From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753162AbdFMLgA (ORCPT ); Tue, 13 Jun 2017 07:36:00 -0400 Received: from mx2.suse.de ([195.135.220.15]:57089 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752418AbdFMLf6 (ORCPT ); Tue, 13 Jun 2017 07:35:58 -0400 From: Jiri Slaby To: jlayton@redhat.com Cc: linux-kernel@vger.kernel.org, Jiri Slaby , Jeff Layton , "J. Bruce Fields" , Alexander Viro , linux-fsdevel@vger.kernel.org Subject: [PATCH v3 2/2] fs/fcntl: f_setown, avoid undefined behaviour Date: Tue, 13 Jun 2017 13:35:51 +0200 Message-Id: <20170613113551.15098-2-jslaby@suse.cz> X-Mailer: git-send-email 2.13.1 In-Reply-To: <20170613113551.15098-1-jslaby@suse.cz> References: <20170613113551.15098-1-jslaby@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org fcntl(0, F_SETOWN, 0x80000000) triggers: UBSAN: Undefined behaviour in fs/fcntl.c:118:7 negation of -2147483648 cannot be represented in type 'int': CPU: 1 PID: 18261 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1 ... Call Trace: ... [] ? f_setown+0x1d8/0x200 [] ? SyS_fcntl+0x999/0xf30 [] ? entry_SYSCALL_64_fastpath+0x23/0xc1 Fix that by checking the arg parameter properly (against INT_MAX) before "who = -who". And return immediatelly with -EINVAL in case it is wrong. Note that according to POSIX we can return EINVAL: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html [EINVAL] The cmd argument is F_SETOWN and the value of the argument is not valid as a process or process group identifier. [v2] returns an error, v1 used to fail silently [v3] implement proper check for the bad value INT_MIN Signed-off-by: Jiri Slaby Cc: Jeff Layton Cc: "J. Bruce Fields" Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org --- fs/fcntl.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/fcntl.c b/fs/fcntl.c index 313eba860346..693322e28751 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -116,6 +116,10 @@ int f_setown(struct file *filp, unsigned long arg, int force) int who = arg; type = PIDTYPE_PID; if (who < 0) { + /* avoid overflow below */ + if (who == INT_MIN) + return -EINVAL; + type = PIDTYPE_PGID; who = -who; } -- 2.13.1