Re: [PATCH] mm: Don't warn if memdup_user fails

Pekka Enberg
2012-01-12T06:43:43Z

On Wed, 11 Jan 2012, Sasha Levin wrote:
>> 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@gmail.com>

On Wed, 11 Jan 2012, David Rientjes wrote:
> Acked-by: David Rientjes <rientjes@google.com>

Acked-by: Pekka Enberg <penberg@kernel.org>

Sasha, I suppose strndup_user() has the same kind of issue?