btrfs: don't accept bare namespace as a valid xattr

Due to insufficient check in btrfs_is_valid_xattr, this unexpectedly
works:

 $ touch file
 $ setfattr -n user. -v 1 file
 $ getfattr -d file
user.="1"

ie. the missing attribute name after the namespace.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=94291
Reported-by: William Douglas <william.douglas@intel.com>
CC: <stable@vger.kernel.org> # 2.6.29+
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 39 insertions, 14 deletions

diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
index 883b93623bc5..45ea704be030 100644
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -364,22 +364,42 @@ const struct xattr_handler *btrfs_xattr_handlers[] = {
 /*
  * Check if the attribute is in a supported namespace.
  *
- * This applied after the check for the synthetic attributes in the system
+ * This is applied after the check for the synthetic attributes in the system
  * namespace.
  */
-static bool btrfs_is_valid_xattr(const char *name)
+static int btrfs_is_valid_xattr(const char *name)
 {
-        return !strncmp(name, XATTR_SECURITY_PREFIX,
-                        XATTR_SECURITY_PREFIX_LEN) ||
-               !strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN) ||
-               !strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) ||
-               !strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) ||
-                !strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN);
+        int len = strlen(name);
+        int prefixlen = 0;
+
+        if (!strncmp(name, XATTR_SECURITY_PREFIX,
+                        XATTR_SECURITY_PREFIX_LEN))
+                prefixlen = XATTR_SECURITY_PREFIX_LEN;
+        else if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
+                prefixlen = XATTR_SYSTEM_PREFIX_LEN;
+        else if (!strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
+                prefixlen = XATTR_TRUSTED_PREFIX_LEN;
+        else if (!strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
+                prefixlen = XATTR_USER_PREFIX_LEN;
+        else if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
+                prefixlen = XATTR_BTRFS_PREFIX_LEN;
+        else
+                return -EOPNOTSUPP;
+
+        /*
+         * The name cannot consist of just prefix
+         */
+        if (len <= prefixlen)
+                return -EINVAL;
+
+        return 0;
 }
 
 ssize_t btrfs_getxattr(struct dentry *dentry, const char *name,
                        void *buffer, size_t size)
 {
+        int ret;
+
         /*
          * If this is a request for a synthetic attribute in the system.*
          * namespace use the generic infrastructure to resolve a handler
@@ -388,8 +408,9 @@ ssize_t btrfs_getxattr(struct dentry *dentry, const char *name,
         if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
                 return generic_getxattr(dentry, name, buffer, size);
 
-        if (!btrfs_is_valid_xattr(name))
-                return -EOPNOTSUPP;
+        ret = btrfs_is_valid_xattr(name);
+        if (ret)
+                return ret;
         return __btrfs_getxattr(dentry->d_inode, name, buffer, size);
 }
 
@@ -397,6 +418,7 @@ int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
                    size_t size, int flags)
 {
         struct btrfs_root *root = BTRFS_I(dentry->d_inode)->root;
+        int ret;
 
         /*
          * The permission on security.* and system.* is not checked
@@ -413,8 +435,9 @@ int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
         if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
                 return generic_setxattr(dentry, name, value, size, flags);
 
-        if (!btrfs_is_valid_xattr(name))
-                return -EOPNOTSUPP;
+        ret = btrfs_is_valid_xattr(name);
+        if (ret)
+                return ret;
 
         if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
                 return btrfs_set_prop(dentry->d_inode, name,
@@ -430,6 +453,7 @@ int btrfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 int btrfs_removexattr(struct dentry *dentry, const char *name)
 {
         struct btrfs_root *root = BTRFS_I(dentry->d_inode)->root;
+        int ret;
 
         /*
          * The permission on security.* and system.* is not checked
@@ -446,8 +470,9 @@ int btrfs_removexattr(struct dentry *dentry, const char *name)
         if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
                 return generic_removexattr(dentry, name);
 
-        if (!btrfs_is_valid_xattr(name))
-                return -EOPNOTSUPP;
+        ret = btrfs_is_valid_xattr(name);
+        if (ret)
+                return ret;
 
         if (!strncmp(name, XATTR_BTRFS_PREFIX, XATTR_BTRFS_PREFIX_LEN))
                 return btrfs_set_prop(dentry->d_inode, name,