ima: use file_dentry()

BugLink: http://bugs.launchpad.net/bugs/1634153

commit e71b9dff upstream.

Ima tries to call ->setxattr() on overlayfs dentry after having locked
underlying inode, which results in a deadlock.
Reported-by: Krisztian Litkey <kli@iki.fi>
Fixes: 4bacc9c9 ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>

security/integrity/ima/ima_api.c

@@ -202,7 +202,7 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
 	} hash;
 
 	if (xattr_value)
-		*xattr_len = ima_read_xattr(file->f_path.dentry, xattr_value);
+		*xattr_len = ima_read_xattr(file_dentry(file), xattr_value);
 
 	if (!(iint->flags & IMA_COLLECTED)) {
 		u64 i_version = file_inode(file)->i_version;

security/integrity/ima/ima_appraise.c

@@ -189,7 +189,7 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 {
 	static const char op[] = "appraise_data";
 	char *cause = "unknown";
-	struct dentry *dentry = file->f_path.dentry;
+	struct dentry *dentry = file_dentry(file);
 	struct inode *inode = d_backing_inode(dentry);
 	enum integrity_status status = INTEGRITY_UNKNOWN;
 	int rc = xattr_len, hash_start = 0;
@@ -289,7 +289,7 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
  */
 void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
 {
-	struct dentry *dentry = file->f_path.dentry;
+	struct dentry *dentry = file_dentry(file);
 	int rc = 0;
 
 	/* do not collect and update hash for digital signatures */