vfs: fix lookup on deleted directory

commit d70b67c8bc72ee23b55381bd6a884f4796692f77 upstream

Lookup can install a child dentry for a deleted directory.  This keeps
the directory dentry alive, and the inode pinned in the cache and on
disk, even after all external references have gone away.

This isn't a big problem normally, since memory pressure or umount
will clear out the directory dentry and its children, releasing the
inode.  But for UBIFS this causes problems because its orphan area can
overflow.

Fix this by returning ENOENT for all lookups on a S_DEAD directory
before creating a child dentry.

Thanks to Zoltan Sogor for noticing this while testing UBIFS, and
Artem for the excellent analysis of the problem and testing.

Reported-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Tested-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/namei.c b/fs/namei.c
index a16f1ae6081b46cc6b0cf6146df67b5c2f4f9d0e..a6fdd952274d0bf0c124fe3c36ce08168af90ac9 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -514,7 +514,14 @@ static struct dentry * real_lookup(struct dentry * parent, struct qstr * name, s
         */
        result = d_lookup(parent, name);
        if (!result) {
-               struct dentry * dentry = d_alloc(parent, name);
+               struct dentry *dentry;
+
+               /* Don't create child dentry for a dead directory. */
+               result = ERR_PTR(-ENOENT);
+               if (IS_DEADDIR(dir))
+                       goto out_unlock;
+
+               dentry = d_alloc(parent, name);
                result = ERR_PTR(-ENOMEM);
                if (dentry) {
                        result = dir->i_op->lookup(dir, dentry, nd);
@@ -523,6 +530,7 @@ static struct dentry * real_lookup(struct dentry * parent, struct qstr * name, s
                        else
                                result = dentry;
                }
+out_unlock:
                mutex_unlock(&dir->i_mutex);
                return result;
        }
@@ -1313,7 +1321,14 @@ static struct dentry *__lookup_hash(struct qstr *name,
 
        dentry = cached_lookup(base, name, nd);
        if (!dentry) {
-               struct dentry *new = d_alloc(base, name);
+               struct dentry *new;
+
+               /* Don't create child dentry for a dead directory. */
+               dentry = ERR_PTR(-ENOENT);
+               if (IS_DEADDIR(inode))
+                       goto out;
+
+               new = d_alloc(base, name);
                dentry = ERR_PTR(-ENOMEM);
                if (!new)
                        goto out;