statmount: permission check should return EPERM

Currently, statmount() returns ENOENT when caller is not CAP_SYS_ADMIN
in the user namespace owner of target mount namespace. This should be
EPERM instead.

Suggested-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Bhavik Sachdev <b.sachdev1904@gmail.com>
Link: https://patch.msgid.link/20251129091455.757724-2-b.sachdev1904@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: bsach64

fs/namespace.c

@@ -5780,7 +5780,7 @@ SYSCALL_DEFINE4(statmount, const struct mnt_id_req __user *, req,
 
 	if (kreq.mnt_ns_id && (ns != current->nsproxy->mnt_ns) &&
 	    !ns_capable_noaudit(ns->user_ns, CAP_SYS_ADMIN))
-		return -ENOENT;
+		return -EPERM;
 
 	ks = kmalloc(sizeof(*ks), GFP_KERNEL_ACCOUNT);
 	if (!ks)