linux-kernel - Re: [PATCH] staging: lustre: replace kzalloc with copy_from_user with memdup

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Message-ID: <A7B00F94-83B4-4B13-941F-90591B4BC218@intel.com>
Date:	Tue, 31 Mar 2015 22:45:10 +0000
From:	"Drokin, Oleg" <oleg.drokin@...el.com>
To:	Julia Lawall <julia.lawall@...6.fr>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	"Dhere, Chaitanya (C.)" <cvijaydh@...teon.com>,
	"Dilger, Andreas" <andreas.dilger@...el.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Xiong, Jinshan" <jinshan.xiong@...el.com>,
	"aybuke.147@...il.com" <aybuke.147@...il.com>,
	"Hammond, John" <john.hammond@...el.com>,
	"HPDD-discuss@...ts.01.org" <HPDD-discuss@...1.01.org>,
	"<devel@...verdev.osuosl.org>" <devel@...verdev.osuosl.org>,
	"<linux-kernel@...r.kernel.org> Mailing List" 
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: lustre: replace kzalloc with copy_from_user
 with memdup_user


On Mar 31, 2015, at 11:57 AM, gregkh@...uxfoundation.org wrote:

> On Tue, Mar 31, 2015 at 05:15:23PM +0200, Julia Lawall wrote:
>> On Tue, 31 Mar 2015, Dhere, Chaitanya (C.) wrote:
>> 
>>> This patch replaces kzalloc and copy_from_user with memdup_user call
>>> This change was detected with coccinelle tool
>>> 
>>> Signed-off-by: Chaitanya Dhere <cvijaydh@...teon.com>
>>> ---
>>> drivers/staging/lustre/lustre/llite/file.c |   11 +++--------
>>> 1 file changed, 3 insertions(+), 8 deletions(-)
>>> 
>>> diff --git a/drivers/staging/lustre/lustre/llite/file.c b/drivers/staging/lustre/lustre/llite/file.c
>>> index 85e74d1..85b5567 100644
>>> --- a/drivers/staging/lustre/lustre/llite/file.c
>>> +++ b/drivers/staging/lustre/lustre/llite/file.c
>>> @@ -2368,14 +2368,9 @@ ll_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>>> 		struct hsm_state_set	*hss;
>>> 		int			 rc;
>>> 
>>> -		hss = kzalloc(sizeof(*hss), GFP_NOFS);
>>> -		if (!hss)
>>> -			return -ENOMEM;
>>> -
>>> -		if (copy_from_user(hss, (char *)arg, sizeof(*hss))) {
>>> -			OBD_FREE_PTR(hss);
>>> -			return -EFAULT;
>>> -		}
>>> +		hss = memdup_user((char *)arg, sizeof(*hss));
>> 
>> memdup_user will use the flag GFP_KERNEL, ie (__GFP_WAIT | __GFP_IO |
>> __GFP_FS), rather than the flag GFP_NOFS, ie (__GFP_WAIT | __GFP_IO), that
>> is specified.  I don't know if this is a problem here.
> 
> Yes, this is a filesystem, so this can't be changed, as we can't have
> the allocation go out and ask for more filesystem accesses in the middle
> of trying to do a filesystem access :)

Technically in this place we are not really holding any locks or anything else of value to cause a deadlock,
so we might be fine here.
More importantly, I totally missed this OBD_ALLOC replacement with kzalloc when it happened.
In theory all OBD_ALLOC() calls add up all allocated memory in a counter and then OBD_FREE() calls
subtract freed memory (for a poor man's memory leak detection and tracing).
Now since it's out of match, there should have been tons of very loud warnings about it, but I don't see
any in my logs and I wonder why.

Julia, I wonder if you happen to have a bunch of other patches to get rid of the rest of OBD_ALLOC and OBD_FREE stuff by any chance?

Bye,
    Oleg--
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