autofs: use path_is_mountpoint() to fix unreliable d_mountpoint() checks

If an automount mount is clone(2)ed into a file system that is propagation
private, when it later expires in the originating namespace, subsequent
calls to autofs ->d_automount() for that dentry in the original namespace
will return ELOOP until the mount is umounted in the cloned namespace.

Now that a struct path is available where needed use path_is_mountpoint()
instead of d_mountpoint() so we don't get false positives when checking if
a dentry is a mount point in the current namespace.

Link: http://lkml.kernel.org/r/20161011053418.27645.15241.stgit@pluto.themaw.net
Signed-off-by: Ian Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 0e9881552881f756f9a053acd313251aa5e1ba7b..9355608cb49519664ef11228ef1a85c2b8c421df 100644 (file)
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -123,7 +123,7 @@ static int autofs4_dir_open(struct inode *inode, struct file *file)
         * it.
         */
        spin_lock(&sbi->lookup_lock);
-       if (!d_mountpoint(dentry) && simple_empty(dentry)) {
+       if (!path_is_mountpoint(&file->f_path) && simple_empty(dentry)) {
                spin_unlock(&sbi->lookup_lock);
                return -ENOENT;
        }
@@ -372,15 +372,15 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
 
        /*
         * If the dentry is a symlink it's equivalent to a directory
-        * having d_mountpoint() true, so there's no need to call back
-        * to the daemon.
+        * having path_is_mountpoint() true, so there's no need to call
+        * back to the daemon.
         */
        if (d_really_is_positive(dentry) && d_is_symlink(dentry)) {
                spin_unlock(&sbi->fs_lock);
                goto done;
        }
 
-       if (!d_mountpoint(dentry)) {
+       if (!path_is_mountpoint(path)) {
                /*
                 * It's possible that user space hasn't removed directories
                 * after umounting a rootless multi-mount, although it
@@ -434,7 +434,7 @@ static int autofs4_d_manage(const struct path *path, bool rcu_walk)
 
        /* The daemon never waits. */
        if (autofs4_oz_mode(sbi)) {
-               if (!d_mountpoint(dentry))
+               if (!path_is_mountpoint(path))
                        return -EISDIR;
                return 0;
        }
@@ -463,7 +463,7 @@ static int autofs4_d_manage(const struct path *path, bool rcu_walk)
 
                if (ino->flags & AUTOFS_INF_WANT_EXPIRE)
                        return 0;
-               if (d_mountpoint(dentry))
+               if (path_is_mountpoint(path))
                        return 0;
                inode = d_inode_rcu(dentry);
                if (inode && S_ISLNK(inode->i_mode))
@@ -490,7 +490,7 @@ static int autofs4_d_manage(const struct path *path, bool rcu_walk)
                 * we can avoid needless calls ->d_automount() and avoid
                 * an incorrect ELOOP error return.
                 */
-               if ((!d_mountpoint(dentry) && !simple_empty(dentry)) ||
+               if ((!path_is_mountpoint(path) && !simple_empty(dentry)) ||
                    (d_really_is_positive(dentry) && d_is_symlink(dentry)))
                        status = -EISDIR;
        }