fix race in audit_get_nd()

don't rely on pathname resolution ending up twice at the same point...

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

1 files changed, 32 insertions, 53 deletions

diff --git a/kernel/audit_watch.c b/kernel/audit_watch.c
index d2e3c7866460..20b9fe6907d0 100644
--- a/kernel/audit_watch.c
+++ b/kernel/audit_watch.c
@@ -144,9 +144,9 @@ int audit_watch_compare(struct audit_watch *watch, unsigned long ino, dev_t dev)
 }
 
 /* Initialize a parent watch entry. */
-static struct audit_parent *audit_init_parent(struct nameidata *ndp)
+static struct audit_parent *audit_init_parent(struct path *path)
 {
-        struct inode *inode = ndp->path.dentry->d_inode;
+        struct inode *inode = path->dentry->d_inode;
         struct audit_parent *parent;
         int ret;
 
@@ -353,53 +353,40 @@ static void audit_remove_parent_watches(struct audit_parent *parent)
 }
 
 /* Get path information necessary for adding watches. */
-static int audit_get_nd(char *path, struct nameidata **ndp, struct nameidata **ndw)
+static int audit_get_nd(struct audit_watch *watch, struct path *parent)
 {
-        struct nameidata *ndparent, *ndwatch;
+        struct nameidata nd;
+        struct dentry *d;
         int err;
 
-        ndparent = kmalloc(sizeof(*ndparent), GFP_KERNEL);
-        if (unlikely(!ndparent))
-                return -ENOMEM;
+        err = path_lookup(watch->path, LOOKUP_PARENT, &nd);
+        if (err)
+                return err;
 
-        ndwatch = kmalloc(sizeof(*ndwatch), GFP_KERNEL);
-        if (unlikely(!ndwatch)) {
-                kfree(ndparent);
-                return -ENOMEM;
+        if (nd.last_type != LAST_NORM) {
+                path_put(&nd.path);
+                return -EINVAL;
         }
 
-        err = path_lookup(path, LOOKUP_PARENT, ndparent);
-        if (err) {
-                kfree(ndparent);
-                kfree(ndwatch);
-                return err;
+        mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
+        d = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
+        if (IS_ERR(d)) {
+                mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
+                path_put(&nd.path);
+                return PTR_ERR(d);
         }
-
-        err = path_lookup(path, 0, ndwatch);
-        if (err) {
-                kfree(ndwatch);
-                ndwatch = NULL;
+        if (d->d_inode) {
+                /* update watch filter fields */
+                watch->dev = d->d_inode->i_sb->s_dev;
+                watch->ino = d->d_inode->i_ino;
         }
+        mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 
-        *ndp = ndparent;
-        *ndw = ndwatch;
-
+        *parent = nd.path;
+        dput(d);
         return 0;
 }
 
-/* Release resources used for watch path information. */
-static void audit_put_nd(struct nameidata *ndp, struct nameidata *ndw)
-{
-        if (ndp) {
-                path_put(&ndp->path);
-                kfree(ndp);
-        }
-        if (ndw) {
-                path_put(&ndw->path);
-                kfree(ndw);
-        }
-}
-
 /* Associate the given rule with an existing parent.
  * Caller must hold audit_filter_mutex. */
 static void audit_add_to_parent(struct audit_krule *krule,
@@ -440,31 +427,24 @@ int audit_add_watch(struct audit_krule *krule, struct list_head **list)
 {
         struct audit_watch *watch = krule->watch;
         struct audit_parent *parent;
-        struct nameidata *ndp = NULL, *ndw = NULL;
+        struct path parent_path;
         int h, ret = 0;
 
         mutex_unlock(&audit_filter_mutex);
 
         /* Avoid calling path_lookup under audit_filter_mutex. */
-        ret = audit_get_nd(watch->path, &ndp, &ndw);
-        if (ret) {
-                /* caller expects mutex locked */
-                mutex_lock(&audit_filter_mutex);
-                goto error;
-        }
+        ret = audit_get_nd(watch, &parent_path);
 
+        /* caller expects mutex locked */
         mutex_lock(&audit_filter_mutex);
 
-        /* update watch filter fields */
-        if (ndw) {
-                watch->dev = ndw->path.dentry->d_inode->i_sb->s_dev;
-                watch->ino = ndw->path.dentry->d_inode->i_ino;
-        }
+        if (ret)
+                return ret;
 
         /* either find an old parent or attach a new one */
-        parent = audit_find_parent(ndp->path.dentry->d_inode);
+        parent = audit_find_parent(parent_path.dentry->d_inode);
         if (!parent) {
-                parent = audit_init_parent(ndp);
+                parent = audit_init_parent(&parent_path);
                 if (IS_ERR(parent)) {
                         ret = PTR_ERR(parent);
                         goto error;
@@ -479,9 +459,8 @@ int audit_add_watch(struct audit_krule *krule, struct list_head **list)
         h = audit_hash_ino((u32)watch->ino);
         *list = &audit_inode_hash[h];
 error:
-        audit_put_nd(ndp, ndw);         /* NULL args OK */
+        path_put(&parent_path);
         return ret;
-
 }
 
 void audit_remove_watch_rule(struct audit_krule *krule)