[PATCH 25/32] Unionfs: readonly branch test fix

["Josef 'Jeff' Sipek" <jsipek@cs.sunysb.edu>]

From: Erez Zadok <ezk@cs.sunysb.edu>

Bug fix to test if a lower branch is readonly, even when given negative
dentries.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Josef 'Jeff' Sipek <jsipek@cs.sunysb.edu>
---
 fs/unionfs/union.h |   19 ++++++++++++++-----
 1 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/fs/unionfs/union.h b/fs/unionfs/union.h
index 33c2137..26d886e 100644
--- a/fs/unionfs/union.h
+++ b/fs/unionfs/union.h
@@ -396,14 +396,23 @@ static inline int is_robranch_super(const struct super_block *sb, int index)
 /* Is this file on a read-only branch? */
 static inline int is_robranch_idx(const struct dentry *dentry, int index)
 {
-	int err = 0;
+	struct super_block *lower_sb;
 
 	BUG_ON(index < 0);
 
-	if ((!(branchperms(dentry->d_sb, index) & MAY_WRITE)) ||
-	    IS_RDONLY(unionfs_lower_dentry_idx(dentry, index)->d_inode))
-		err = -EROFS;
-	return err;
+	if (!(branchperms(dentry->d_sb, index) & MAY_WRITE))
+		return -EROFS;
+
+	lower_sb = unionfs_lower_super_idx(dentry->d_sb, index);
+	BUG_ON(lower_sb == NULL);
+	/*
+	 * test sb flags directly, not IS_RDONLY(lower_inode) because the
+	 * lower_dentry could be a negative.
+	 */
+	if (lower_sb->s_flags & MS_RDONLY)
+		return -EROFS;
+
+	return 0;
 }
 
 static inline int is_robranch(const struct dentry *dentry)
-- 
1.5.2.2.238.g7cbf2f2