Return-Path: Received: from mx3-rdu2.redhat.com ([66.187.233.73]:42834 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752805AbeDQULT (ORCPT ); Tue, 17 Apr 2018 16:11:19 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 22F4E4023BAD for ; Tue, 17 Apr 2018 20:11:19 +0000 (UTC) Received: from f27-node1.dwysocha.net (dhcp145-42.rdu.redhat.com [10.13.145.42]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 199437C37 for ; Tue, 17 Apr 2018 20:11:19 +0000 (UTC) From: Dave Wysochanski To: linux-nfs@vger.kernel.org Subject: [PATCH] Fix possible stack smash in nfs_idmap_read_and_verify_message Date: Tue, 17 Apr 2018 16:11:18 -0400 Message-Id: <20180417201118.17841-1-dwysocha@redhat.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: In nfs_idmap_read_and_verify_message there is an unprotected sprintf that converts the __u32 'im_id' from struct idmap_msg to 'id_str' that is a stack variable of 'NFS_UINT_MAXLEN' (defined as 11). If a uid or gid value is > 2147483647 = 0x7fffffff we corrupt kernel memory by one byte and if CONFIG_CC_STACKPROTECTOR_STRONG is set we see a stack-protector panic as follows: [11558053.616565] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: ffffffffa05b8a8c [11558053.639063] CPU: 6 PID: 9423 Comm: rpc.idmapd Tainted: G W ------------ T 3.10.0-514.el7.x86_64 #1 [11558053.641990] Hardware name: Red Hat OpenStack Compute, BIOS 1.10.2-3.el7_4.1 04/01/2014 [11558053.644462] ffffffff818c7bc0 00000000b1f3aec1 ffff880de0f9bd48 ffffffff81685eac [11558053.646430] ffff880de0f9bdc8 ffffffff8167f2b3 ffffffff00000010 ffff880de0f9bdd8 [11558053.648313] ffff880de0f9bd78 00000000b1f3aec1 ffffffff811dcb03 ffffffffa05b8a8c [11558053.650107] Call Trace: [11558053.651347] [] dump_stack+0x19/0x1b [11558053.653013] [] panic+0xe3/0x1f2 [11558053.666240] [] ? kfree+0x103/0x140 [11558053.682589] [] ? idmap_pipe_downcall+0x1cc/0x1e0 [nfsv4] [11558053.689710] [] __stack_chk_fail+0x1b/0x30 [11558053.691619] [] idmap_pipe_downcall+0x1cc/0x1e0 [nfsv4] [11558053.693867] [] rpc_pipe_write+0x56/0x70 [sunrpc] [11558053.695763] [] vfs_write+0xbd/0x1e0 [11558053.702236] [] ? task_work_run+0xac/0xe0 [11558053.704215] [] SyS_write+0x7f/0xe0 [11558053.709674] [] system_call_fastpath+0x16/0x1b Fix this by snprintf and a safe length based on sizeof(id_str). Signed-off-by: Dave Wysochanski Reported-by: Stephen Johnston --- fs/nfs/nfs4idmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/nfs/nfs4idmap.c b/fs/nfs/nfs4idmap.c index 22dc30a679a0..a8c663f8dd99 100644 --- a/fs/nfs/nfs4idmap.c +++ b/fs/nfs/nfs4idmap.c @@ -627,7 +627,7 @@ static int nfs_idmap_read_and_verify_message(struct idmap_msg *im, if (strcmp(upcall->im_name, im->im_name) != 0) break; /* Note: here we store the NUL terminator too */ - len = sprintf(id_str, "%d", im->im_id) + 1; + len = snprintf(id_str, sizeof(id_str), "%u", im->im_id) + 1; ret = nfs_idmap_instantiate(key, authkey, id_str, len); break; case IDMAP_CONV_IDTONAME: -- 2.14.3