Don't pass inode to ->d_hash() and ->d_compare()

Instances either don't look at it at all (the majority of cases) or
only want it to find the superblock (which can be had as dentry->d_sb).
A few cases that want more are actually safe with dentry->d_inode -
the only precaution needed is the check that it hadn't been replaced with
NULL by rmdir() or by overwriting rename(), which case should be simply
treated as cache miss.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 24 insertions, 8 deletions

diff --git a/fs/ncpfs/dir.c b/fs/ncpfs/dir.c
index 3bc105d36f10..3be047474bfc 100644
--- a/fs/ncpfs/dir.c
+++ b/fs/ncpfs/dir.c
@@ -73,10 +73,8 @@ const struct inode_operations ncp_dir_inode_operations =
  * Dentry operations routines
  */
 static int ncp_lookup_validate(struct dentry *, unsigned int);
-static int ncp_hash_dentry(const struct dentry *, const struct inode *,
-                struct qstr *);
-static int ncp_compare_dentry(const struct dentry *, const struct inode *,
-                const struct dentry *, const struct inode *,
+static int ncp_hash_dentry(const struct dentry *, struct qstr *);
+static int ncp_compare_dentry(const struct dentry *, const struct dentry *,
                 unsigned int, const char *, const struct qstr *);
 static int ncp_delete_dentry(const struct dentry *);
 
@@ -119,11 +117,19 @@ static inline int ncp_case_sensitive(const struct inode *i)
 /*
  * Note: leave the hash unchanged if the directory
  * is case-sensitive.
+ *
+ * Accessing the parent inode can be racy under RCU pathwalking.
+ * Use ACCESS_ONCE() to make sure we use _one_ particular inode,
+ * the callers will handle races.
  */
 static int 
-ncp_hash_dentry(const struct dentry *dentry, const struct inode *inode,
-                struct qstr *this)
+ncp_hash_dentry(const struct dentry *dentry, struct qstr *this)
 {
+        struct inode *inode = ACCESS_ONCE(dentry->d_inode);
+
+        if (!inode)
+                return 0;
+
         if (!ncp_case_sensitive(inode)) {
                 struct super_block *sb = dentry->d_sb;
                 struct nls_table *t;
@@ -140,14 +146,24 @@ ncp_hash_dentry(const struct dentry *dentry, const struct inode *inode,
         return 0;
 }
 
+/*
+ * Accessing the parent inode can be racy under RCU pathwalking.
+ * Use ACCESS_ONCE() to make sure we use _one_ particular inode,
+ * the callers will handle races.
+ */
 static int
-ncp_compare_dentry(const struct dentry *parent, const struct inode *pinode,
-                const struct dentry *dentry, const struct inode *inode,
+ncp_compare_dentry(const struct dentry *parent, const struct dentry *dentry,
                 unsigned int len, const char *str, const struct qstr *name)
 {
+        struct inode *pinode;
+
         if (len != name->len)
                 return 1;
 
+        pinode = ACCESS_ONCE(parent->d_inode);
+        if (!pinode)
+                return 1;
+
         if (ncp_case_sensitive(pinode))
                 return strncmp(str, name->name, len);