[PATCH 20/21] Unionfs: Added several BUG_ONs to assert dentry validity

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

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

This should help catch races between the VFS and the branch-management code.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Signed-off-by: Josef 'Jeff' Sipek <jsipek@cs.sunysb.edu>
---
 fs/unionfs/inode.c  |   15 +++++++++++++++
 fs/unionfs/rename.c |    3 +++
 fs/unionfs/super.c  |    2 ++
 fs/unionfs/union.h  |   13 +++++++++++++
 fs/unionfs/unlink.c |    4 ++++
 fs/unionfs/xattr.c  |    8 ++++++++
 6 files changed, 45 insertions(+), 0 deletions(-)

diff --git a/fs/unionfs/inode.c b/fs/unionfs/inode.c
index 5c452b6..97dad8c 100644
--- a/fs/unionfs/inode.c
+++ b/fs/unionfs/inode.c
@@ -249,6 +249,9 @@ static int unionfs_link(struct dentry *old_dentry, struct inode *dir,
 	struct dentry *whiteout_dentry;
 	char *name = NULL;
 
+	BUG_ON(!is_valid_dentry(new_dentry));
+	BUG_ON(!is_valid_dentry(old_dentry));
+
 	double_lock_dentry(new_dentry, old_dentry);
 
 	hidden_new_dentry = unionfs_lower_dentry(new_dentry);
@@ -373,6 +376,8 @@ static int unionfs_symlink(struct inode *dir, struct dentry *dentry,
 	int bindex = 0, bstart;
 	char *name = NULL;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 
 	/* We start out in the leftmost branch. */
@@ -495,6 +500,8 @@ static int unionfs_mkdir(struct inode *parent, struct dentry *dentry, int mode)
 	int whiteout_unlinked = 0;
 	struct sioq_args args;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 	bstart = dbstart(dentry);
 
@@ -622,6 +629,8 @@ static int unionfs_mknod(struct inode *dir, struct dentry *dentry, int mode,
 	char *name = NULL;
 	int whiteout_unlinked = 0;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 	bstart = dbstart(dentry);
 
@@ -724,6 +733,8 @@ static int unionfs_readlink(struct dentry *dentry, char __user * buf,
 	int err;
 	struct dentry *hidden_dentry;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 	hidden_dentry = unionfs_lower_dentry(dentry);
 
@@ -749,6 +760,8 @@ static void *unionfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 	int len = PAGE_SIZE, err;
 	mm_segment_t old_fs;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	/* This is freed by the put_link method assuming a successful call. */
 	buf = kmalloc(len, GFP_KERNEL);
 	if (!buf) {
@@ -908,6 +921,8 @@ static int unionfs_setattr(struct dentry *dentry, struct iattr *ia)
 	int i;
 	int copyup = 0;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 	bstart = dbstart(dentry);
 	bend = dbend(dentry);
diff --git a/fs/unionfs/rename.c b/fs/unionfs/rename.c
index c9aa040..0044492 100644
--- a/fs/unionfs/rename.c
+++ b/fs/unionfs/rename.c
@@ -379,6 +379,9 @@ int unionfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	int err = 0;
 	struct dentry *wh_dentry;
 
+	BUG_ON(!is_valid_dentry(old_dentry));
+	BUG_ON(!is_valid_dentry(new_dentry));
+
 	double_lock_dentry(old_dentry, new_dentry);
 
 	if (!S_ISDIR(old_dentry->d_inode->i_mode))
diff --git a/fs/unionfs/super.c b/fs/unionfs/super.c
index 5d11908..ec5706b 100644
--- a/fs/unionfs/super.c
+++ b/fs/unionfs/super.c
@@ -129,6 +129,8 @@ static int unionfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	int err	= 0;
 	struct super_block *sb, *hidden_sb;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	sb = dentry->d_sb;
 
 	unionfs_read_lock(sb);
diff --git a/fs/unionfs/union.h b/fs/unionfs/union.h
index faaa87e..b6fa0a2 100644
--- a/fs/unionfs/union.h
+++ b/fs/unionfs/union.h
@@ -399,6 +399,19 @@ static inline int is_robranch(const struct dentry *dentry)
 	return is_robranch_idx(dentry, index);
 }
 
+/*
+ * Check if dentry is valid or not, as per our generation numbers.
+ * @dentry: dentry to check.
+ * Returns 1 (valid) or 0 (invalid/stale).
+ */
+static inline int is_valid_dentry(struct dentry *dentry)
+{
+	BUG_ON(!UNIONFS_D(dentry));
+	BUG_ON(!UNIONFS_SB(dentry->d_sb));
+	return (atomic_read(&UNIONFS_D(dentry)->generation) ==
+		atomic_read(&UNIONFS_SB(dentry->d_sb)->generation));
+}
+
 /* What do we use for whiteouts. */
 #define UNIONFS_WHPFX ".wh."
 #define UNIONFS_WHLEN 4
diff --git a/fs/unionfs/unlink.c b/fs/unionfs/unlink.c
index f5b250a..dd1dd9c 100644
--- a/fs/unionfs/unlink.c
+++ b/fs/unionfs/unlink.c
@@ -74,6 +74,8 @@ int unionfs_unlink(struct inode *dir, struct dentry *dentry)
 {
 	int err = 0;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 
 	err = unionfs_unlink_whiteout(dir, dentry);
@@ -122,6 +124,8 @@ int unionfs_rmdir(struct inode *dir, struct dentry *dentry)
 	int err = 0;
 	struct unionfs_dir_state *namelist = NULL;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 
 	/* check if this unionfs directory is empty or not */
diff --git a/fs/unionfs/xattr.c b/fs/unionfs/xattr.c
index d57f079..6e1f4bd 100644
--- a/fs/unionfs/xattr.c
+++ b/fs/unionfs/xattr.c
@@ -56,6 +56,8 @@ ssize_t unionfs_getxattr(struct dentry * dentry, const char *name, void *value,
 	struct dentry *hidden_dentry = NULL;
 	int err = -EOPNOTSUPP;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 
 	hidden_dentry = unionfs_lower_dentry(dentry);
@@ -75,6 +77,8 @@ int unionfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 	struct dentry *hidden_dentry = NULL;
 	int err = -EOPNOTSUPP;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 	hidden_dentry = unionfs_lower_dentry(dentry);
 
@@ -92,6 +96,8 @@ int unionfs_removexattr(struct dentry *dentry, const char *name)
 	struct dentry *hidden_dentry = NULL;
 	int err = -EOPNOTSUPP;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 	hidden_dentry = unionfs_lower_dentry(dentry);
 
@@ -110,6 +116,8 @@ ssize_t unionfs_listxattr(struct dentry * dentry, char *list, size_t size)
 	int err = -EOPNOTSUPP;
 	char *encoded_list = NULL;
 
+	BUG_ON(!is_valid_dentry(dentry));
+
 	unionfs_lock_dentry(dentry);
 
 	hidden_dentry = unionfs_lower_dentry(dentry);
-- 
1.5.0.3.268.g3dda