Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751502AbaD0Uvf (ORCPT ); Sun, 27 Apr 2014 16:51:35 -0400 Received: from linuxhacker.ru ([217.76.32.60]:49527 "EHLO fiona.linuxhacker.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751303AbaD0Uve (ORCPT ); Sun, 27 Apr 2014 16:51:34 -0400 From: Oleg Drokin To: linux-kernel@vger.kernel.org Cc: Oleg Drokin , Rohit Seth Subject: [PATCH] sysctl: Fix division by zero in percpu_pagelist_fraction handler Date: Sun, 27 Apr 2014 16:51:07 -0400 Message-Id: <1398631867-6211-1-git-send-email-green@linuxhacker.ru> X-Mailer: git-send-email 1.9.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org percpu_pagelist_fraction_sysctl_handler calls proc_dointvec_minmax and blindly assumes that return value of 0 means success. In fact the other valid case is when it got a zero length input. After that it proceeds to a division by percpu_pagelist_fraction value which is conveniently set to a default of zero, resulting in division by zero. Other than checking the bytecount to be more than zero, perhaps a better default value for percpu_pagelist_fraction would help too. [ 661.985469] divide error: 0000 [#1] SMP DEBUG_PAGEALLOC [ 661.985868] Modules linked in: binfmt_misc cfg80211 rfkill rpcsec_gss_krb5 ttm drm_kms_helper drm i2c_piix4 microcode i2c_core joydev serio_raw pcspkr virtio_blk nfsd [ 661.986008] CPU: 1 PID: 9142 Comm: badarea_io Not tainted 3.15.0-rc2-vm-nfs+ #19 [ 661.986008] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 661.986008] task: ffff8800d5aeb6e0 ti: ffff8800d87a2000 task.ti: ffff8800d87a2000 [ 661.986008] RIP: 0010:[] [] percpu_pagelist_fraction_sysctl_handler+0x84/0x120 [ 661.988031] RSP: 0018:ffff8800d87a3e78 EFLAGS: 00010246 [ 661.988031] RAX: 0000000000000f89 RBX: ffff88011f7fd000 RCX: 0000000000000000 [ 661.988031] RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000010 [ 661.988031] RBP: ffff8800d87a3e98 R08: ffffffff81d002c8 R09: ffff8800d87a3f50 [ 661.988031] R10: 000000000000000b R11: 0000000000000246 R12: 0000000000000060 [ 661.988031] R13: ffffffff81c3c3e0 R14: ffffffff81cfddf8 R15: ffff8801193b0800 [ 661.988031] FS: 00007f614f1e9740(0000) GS:ffff88011f440000(0000) knlGS:0000000000000000 [ 661.988031] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 661.988031] CR2: 00007f614f1fa000 CR3: 00000000d9291000 CR4: 00000000000006e0 [ 661.988031] Stack: [ 661.988031] 0000000000000001 ffffffffffffffea ffffffff81c3c3e0 0000000000000000 [ 661.988031] ffff8800d87a3ee8 ffffffff8122b163 ffff8800d87a3f50 00007fff1564969c [ 661.988031] 0000000000000000 ffff8800d8098f00 00007fff1564969c ffff8800d87a3f50 [ 661.988031] Call Trace: [ 661.988031] [] proc_sys_call_handler+0xb3/0xc0 [ 661.988031] [] proc_sys_write+0x14/0x20 [ 661.988031] [] vfs_write+0xba/0x1e0 [ 661.988031] [] SyS_write+0x46/0xb0 [ 661.988031] [] tracesys+0xe1/0xe6 [ 661.988031] Code: 1f 84 00 00 00 00 00 48 83 bb b0 06 00 00 00 0f 84 7c 00 00 00 48 63 0d 93 6a e1 00 48 8b 83 b8 06 00 00 31 d2 41 bc 60 00 00 00 <48> f7 f1 ba 01 00 00 00 49 89 c5 48 c1 e8 02 48 85 c0 48 0f 44 Signed-off-by: Oleg Drokin CC: Rohit Seth --- mm/page_alloc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 5dba293..91d0265 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5854,7 +5854,7 @@ int percpu_pagelist_fraction_sysctl_handler(ctl_table *table, int write, int ret; ret = proc_dointvec_minmax(table, write, buffer, length, ppos); - if (!write || (ret < 0)) + if (!write || (ret < 0) || !*length) return ret; mutex_lock(&pcp_batch_high_lock); -- 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/