jfs: don't allow os2 xattr namespace overlap with others

It's currently possible to bypass xattr namespace access rules by
prefixing valid xattr names with "os2.", since the os2 namespace stores
extended attributes in a legacy format with no prefix.

This patch adds checking to deny access to any valid namespace prefix
following "os2.".

Signed-off-by: Dave Kleikamp <[e-mail]>
Reported-by: Sergey Vlasov <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/jfs/xattr.c

···
 #define EA_MALLOC	0x0008
 
 
+static int is_known_namespace(const char *name)
+{
+	if (strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN) &&
+	    strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) &&
+	    strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) &&
+	    strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
+		return false;
+
+	return true;
+}
+
 /*
  * These three routines are used to recognize on-disk extended attributes
  * that are in a recognized namespace.  If the attribute is not recognized,
  * "os2." is prepended to the name
  */
-static inline int is_os2_xattr(struct jfs_ea *ea)
+static int is_os2_xattr(struct jfs_ea *ea)
 {
-	/*
-	 * Check for "system."
-	 */
-	if ((ea->namelen >= XATTR_SYSTEM_PREFIX_LEN) &&
-	    !strncmp(ea->name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
-		return false;
-	/*
-	 * Check for "user."
-	 */
-	if ((ea->namelen >= XATTR_USER_PREFIX_LEN) &&
-	    !strncmp(ea->name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
-		return false;
-	/*
-	 * Check for "security."
-	 */
-	if ((ea->namelen >= XATTR_SECURITY_PREFIX_LEN) &&
-	    !strncmp(ea->name, XATTR_SECURITY_PREFIX,
-		     XATTR_SECURITY_PREFIX_LEN))
-		return false;
-	/*
-	 * Check for "trusted."
-	 */
-	if ((ea->namelen >= XATTR_TRUSTED_PREFIX_LEN) &&
-	    !strncmp(ea->name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN))
-		return false;
-	/*
-	 * Add any other valid namespace prefixes here
-	 */
-
-	/*
-	 * We assume it's OS/2's flat namespace
-	 */
-	return true;
+	return !is_known_namespace(ea->name);
 }
 
 static inline int name_size(struct jfs_ea *ea)
···
 	if (!strncmp(name, XATTR_SYSTEM_PREFIX, XATTR_SYSTEM_PREFIX_LEN))
 		return can_set_system_xattr(inode, name, value, value_len);
 
+	if (!strncmp(name, XATTR_OS2_PREFIX, XATTR_OS2_PREFIX_LEN)) {
+		/*
+		 * This makes sure that we aren't trying to set an
+		 * attribute in a different namespace by prefixing it
+		 * with "os2."
+		 */
+		if (is_known_namespace(name + XATTR_OS2_PREFIX_LEN))
+				return -EOPNOTSUPP;
+		return 0;
+	}
+
 	/*
 	 * Don't allow setting an attribute in an unknown namespace.
 	 */
 	if (strncmp(name, XATTR_TRUSTED_PREFIX, XATTR_TRUSTED_PREFIX_LEN) &&
 	    strncmp(name, XATTR_SECURITY_PREFIX, XATTR_SECURITY_PREFIX_LEN) &&
-	    strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN) &&
-	    strncmp(name, XATTR_OS2_PREFIX, XATTR_OS2_PREFIX_LEN))
+	    strncmp(name, XATTR_USER_PREFIX, XATTR_USER_PREFIX_LEN))
 		return -EOPNOTSUPP;
 
 	return 0;
···
 	int xattr_size;
 	ssize_t size;
 	int namelen = strlen(name);
-	char *os2name = NULL;
 	char *value;
-
-	if (strncmp(name, XATTR_OS2_PREFIX, XATTR_OS2_PREFIX_LEN) == 0) {
-		os2name = kmalloc(namelen - XATTR_OS2_PREFIX_LEN + 1,
-				  GFP_KERNEL);
-		if (!os2name)
-			return -ENOMEM;
-		strcpy(os2name, name + XATTR_OS2_PREFIX_LEN);
-		name = os2name;
-		namelen -= XATTR_OS2_PREFIX_LEN;
-	}
 
 	down_read(&JFS_IP(inode)->xattr_sem);
 
···
       out:
 	up_read(&JFS_IP(inode)->xattr_sem);
 
-	kfree(os2name);
-
 	return size;
 }
 
···
 		     size_t buf_size)
 {
 	int err;
+
+	if (strncmp(name, XATTR_OS2_PREFIX, XATTR_OS2_PREFIX_LEN) == 0) {
+		/*
+		 * skip past "os2." prefix
+		 */
+		name += XATTR_OS2_PREFIX_LEN;
+		/*
+		 * Don't allow retrieving properly prefixed attributes
+		 * by prepending them with "os2."
+		 */
+		if (is_known_namespace(name))
+			return -EOPNOTSUPP;
+	}
 
 	err = __jfs_getxattr(dentry->d_inode, name, data, buf_size);