ovl: make ovl_create_real() cope with vfs_mkdir() safely

vfs_mkdir() may succeed and leave the dentry passed to it unhashed and
negative.  ovl_create_real() is the last caller breaking when that
happens.

[amir: split re-factoring of ovl_create_temp() to prep patch
       add comment about unhashed dir after mkdir
       add pr_warn() if mkdir succeeds and lookup fails]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 1b181292a6247771a71e261c445f257180388ca2..1d59c466d199f0adb3bc5eb12c1336ac78210d32 100644 (file)
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -114,6 +114,37 @@ int ovl_cleanup_and_whiteout(struct dentry *workdir, struct inode *dir,
        goto out;
 }
 
+static int ovl_mkdir_real(struct inode *dir, struct dentry **newdentry,
+                         umode_t mode)
+{
+       int err;
+       struct dentry *d, *dentry = *newdentry;
+
+       err = ovl_do_mkdir(dir, dentry, mode);
+       if (err)
+               return err;
+
+       if (likely(!d_unhashed(dentry)))
+               return 0;
+
+       /*
+        * vfs_mkdir() may succeed and leave the dentry passed
+        * to it unhashed and negative. If that happens, try to
+        * lookup a new hashed and positive dentry.
+        */
+       d = lookup_one_len(dentry->d_name.name, dentry->d_parent,
+                          dentry->d_name.len);
+       if (IS_ERR(d)) {
+               pr_warn("overlayfs: failed lookup after mkdir (%pd2, err=%i).\n",
+                       dentry, err);
+               return PTR_ERR(d);
+       }
+       dput(dentry);
+       *newdentry = d;
+
+       return 0;
+}
+
 struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
                               struct ovl_cattr *attr)
 {
@@ -135,7 +166,8 @@ struct dentry *ovl_create_real(struct inode *dir, struct dentry *newdentry,
                        break;
 
                case S_IFDIR:
-                       err = ovl_do_mkdir(dir, newdentry, attr->mode);
+                       /* mkdir is special... */
+                       err =  ovl_mkdir_real(dir, &newdentry, attr->mode);
                        break;
 
                case S_IFCHR: