On Wed, Apr 01, 2026 at 11:21:53AM +0200, Stefano Garzarella wrote: > From: Stefano Garzarella <[email protected]> > > The `child_ns_mode_locked` field lives in `struct net`, which persists > across vsock module reloads. When the module is unloaded and reloaded, > `vsock_net_init()` resets `mode` and `child_ns_mode` back to their > default values, but does not reset `child_ns_mode_locked`. > > The stale lock from the previous module load causes subsequent writes > to `child_ns_mode` to silently fail: `vsock_net_set_child_mode()` sees > the old lock, skips updating the actual value, and returns success > when the requested mode matches the stale lock. The sysctl handler > reports no error, but `child_ns_mode` remains unchanged. > > Steps to reproduce: > $ modprobe vsock > $ echo local > /proc/sys/net/vsock/child_ns_mode > $ cat /proc/sys/net/vsock/child_ns_mode > local > $ modprobe -r vsock > $ modprobe vsock > $ echo local > /proc/sys/net/vsock/child_ns_mode > $ cat /proc/sys/net/vsock/child_ns_mode > global <--- expected "local" > > Fix this by initializing `child_ns_mode_locked` to 0 (unlocked) in > `vsock_net_init()`, so the write-once mechanism works correctly after > module reload. > > Fixes: 102eab95f025 ("vsock: lock down child_ns_mode as write-once") > Cc: [email protected] > Reported-by: Jin Liu <[email protected]> > Signed-off-by: Stefano Garzarella <[email protected]> > --- > net/vmw_vsock/af_vsock.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c > index 2f7d94d682cb..d912ed2f012a 100644 > --- a/net/vmw_vsock/af_vsock.c > +++ b/net/vmw_vsock/af_vsock.c > @@ -2928,6 +2928,7 @@ static void vsock_net_init(struct net *net) > net->vsock.mode = > vsock_net_child_mode(current->nsproxy->net_ns); > > net->vsock.child_ns_mode = net->vsock.mode; > + net->vsock.child_ns_mode_locked = 0; > } > > static __net_init int vsock_sysctl_init_net(struct net *net) > -- > 2.53.0 >
Reviewed-by: Bobby Eshleman <[email protected]>
