Re: [PATCH v3] vsock: ignore empty child namespace mode writes

[Stefano Garzarella <sgarzare@redhat.com>]

On Tue, Sep 15, 2026 at 02:30:50PM -0300, Aldo Ariel Panzardo wrote:
>__vsock_net_mode_string() returns success without updating new_mode when
>the transfer length is zero. Its caller then reads the uninitialized enum
>and may permanently store a stack-derived value in the write-once child
>mode.
>
>Return before calling __vsock_net_mode_string() when *lenp is zero so
>that the helper is never invoked with nothing to parse and new_mode is
>never read uninitialized. This also prevents an empty write from
>locking the current mode.
>
>Fixes: eafb64f40ca4 ("vsock: add netns to vsock core")
>Cc: stable@vger.kernel.org
>Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
>Signed-off-by: Aldo Ariel Panzardo <qwe.aldo@gmail.com>
>---
>
>Changes in v3:
>  - Move the !*lenp early return before __vsock_net_mode_string()
>    instead of after it, as suggested by Stefano Garzarella.
>  - Add missing maintainer CCs per get_maintainer.pl.
>  - Add Luigi's Reviewed-by.
>
>Changes in v2:
>  - Return early instead of initializing new_mode to the current
>    value, which would silently consume the write-once transition.
>
> net/vmw_vsock/af_vsock.c | 3 +++
> 1 file changed, 3 insertions(+)
>
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index 622dbd0467..XXXXXXX 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -2879,6 +2879,9 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write,
>
> 	net = container_of(table->data, struct net, vsock.child_ns_mode);
>
>+	if (!*lenp)
>+		return 0;
>+

I would have moved it even before the net assignmet, but in any case, it 
doesn't make much difference:

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