Re: [PATCH] proc: use vmalloc for our kernel buffer

From: Josef Bacik <josef@toxicpanda.com>
To: David Laight <David.Laight@ACULAB.COM>, "hch@lst.de" <hch@lst.de>,
	"viro@ZenIV.linux.org.uk" <viro@ZenIV.linux.org.uk>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kernel-team@fb.com" <kernel-team@fb.com>
Subject: Re: [PATCH] proc: use vmalloc for our kernel buffer
Date: Thu, 13 Aug 2020 13:08:49 -0400	[thread overview]
Message-ID: <72ea0ff5-4706-d2e9-c2cf-c8827e576399@toxicpanda.com> (raw)
In-Reply-To: <714c8baabe1a4d0191f8cdaf6e28a32d@AcuMS.aculab.com>

On 8/13/20 12:19 PM, David Laight wrote:
> From: Josef Bacik
>> Sent: 13 August 2020 15:53
>>
>>    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.
> 
> What happens if I run 'dd bs=16M ...' ?
> 
> 	David
> 

         /* don't even try if the size is too large */
         error = -ENOMEM;
         if (count >= KMALLOC_MAX_SIZE)
                 goto out;

is above this code, thanks,

Josef