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From: Christoph Hellwig <hch@lst.de>
To: Josef Bacik <josef@toxicpanda.com>
Cc: Christoph Hellwig <hch@lst.de>,
	viro@ZenIV.linux.org.uk, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, kernel-team@fb.com,
	willy@infradead.org
Subject: Re: [PATCH][v2] proc: use vmalloc for our kernel buffer
Date: Thu, 13 Aug 2020 17:41:17 +0200	[thread overview]
Message-ID: <20200813154117.GA14149@lst.de> (raw)
In-Reply-To: <974e469e-e73d-6c3e-9167-fad003f1dfb9@toxicpanda.com>

On Thu, Aug 13, 2020 at 11:40:00AM -0400, Josef Bacik wrote:
> On 8/13/20 11:37 AM, Christoph Hellwig wrote:
>> On Thu, Aug 13, 2020 at 11:33:56AM -0400, Josef Bacik wrote:
>>> Since
>>>
>>>    sysctl: pass kernel pointers to ->proc_handler
>>>
>>> we have been pre-allocating a buffer to copy the data from the proc
>>> handlers into, and then copying that to userspace.  The problem is this
>>> just blind kmalloc()'s the buffer size passed in from the read, which in
>>> the case of our 'cat' binary was 64kib.  Order-4 allocations are not
>>> awesome, and since we can potentially allocate up to our maximum order,
>>> use vmalloc for these buffers.
>>>
>>> Fixes: 32927393dc1c ("sysctl: pass kernel pointers to ->proc_handler")
>>> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
>>> ---
>>> v1->v2:
>>> - Make vmemdup_user_nul actually do the right thing...sorry about that.
>>>
>>>   fs/proc/proc_sysctl.c  |  6 +++---
>>>   include/linux/string.h |  1 +
>>>   mm/util.c              | 27 +++++++++++++++++++++++++++
>>>   3 files changed, 31 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
>>> index 6c1166ccdaea..207ac6e6e028 100644
>>> --- a/fs/proc/proc_sysctl.c
>>> +++ b/fs/proc/proc_sysctl.c
>>> @@ -571,13 +571,13 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
>>>   		goto out;
>>>     	if (write) {
>>> -		kbuf = memdup_user_nul(ubuf, count);
>>> +		kbuf = vmemdup_user_nul(ubuf, count);
>>
>> Given that this can also do a kmalloc and thus needs to be paired
>> with kvfree shouldn't it be kvmemdup_user_nul?
>>
>
> There's an existing vmemdup_user that does kvmalloc, so I followed the 
> existing naming convention.  Do you want me to change them both?  Thanks,

I personally would, and given that it only has a few users it might
even be feasible.

  reply	other threads:[~2020-08-13 15:41 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-13 14:53 [PATCH] " Josef Bacik
2020-08-13 14:59 ` Matthew Wilcox
2020-08-13 15:08   ` Josef Bacik
2020-08-13 15:33 ` [PATCH][v2] " Josef Bacik
2020-08-13 15:37   ` Christoph Hellwig
2020-08-13 15:40     ` Josef Bacik
2020-08-13 15:41       ` Christoph Hellwig [this message]
2020-08-13 16:20         ` Al Viro
2020-08-13 17:19           ` Josef Bacik
2020-08-13 17:31             ` Al Viro
2020-08-13 17:36               ` Josef Bacik
2020-08-13 21:10             ` David Laight
2020-08-13 21:31               ` Josef Bacik
2020-08-13 16:19 ` [PATCH] " David Laight
2020-08-13 16:21   ` Al Viro
2020-08-13 17:08   ` Josef Bacik

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