* [PATCH net 1/2] vsock: fix child netns mode initialization
2026-02-12 20:59 [PATCH net 0/2] vsock: fix child netns mode initialization and restriction Stefano Garzarella
@ 2026-02-12 20:59 ` Stefano Garzarella
2026-02-13 1:14 ` Bobby Eshleman
2026-02-12 20:59 ` [PATCH net 2/2] vsock: prevent child netns mode switch from local to global Stefano Garzarella
2026-02-13 20:40 ` [PATCH net 0/2] vsock: fix child netns mode initialization and restriction patchwork-bot+netdevbpf
2 siblings, 1 reply; 6+ messages in thread
From: Stefano Garzarella @ 2026-02-12 20:59 UTC (permalink / raw)
To: netdev
Cc: Eric Dumazet, linux-kernel, Bobby Eshleman, Jakub Kicinski,
Stefano Garzarella, virtualization, Paolo Abeni,
Michael S. Tsirkin, Simon Horman, David S. Miller
From: Stefano Garzarella <sgarzare@redhat.com>
When a new network namespace is created, vsock_net_init() correctly
initializes the namespace's mode by reading the parent's `child_ns_mode`
via vsock_net_child_mode(). However, the `child_ns_mode` of the new
namespace was always hardcoded to VSOCK_NET_MODE_GLOBAL, regardless of
its own mode.
This means that if a parent namespace has `child_ns_mode` set to "local",
the child namespace correctly gets mode "local", but its `child_ns_mode`
is reset to "global". As a result, further nested namespaces will
incorrectly get mode "global" instead of inheriting "local", breaking
the expected propagation of the mode through nested namespaces.
Fix this by initializing `child_ns_mode` to the namespace's own mode,
so the setting propagates correctly through all levels of nesting.
Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
Cc: bobbyeshleman@meta.com
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
net/vmw_vsock/af_vsock.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 20ad2b2dc17b..3b629b4a0359 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -91,7 +91,8 @@
* - /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
- * child namespaces will inherit when created. The default is "global".
+ * 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. At namespace creation, ns_mode
@@ -2912,7 +2913,7 @@ static void vsock_net_init(struct net *net)
else
net->vsock.mode = vsock_net_child_mode(current->nsproxy->net_ns);
- net->vsock.child_ns_mode = VSOCK_NET_MODE_GLOBAL;
+ net->vsock.child_ns_mode = net->vsock.mode;
}
static __net_init int vsock_sysctl_init_net(struct net *net)
--
2.53.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH net 1/2] vsock: fix child netns mode initialization
2026-02-12 20:59 ` [PATCH net 1/2] vsock: fix child netns mode initialization Stefano Garzarella
@ 2026-02-13 1:14 ` Bobby Eshleman
0 siblings, 0 replies; 6+ messages in thread
From: Bobby Eshleman @ 2026-02-13 1:14 UTC (permalink / raw)
To: Stefano Garzarella
Cc: netdev, Eric Dumazet, linux-kernel, Bobby Eshleman,
Jakub Kicinski, virtualization, Paolo Abeni, Michael S. Tsirkin,
Simon Horman, David S. Miller
On Thu, Feb 12, 2026 at 09:59:15PM +0100, Stefano Garzarella wrote:
> From: Stefano Garzarella <sgarzare@redhat.com>
>
> When a new network namespace is created, vsock_net_init() correctly
> initializes the namespace's mode by reading the parent's `child_ns_mode`
> via vsock_net_child_mode(). However, the `child_ns_mode` of the new
> namespace was always hardcoded to VSOCK_NET_MODE_GLOBAL, regardless of
> its own mode.
>
> This means that if a parent namespace has `child_ns_mode` set to "local",
> the child namespace correctly gets mode "local", but its `child_ns_mode`
> is reset to "global". As a result, further nested namespaces will
> incorrectly get mode "global" instead of inheriting "local", breaking
> the expected propagation of the mode through nested namespaces.
>
> Fix this by initializing `child_ns_mode` to the namespace's own mode,
> so the setting propagates correctly through all levels of nesting.
>
> Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
> Cc: bobbyeshleman@meta.com
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> net/vmw_vsock/af_vsock.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 20ad2b2dc17b..3b629b4a0359 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -91,7 +91,8 @@
> * - /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
> - * child namespaces will inherit when created. The default is "global".
> + * 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. At namespace creation, ns_mode
> @@ -2912,7 +2913,7 @@ static void vsock_net_init(struct net *net)
> else
> net->vsock.mode = vsock_net_child_mode(current->nsproxy->net_ns);
>
> - net->vsock.child_ns_mode = VSOCK_NET_MODE_GLOBAL;
> + net->vsock.child_ns_mode = net->vsock.mode;
> }
>
> static __net_init int vsock_sysctl_init_net(struct net *net)
> --
> 2.53.0
>
LGTM.
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH net 2/2] vsock: prevent child netns mode switch from local to global
2026-02-12 20:59 [PATCH net 0/2] vsock: fix child netns mode initialization and restriction Stefano Garzarella
2026-02-12 20:59 ` [PATCH net 1/2] vsock: fix child netns mode initialization Stefano Garzarella
@ 2026-02-12 20:59 ` Stefano Garzarella
2026-02-13 1:19 ` Bobby Eshleman
2026-02-13 20:40 ` [PATCH net 0/2] vsock: fix child netns mode initialization and restriction patchwork-bot+netdevbpf
2 siblings, 1 reply; 6+ messages in thread
From: Stefano Garzarella @ 2026-02-12 20:59 UTC (permalink / raw)
To: netdev
Cc: Eric Dumazet, linux-kernel, Bobby Eshleman, Jakub Kicinski,
Stefano Garzarella, virtualization, Paolo Abeni,
Michael S. Tsirkin, Simon Horman, David S. Miller
From: Stefano Garzarella <sgarzare@redhat.com>
A "local" namespace can change its `child_ns_mode` sysctl to "global",
allowing nested namespaces to access global CIDs. This can be exploited
by an unprivileged user who gained CAP_NET_ADMIN through a user
namespace.
Prevent this by rejecting writes that attempt to set `child_ns_mode` to
"global" when the current namespace's mode is "local".
Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
Cc: bobbyeshleman@meta.com
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
net/vmw_vsock/af_vsock.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 3b629b4a0359..9880756d9eff 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -95,8 +95,9 @@
* the namespace's own ns_mode.
*
* Changing child_ns_mode only affects newly created namespaces, not the
- * current namespace or existing children. At namespace creation, ns_mode
- * is inherited from the parent's child_ns_mode.
+ * 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.
*
* The init_net mode is "global" and cannot be modified.
*
@@ -2844,8 +2845,16 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write,
if (ret)
return ret;
- if (write)
+ if (write) {
+ /* Prevent a "local" namespace from escalating to "global",
+ * which would give nested namespaces access to global CIDs.
+ */
+ if (vsock_net_mode(net) == VSOCK_NET_MODE_LOCAL &&
+ new_mode == VSOCK_NET_MODE_GLOBAL)
+ return -EPERM;
+
vsock_net_set_child_mode(net, new_mode);
+ }
return 0;
}
--
2.53.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH net 2/2] vsock: prevent child netns mode switch from local to global
2026-02-12 20:59 ` [PATCH net 2/2] vsock: prevent child netns mode switch from local to global Stefano Garzarella
@ 2026-02-13 1:19 ` Bobby Eshleman
0 siblings, 0 replies; 6+ messages in thread
From: Bobby Eshleman @ 2026-02-13 1:19 UTC (permalink / raw)
To: Stefano Garzarella
Cc: netdev, Eric Dumazet, linux-kernel, Bobby Eshleman,
Jakub Kicinski, virtualization, Paolo Abeni, Michael S. Tsirkin,
Simon Horman, David S. Miller
On Thu, Feb 12, 2026 at 09:59:16PM +0100, Stefano Garzarella wrote:
> From: Stefano Garzarella <sgarzare@redhat.com>
>
> A "local" namespace can change its `child_ns_mode` sysctl to "global",
> allowing nested namespaces to access global CIDs. This can be exploited
> by an unprivileged user who gained CAP_NET_ADMIN through a user
> namespace.
>
> Prevent this by rejecting writes that attempt to set `child_ns_mode` to
> "global" when the current namespace's mode is "local".
>
> Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
> Cc: bobbyeshleman@meta.com
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> net/vmw_vsock/af_vsock.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 3b629b4a0359..9880756d9eff 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -95,8 +95,9 @@
> * the namespace's own ns_mode.
> *
> * Changing child_ns_mode only affects newly created namespaces, not the
> - * current namespace or existing children. At namespace creation, ns_mode
> - * is inherited from the parent's child_ns_mode.
> + * 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.
> *
> * The init_net mode is "global" and cannot be modified.
> *
> @@ -2844,8 +2845,16 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write,
> if (ret)
> return ret;
>
> - if (write)
> + if (write) {
> + /* Prevent a "local" namespace from escalating to "global",
> + * which would give nested namespaces access to global CIDs.
> + */
> + if (vsock_net_mode(net) == VSOCK_NET_MODE_LOCAL &&
> + new_mode == VSOCK_NET_MODE_GLOBAL)
> + return -EPERM;
> +
> vsock_net_set_child_mode(net, new_mode);
> + }
>
> return 0;
> }
> --
> 2.53.0
>
Thanks for the fix!
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH net 0/2] vsock: fix child netns mode initialization and restriction
2026-02-12 20:59 [PATCH net 0/2] vsock: fix child netns mode initialization and restriction Stefano Garzarella
2026-02-12 20:59 ` [PATCH net 1/2] vsock: fix child netns mode initialization Stefano Garzarella
2026-02-12 20:59 ` [PATCH net 2/2] vsock: prevent child netns mode switch from local to global Stefano Garzarella
@ 2026-02-13 20:40 ` patchwork-bot+netdevbpf
2 siblings, 0 replies; 6+ messages in thread
From: patchwork-bot+netdevbpf @ 2026-02-13 20:40 UTC (permalink / raw)
To: Stefano Garzarella
Cc: netdev, edumazet, linux-kernel, bobbyeshleman, kuba,
virtualization, pabeni, mst, horms, davem
Hello:
This series was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:
On Thu, 12 Feb 2026 21:59:14 +0100 you wrote:
> This series fixes two issues in the vsock network namespace support
> recently introduced by commit eafb64f40ca4 ("vsock: add netns to vsock
> core").
>
> Patch 1 fixes `child_ns_mode` being always hardcoded to "global" for new
> namespaces, breaking propagation of the "local" mode through nested
> namespaces.
>
> [...]
Here is the summary with links:
- [net,1/2] vsock: fix child netns mode initialization
https://git.kernel.org/netdev/net/c/9dd391493a72
- [net,2/2] vsock: prevent child netns mode switch from local to global
https://git.kernel.org/netdev/net/c/6a997f38bdf8
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
^ permalink raw reply [flat|nested] 6+ messages in thread