
 Documentation/admin-guide/sysctl/net.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
index c10530624f1e..3b2ad61995d4 100644
--- a/Documentation/admin-guide/sysctl/net.rst
+++ b/Documentation/admin-guide/sysctl/net.rst
@@ -594,6 +594,9 @@ Values:
 	  their sockets will only be able to connect within their own
 	  namespace.
 
+The first write to ``child_ns_mode`` locks its value. Subsequent writes of the
+same value succeed, but writing a different value returns ``-EBUSY``.
+
 Changing ``child_ns_mode`` only affects namespaces created after the change;
 it does not modify the current namespace or any existing children.
 

-- 
2.47.3

Re: [PATCH net v3 2/3] vsock: lock down child_ns_mode as write-once

[Bobby Eshleman]

On Mon, Feb 23, 2026 at 02:38:33PM -0800, Bobby Eshleman wrote:
> From: Bobby Eshleman <bobbyeshleman@meta.com>
> 
> Two administrator processes may race when setting child_ns_mode as one
> process sets child_ns_mode to "local" and then creates a namespace, but
> another process changes child_ns_mode to "global" between the write and
> the namespace creation. The first process ends up with a namespace in
> "global" mode instead of "local". While this can be detected after the
> fact by reading ns_mode and retrying, it is fragile and error-prone.
> 
> Make child_ns_mode write-once so that a namespace manager can set it
> once and be sure it won't change. Writing a different value after the
> first write returns -EBUSY. This applies to all namespaces, including
> init_net, where an init process can write "local" to lock all future
> namespaces into local mode.
> 
> Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
> Suggested-by: Daan De Meyer <daan.j.demeyer@gmail.com>
> Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
> Co-developed-by: Stefano Garzarella <sgarzare@redhat.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Stefano, I wasn't sure if you wanted the Co-developed-by and S-o-b on
this iteration, but I added it just in case. Please let me know, if that
wasn't what you intended.

Best,
Bobby

Re: [PATCH net v3 2/3] vsock: lock down child_ns_mode as write-once

[Stefano Garzarella]

On Mon, Feb 23, 2026 at 02:38:33PM -0800, Bobby Eshleman wrote:
>From: Bobby Eshleman <bobbyeshleman@meta.com>
>
>Two administrator processes may race when setting child_ns_mode as one
>process sets child_ns_mode to "local" and then creates a namespace, but
>another process changes child_ns_mode to "global" between the write and
>the namespace creation. The first process ends up with a namespace in
>"global" mode instead of "local". While this can be detected after the
>fact by reading ns_mode and retrying, it is fragile and error-prone.
>
>Make child_ns_mode write-once so that a namespace manager can set it
>once and be sure it won't change. Writing a different value after the
>first write returns -EBUSY. This applies to all namespaces, including
>init_net, where an init process can write "local" to lock all future
>namespaces into local mode.
>
>Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
>Suggested-by: Daan De Meyer <daan.j.demeyer@gmail.com>
>Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
>Co-developed-by: Stefano Garzarella <sgarzare@redhat.com>
>Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
>---
> include/net/af_vsock.h    | 13 +++++++++++--
> include/net/netns/vsock.h |  3 +++
> net/vmw_vsock/af_vsock.c  | 15 ++++++++++-----
> 3 files changed, 24 insertions(+), 7 deletions(-)

I still slightly prefer the version I proposed here: 
https://lore.kernel.org/netdev/aZbR2H2oDyIAxDef@sgarzare-redhat/

But this definitely affects the code less, so for `net` I think this 
patch is better:

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

Eventually, we can discuss in net-next patch whether to change the 
implementation to the other one, but for the user nothing changes at 
all.

Thanks,
Stefano

>
>diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
>index d3ff48a2fbe0..533d8e75f7bb 100644
>--- a/include/net/af_vsock.h
>+++ b/include/net/af_vsock.h
>@@ -276,10 +276,19 @@ static inline bool vsock_net_mode_global(struct vsock_sock *vsk)
> 	return vsock_net_mode(sock_net(sk_vsock(vsk))) == VSOCK_NET_MODE_GLOBAL;
> }
>
>-static inline void vsock_net_set_child_mode(struct net *net,
>+static inline bool vsock_net_set_child_mode(struct net *net,
> 					    enum vsock_net_mode mode)
> {
>-	WRITE_ONCE(net->vsock.child_ns_mode, mode);
>+	int new_locked = mode + 1;
>+	int old_locked = 0; /* unlocked */
>+
>+	if (try_cmpxchg(&net->vsock.child_ns_mode_locked,
>+			&old_locked, new_locked)) {
>+		WRITE_ONCE(net->vsock.child_ns_mode, mode);
>+		return true;
>+	}
>+
>+	return old_locked == new_locked;
> }
>
> static inline enum vsock_net_mode vsock_net_child_mode(struct net *net)
>diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h
>index b34d69a22fa8..dc8cbe45f406 100644
>--- a/include/net/netns/vsock.h
>+++ b/include/net/netns/vsock.h
>@@ -17,5 +17,8 @@ struct netns_vsock {
>
> 	enum vsock_net_mode mode;
> 	enum vsock_net_mode child_ns_mode;
>+
>+	/* 0 = unlocked, 1 = locked to global, 2 = locked to local */
>+	int child_ns_mode_locked;
> };
> #endif /* __NET_NET_NAMESPACE_VSOCK_H */
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index 9880756d9eff..50044a838c89 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -90,16 +90,20 @@
>  *
>  *   - /proc/sys/net/vsock/ns_mode (read-only) reports the current namespace's
>  *     mode, which is set at namespace creation and immutable thereafter.
>- *   - /proc/sys/net/vsock/child_ns_mode (writable) controls what mode future
>+ *   - /proc/sys/net/vsock/child_ns_mode (write-once) controls what mode future
>  *     child namespaces will inherit when created. The initial value matches
>  *     the namespace's own ns_mode.
>  *
>  *   Changing child_ns_mode only affects newly created namespaces, not the
>  *   current namespace or existing children. A "local" namespace cannot set
>- *   child_ns_mode to "global". At namespace creation, ns_mode is inherited
>- *   from the parent's child_ns_mode.
>+ *   child_ns_mode to "global". child_ns_mode is write-once, so that it may be
>+ *   configured and locked down by a namespace manager. Writing a different
>+ *   value after the first write returns -EBUSY. At namespace creation, ns_mode
>+ *   is inherited from the parent's child_ns_mode.
>  *
>- *   The init_net mode is "global" and cannot be modified.
>+ *   The init_net mode is "global" and cannot be modified. The init_net
>+ *   child_ns_mode is also write-once, so an init process (e.g. systemd) can
>+ *   set it to "local" to ensure all new namespaces inherit local mode.
>  *
>  *   The modes affect the allocation and accessibility of CIDs as follows:
>  *
>@@ -2853,7 +2857,8 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write,
> 		    new_mode == VSOCK_NET_MODE_GLOBAL)
> 			return -EPERM;
>
>-		vsock_net_set_child_mode(net, new_mode);
>+		if (!vsock_net_set_child_mode(net, new_mode))
>+			return -EBUSY;
> 	}
>
> 	return 0;
>
>-- 
>2.47.3
>

Re: [PATCH net v3 2/3] vsock: lock down child_ns_mode as write-once

[Stefano Garzarella]

On Mon, Feb 23, 2026 at 04:24:07PM -0800, Bobby Eshleman wrote:
>On Mon, Feb 23, 2026 at 02:38:33PM -0800, Bobby Eshleman wrote:
>> From: Bobby Eshleman <bobbyeshleman@meta.com>
>>
>> Two administrator processes may race when setting child_ns_mode as one
>> process sets child_ns_mode to "local" and then creates a namespace, but
>> another process changes child_ns_mode to "global" between the write and
>> the namespace creation. The first process ends up with a namespace in
>> "global" mode instead of "local". While this can be detected after the
>> fact by reading ns_mode and retrying, it is fragile and error-prone.
>>
>> Make child_ns_mode write-once so that a namespace manager can set it
>> once and be sure it won't change. Writing a different value after the
>> first write returns -EBUSY. This applies to all namespaces, including
>> init_net, where an init process can write "local" to lock all future
>> namespaces into local mode.
>>
>> Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
>> Suggested-by: Daan De Meyer <daan.j.demeyer@gmail.com>
>> Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
>> Co-developed-by: Stefano Garzarella <sgarzare@redhat.com>
>> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>
>Stefano, I wasn't sure if you wanted the Co-developed-by and S-o-b on
>this iteration, but I added it just in case. Please let me know, if that
>wasn't what you intended.

It's fine, thanks for that!

Stefano

Re: [PATCH net v3 3/3] vsock: document write-once behavior of the child_ns_mode sysctl

[Stefano Garzarella]

On Mon, Feb 23, 2026 at 02:38:34PM -0800, Bobby Eshleman wrote:
>From: Bobby Eshleman <bobbyeshleman@meta.com>
>
>Update the vsock child_ns_mode documentation to include the new
>write-once semantics of setting child_ns_mode. The semantics are
>implemented in a preceding patch in this series.
>
>Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
>---
>Changes in v3:
>- update language to clarify language that first value is locked, but subsequent
>  writes succeed.
>---
> Documentation/admin-guide/sysctl/net.rst | 3 +++
> 1 file changed, 3 insertions(+)

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

>
>diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst
>index c10530624f1e..3b2ad61995d4 100644
>--- a/Documentation/admin-guide/sysctl/net.rst
>+++ b/Documentation/admin-guide/sysctl/net.rst
>@@ -594,6 +594,9 @@ Values:
> 	  their sockets will only be able to connect within their own
> 	  namespace.
>
>+The first write to ``child_ns_mode`` locks its value. Subsequent writes of the
>+same value succeed, but writing a different value returns ``-EBUSY``.
>+
> Changing ``child_ns_mode`` only affects namespaces created after the change;
> it does not modify the current namespace or any existing children.
>
>
>-- 
>2.47.3
>

Re: [PATCH net v3 0/3] vsock: add write-once semantics to child_ns_mode

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Mon, 23 Feb 2026 14:38:31 -0800 you wrote:
> Two administrator processes may race when setting child_ns_mode: one
> sets it to "local" and creates a namespace, but another changes it to
> "global" in between. The first process ends up with a namespace in the
> wrong mode. Make child_ns_mode write-once so that a namespace manager
> can set it once, check the value, and be guaranteed it won't change
> before creating its namespaces. Writing a different value after the
> first write returns -EBUSY.
> 
> [...]

Here is the summary with links:
  - [net,v3,1/3] selftests/vsock: change tests to respect write-once child ns mode
    https://git.kernel.org/netdev/net/c/a382a34276cb
  - [net,v3,2/3] vsock: lock down child_ns_mode as write-once
    https://git.kernel.org/netdev/net/c/102eab95f025
  - [net,v3,3/3] vsock: document write-once behavior of the child_ns_mode sysctl
    https://git.kernel.org/netdev/net/c/b6302e057fdc

You are awesome, thank you!
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