linux-kernel - [PATCH] mm: Don't warn if memdup

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Date:	Wed, 11 Jan 2012 18:50:36 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	lizf@...fujitsu.com, akpm@...ux-foundation.org, penberg@...nel.org
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Sasha Levin <levinsasha928@...il.com>
Subject: [PATCH] mm: Don't warn if memdup_user fails

memdup_user() is called when we need to copy data from userspace. This
means that a user is able to trigger warnings if the kmalloc() inside
memdup_user() fails.

For example, this is one caused by writing to much data to ecryptdev:

[  912.739685] ------------[ cut here ]------------
[  912.745080] WARNING: at mm/page_alloc.c:2217 __alloc_pages_nodemask+0x22c/0x910()
[  912.746525] Pid: 19977, comm: trinity Not tainted 3.2.0-next-20120110-sasha #120
[  912.747915] Call Trace:
[  912.748415]  [<ffffffff8115ec5c>] ? __alloc_pages_nodemask+0x22c/0x910
[  912.749651]  [<ffffffff8109a2d5>] warn_slowpath_common+0x75/0xb0
[  912.750756]  [<ffffffff8109a3d5>] warn_slowpath_null+0x15/0x20
[  912.751831]  [<ffffffff8115ec5c>] __alloc_pages_nodemask+0x22c/0x910
[  912.754230]  [<ffffffff81070fd5>] ? pvclock_clocksource_read+0x55/0xd0
[  912.755484]  [<ffffffff8106ff56>] ? kvm_clock_read+0x46/0x80
[  912.756565]  [<ffffffff810d1548>] ? sched_clock_cpu+0xc8/0x140
[  912.757667]  [<ffffffff810cc731>] ? get_parent_ip+0x11/0x50
[  912.758731]  [<ffffffff810cc731>] ? get_parent_ip+0x11/0x50
[  912.759890]  [<ffffffff81341a4b>] ? ecryptfs_miscdev_write+0x6b/0x240
[  912.761119]  [<ffffffff81196c80>] alloc_pages_current+0xa0/0x110
[  912.762269]  [<ffffffff8115ba1f>] __get_free_pages+0xf/0x40
[  912.763347]  [<ffffffff811a6082>] __kmalloc_track_caller+0x172/0x190
[  912.764561]  [<ffffffff8116f0ab>] memdup_user+0x2b/0x90
[  912.765526]  [<ffffffff81341a4b>] ecryptfs_miscdev_write+0x6b/0x240
[  912.766669]  [<ffffffff813419e0>] ? ecryptfs_miscdev_open+0x190/0x190
[  912.767832]  [<ffffffff811ba360>] do_loop_readv_writev+0x50/0x80
[  912.770735]  [<ffffffff811ba69e>] do_readv_writev+0x1ce/0x1e0
[  912.773059]  [<ffffffff8251bbbc>] ? __mutex_unlock_slowpath+0x10c/0x200
[  912.774634]  [<ffffffff810cc731>] ? get_parent_ip+0x11/0x50
[  912.775699]  [<ffffffff810cc8dd>] ? sub_preempt_count+0x9d/0xd0
[  912.776827]  [<ffffffff8251f09d>] ? retint_swapgs+0x13/0x1b
[  912.777887]  [<ffffffff811ba758>] vfs_writev+0x48/0x60
[  912.779162]  [<ffffffff811ba86f>] sys_writev+0x4f/0xb0
[  912.780152]  [<ffffffff8251f979>] system_call_fastpath+0x16/0x1b
[  912.793046] ---[ end trace 50c38c9cdee53379 ]---
[  912.793906] ecryptfs_miscdev_write: memdup_user returned error [-12]

Failing memdup_user() shouldn't be generating warnings, instead it should
be notifying userspace about the error.

Signed-off-by: Sasha Levin <levinsasha928@...il.com>
---
 mm/util.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 136ac4f..88bb4d4 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -91,7 +91,7 @@ void *memdup_user(const void __user *src, size_t len)
 	 * cause pagefault, which makes it pointless to use GFP_NOFS
 	 * or GFP_ATOMIC.
 	 */
-	p = kmalloc_track_caller(len, GFP_KERNEL);
+	p = kmalloc_track_caller(len, GFP_KERNEL | __GFP_NOWARN);
 	if (!p)
 		return ERR_PTR(-ENOMEM);
 
-- 
1.7.8.3

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