hostfs: fix races in dentry_name() and inode_name()

calculating size, then doing allocation, then filling the
path is a Bad Idea(tm), since the ancestors can be renamed,
leading to buffer overrun.

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

1 files changed, 60 insertions, 46 deletions

diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 10bb71b1548b..79783a0b2f4d 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -90,44 +90,58 @@ __uml_setup("hostfs=", hostfs_args,
 );
 #endif
 
-static char *dentry_name(struct dentry *dentry)
+static char *__dentry_name(struct dentry *dentry, char *name)
 {
-        struct dentry *parent;
-        char *root, *name;
-        int len;
+        char *p = __dentry_path(dentry, name, PATH_MAX);
+        char *root;
+        size_t len;
 
-        len = 0;
-        parent = dentry;
-        while (parent->d_parent != parent) {
-                len += parent->d_name.len + 1;
-                parent = parent->d_parent;
-        }
+        spin_unlock(&dcache_lock);
 
-        root = parent->d_sb->s_fs_info;
-        len += strlen(root);
-        name = kmalloc(len + 1, GFP_KERNEL);
-        if (name == NULL)
+        root = dentry->d_sb->s_fs_info;
+        len = strlen(root);
+        if (IS_ERR(p)) {
+                __putname(name);
                 return NULL;
-
-        name[len] = '\0';
-        parent = dentry;
-        while (parent->d_parent != parent) {
-                len -= parent->d_name.len + 1;
-                name[len] = '/';
-                strncpy(&name[len + 1], parent->d_name.name,
-                        parent->d_name.len);
-                parent = parent->d_parent;
         }
-        strncpy(name, root, strlen(root));
+        strncpy(name, root, PATH_MAX);
+        if (len > p - name) {
+                __putname(name);
+                return NULL;
+        }
+        if (p > name + len) {
+                char *s = name + len;
+                while ((*s++ = *p++) != '\0')
+                        ;
+        }
         return name;
 }
 
+static char *dentry_name(struct dentry *dentry)
+{
+        char *name = __getname();
+        if (!name)
+                return NULL;
+
+        spin_lock(&dcache_lock);
+        return __dentry_name(dentry, name); /* will unlock */
+}
+
 static char *inode_name(struct inode *ino)
 {
         struct dentry *dentry;
+        char *name = __getname();
+        if (!name)
+                return NULL;
 
-        dentry = list_entry(ino->i_dentry.next, struct dentry, d_alias);
-        return dentry_name(dentry);
+        spin_lock(&dcache_lock);
+        if (list_empty(&ino->i_dentry)) {
+                spin_unlock(&dcache_lock);
+                __putname(name);
+                return NULL;
+        }
+        dentry = list_first_entry(&ino->i_dentry, struct dentry, d_alias);
+        return __dentry_name(dentry, name); /* will unlock */
 }
 
 static char *follow_link(char *link)
@@ -272,7 +286,7 @@ int hostfs_readdir(struct file *file, void *ent, filldir_t filldir)
         if (name == NULL)
                 return -ENOMEM;
         dir = open_dir(name, &error);
-        kfree(name);
+        __putname(name);
         if (dir == NULL)
                 return -error;
         next = file->f_pos;
@@ -318,7 +332,7 @@ int hostfs_file_open(struct inode *ino, struct file *file)
                 return -ENOMEM;
 
         fd = open_file(name, r, w, append);
-        kfree(name);
+        __putname(name);
         if (fd < 0)
                 return fd;
         FILE_HOSTFS_I(file)->fd = fd;
@@ -532,7 +546,7 @@ int hostfs_create(struct inode *dir, struct dentry *dentry, int mode,
         else
                 error = read_name(inode, name);
 
-        kfree(name);
+        __putname(name);
         if (error)
                 goto out_put;
 
@@ -567,7 +581,7 @@ struct dentry *hostfs_lookup(struct inode *ino, struct dentry *dentry,
 
         err = read_name(inode, name);
 
-        kfree(name);
+        __putname(name);
         if (err == -ENOENT) {
                 iput(inode);
                 inode = NULL;
@@ -594,12 +608,12 @@ int hostfs_link(struct dentry *to, struct inode *ino, struct dentry *from)
                 return -ENOMEM;
         to_name = dentry_name(to);
         if (to_name == NULL) {
-                kfree(from_name);
+                __putname(from_name);
                 return -ENOMEM;
         }
         err = link_file(to_name, from_name);
-        kfree(from_name);
-        kfree(to_name);
+        __putname(from_name);
+        __putname(to_name);
         return err;
 }
 
@@ -614,7 +628,7 @@ int hostfs_unlink(struct inode *ino, struct dentry *dentry)
                 return -EPERM;
 
         err = unlink_file(file);
-        kfree(file);
+        __putname(file);
         return err;
 }
 
@@ -626,7 +640,7 @@ int hostfs_symlink(struct inode *ino, struct dentry *dentry, const char *to)
         if ((file = dentry_name(dentry)) == NULL)
                 return -ENOMEM;
         err = make_symlink(file, to);
-        kfree(file);
+        __putname(file);
         return err;
 }
 
@@ -638,7 +652,7 @@ int hostfs_mkdir(struct inode *ino, struct dentry *dentry, int mode)
         if ((file = dentry_name(dentry)) == NULL)
                 return -ENOMEM;
         err = do_mkdir(file, mode);
-        kfree(file);
+        __putname(file);
         return err;
 }
 
@@ -650,7 +664,7 @@ int hostfs_rmdir(struct inode *ino, struct dentry *dentry)
         if ((file = dentry_name(dentry)) == NULL)
                 return -ENOMEM;
         err = do_rmdir(file);
-        kfree(file);
+        __putname(file);
         return err;
 }
 
@@ -673,13 +687,13 @@ int hostfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
 
         init_special_inode(inode, mode, dev);
         err = do_mknod(name, mode, MAJOR(dev), MINOR(dev));
-        if (err)
+        if (!err)
                 goto out_free;
 
         err = read_name(inode, name);
+        __putname(name);
         if (err)
                 goto out_put;
-        kfree(name);
         if (err)
                 goto out_put;
 
@@ -687,7 +701,7 @@ int hostfs_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
         return 0;
 
  out_free:
-        kfree(name);
+        __putname(name);
  out_put:
         iput(inode);
  out:
@@ -703,12 +717,12 @@ int hostfs_rename(struct inode *from_ino, struct dentry *from,
         if ((from_name = dentry_name(from)) == NULL)
                 return -ENOMEM;
         if ((to_name = dentry_name(to)) == NULL) {
-                kfree(from_name);
+                __putname(from_name);
                 return -ENOMEM;
         }
         err = rename_file(from_name, to_name);
-        kfree(from_name);
-        kfree(to_name);
+        __putname(from_name);
+        __putname(to_name);
         return err;
 }
 
@@ -729,7 +743,7 @@ int hostfs_permission(struct inode *ino, int desired)
                 err = 0;
         else
                 err = access_file(name, r, w, x);
-        kfree(name);
+        __putname(name);
         if (!err)
                 err = generic_permission(ino, desired, NULL);
         return err;
@@ -790,7 +804,7 @@ int hostfs_setattr(struct dentry *dentry, struct iattr *attr)
         if (name == NULL)
                 return -ENOMEM;
         err = set_attr(name, &attrs, fd);
-        kfree(name);
+        __putname(name);
         if (err)
                 return err;
 
@@ -845,7 +859,7 @@ static void *hostfs_follow_link(struct dentry *dentry, struct nameidata *nd)
                         int err = hostfs_do_readlink(path, link, PATH_MAX);
                         if (err == PATH_MAX)
                                 err = -E2BIG;
-                        kfree(path);
+                        __putname(path);
                 }
                 if (err < 0) {
                         __putname(link);