libfs: Modify mount_pseudo_xattr to be clear it is not a userspace mount

[ Upstream commit 7542272 ] Add MS_KERNMOUNT to the flags that are passed. Use sget_userns and force &init_user_ns instead of calling sget so that even if called from a weird context the internal filesystem will be considered to be in the intial user namespace. Luis Ressel reported that the the failure to pass MS_KERNMOUNT into mount_pseudo broke his in development graphics driver that uses the generic drm infrastructure. I am not certain the deriver was bug free in it's usage of that infrastructure but since mount_pseudo_xattr can never be triggered by userspace it is clearer and less error prone, and less problematic for the code to be explicit. Reported-by: Luis Ressel <[email protected]> Tested-by: Luis Ressel <[email protected]> Acked-by: Al Viro <[email protected]> Signed-off-by: "Eric W. Biederman" <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]>
klaby · Dec 9, 2017 · c4081f9 · c4081f9
1 parent d9a4e70
commit c4081f9
Showing 1 changed file with 2 additions and 1 deletion.
diff --git a/fs/libfs.c b/fs/libfs.c
@@ -245,7 +245,8 @@ struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name,
 	struct inode *root;
 	struct qstr d_name = QSTR_INIT(name, strlen(name));
 
-	s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL);
+	s = sget_userns(fs_type, NULL, set_anon_super, MS_KERNMOUNT|MS_NOUSER,
+			&init_user_ns, NULL);
 	if (IS_ERR(s))
 		return ERR_CAST(s);