mount: consolidate permission checks

... and ask for global CAP_SYS_ADMIN only for superblock-level remounts

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 7 insertions, 33 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index edac42c6eff2..269919fa116d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1300,24 +1300,6 @@ SYSCALL_DEFINE1(oldumount, char __user *, name)
 
 #endif
 
-static int mount_is_safe(struct path *path)
-{
-        if (may_mount())
-                return 0;
-        return -EPERM;
-#ifdef notyet
-        if (S_ISLNK(path->dentry->d_inode->i_mode))
-                return -EPERM;
-        if (path->dentry->d_inode->i_mode & S_ISVTX) {
-                if (current_uid() != path->dentry->d_inode->i_uid)
-                        return -EPERM;
-        }
-        if (inode_permission(path->dentry->d_inode, MAY_WRITE))
-                return -EPERM;
-        return 0;
-#endif
-}
-
 static bool mnt_ns_loop(struct path *path)
 {
         /* Could bind mounting the mount namespace inode cause a
@@ -1640,9 +1622,6 @@ static int do_change_type(struct path *path, int flag)
         int type;
         int err = 0;
 
-        if (!may_mount())
-                return -EPERM;
-
         if (path->dentry != path->mnt->mnt_root)
                 return -EINVAL;
 
@@ -1676,9 +1655,7 @@ static int do_loopback(struct path *path, const char *old_name,
         LIST_HEAD(umount_list);
         struct path old_path;
         struct mount *mnt = NULL, *old;
-        int err = mount_is_safe(path);
-        if (err)
-                return err;
+        int err;
         if (!old_name || !*old_name)
                 return -EINVAL;
         err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
@@ -1755,9 +1732,6 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
         struct super_block *sb = path->mnt->mnt_sb;
         struct mount *mnt = real_mount(path->mnt);
 
-        if (!capable(CAP_SYS_ADMIN))
-                return -EPERM;
-
         if (!check_mnt(mnt))
                 return -EINVAL;
 
@@ -1771,6 +1745,8 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
         down_write(&sb->s_umount);
         if (flags & MS_BIND)
                 err = change_mount_flags(path->mnt, flags);
+        else if (!capable(CAP_SYS_ADMIN))
+                err = -EPERM;
         else
                 err = do_remount_sb(sb, flags, data, 0);
         if (!err) {
@@ -1803,9 +1779,7 @@ static int do_move_mount(struct path *path, const char *old_name)
         struct path old_path, parent_path;
         struct mount *p;
         struct mount *old;
-        int err = 0;
-        if (!may_mount())
-                return -EPERM;
+        int err;
         if (!old_name || !*old_name)
                 return -EINVAL;
         err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
@@ -1947,9 +1921,6 @@ static int do_new_mount(struct path *path, const char *fstype, int flags,
         if (!fstype)
                 return -EINVAL;
 
-        if (!may_mount())
-                return -EPERM;
-
         type = get_fs_type(fstype);
         if (!type)
                 return -ENODEV;
@@ -2263,6 +2234,9 @@ long do_mount(const char *dev_name, const char *dir_name,
         if (retval)
                 goto dput_out;
 
+        if (!may_mount())
+                return -EPERM;
+
         /* Default to relatime unless overriden */
         if (!(flags & MS_NOATIME))
                 mnt_flags |= MNT_RELATIME;