autofs4 - use simple_empty() for empty directory check

For direct (and offset) mounts, if an automounted mount is manually
umounted the trigger mount dentry can appear non-empty causing it to
not trigger mounts. This can also happen if there is a file handle
leak in a user space automounting application.

This happens because, when a ioctl control file handle is opened
on the mount, a cursor dentry is created which causes list_empty()
to see the dentry as non-empty. Since there is a case where listing
the directory of these dentrys is needed, the use of dcache_dir_*()
functions for .open() and .release() is needed.

Consequently simple_empty() must be used instead of list_empty()
when checking for an empty directory.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 17 deletions

diff --git a/fs/autofs4/root.c b/fs/autofs4/root.c
index 30a6ab66e99a..c93447604da8 100644
--- a/fs/autofs4/root.c
+++ b/fs/autofs4/root.c
@@ -124,13 +124,10 @@ static int autofs4_dir_open(struct inode *inode, struct file *file)
          * it.
          */
         spin_lock(&sbi->lookup_lock);
-        spin_lock(&dentry->d_lock);
-        if (!d_mountpoint(dentry) && list_empty(&dentry->d_subdirs)) {
-                spin_unlock(&dentry->d_lock);
+        if (!d_mountpoint(dentry) && simple_empty(dentry)) {
                 spin_unlock(&sbi->lookup_lock);
                 return -ENOENT;
         }
-        spin_unlock(&dentry->d_lock);
         spin_unlock(&sbi->lookup_lock);
 
 out:
@@ -386,12 +383,8 @@ static struct vfsmount *autofs4_d_automount(struct path *path)
                                 goto done;
                         }
                 } else {
-                        spin_lock(&dentry->d_lock);
-                        if (!list_empty(&dentry->d_subdirs)) {
-                                spin_unlock(&dentry->d_lock);
+                        if (!simple_empty(dentry))
                                 goto done;
-                        }
-                        spin_unlock(&dentry->d_lock);
                 }
                 ino->flags |= AUTOFS_INF_PENDING;
                 spin_unlock(&sbi->fs_lock);
@@ -610,9 +603,7 @@ static int autofs4_dir_unlink(struct inode *dir, struct dentry *dentry)
 
         spin_lock(&sbi->lookup_lock);
         __autofs4_add_expiring(dentry);
-        spin_lock(&dentry->d_lock);
-        __d_drop(dentry);
-        spin_unlock(&dentry->d_lock);
+        d_drop(dentry);
         spin_unlock(&sbi->lookup_lock);
 
         return 0;
@@ -683,15 +674,12 @@ static int autofs4_dir_rmdir(struct inode *dir, struct dentry *dentry)
                 return -EACCES;
 
         spin_lock(&sbi->lookup_lock);
-        spin_lock(&dentry->d_lock);
-        if (!list_empty(&dentry->d_subdirs)) {
-                spin_unlock(&dentry->d_lock);
+        if (!simple_empty(dentry)) {
                 spin_unlock(&sbi->lookup_lock);
                 return -ENOTEMPTY;
         }
         __autofs4_add_expiring(dentry);
-        __d_drop(dentry);
-        spin_unlock(&dentry->d_lock);
+        d_drop(dentry);
         spin_unlock(&sbi->lookup_lock);
 
         if (sbi->version < 5)