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

[Vlastimil Babka <vbabka@suse.cz>]

On 2/10/21 4:54 PM, 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>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  fs/proc/proc_sysctl.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index d2018f70d1fa..070d2df8ab9c 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -571,7 +571,7 @@ static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter,
>  	error = -ENOMEM;
>  	if (count >= KMALLOC_MAX_SIZE)
>  		goto out;
> -	kbuf = kzalloc(count + 1, GFP_KERNEL);
> +	kbuf = kvzalloc(count + 1, GFP_KERNEL);
>  	if (!kbuf)
>  		goto out;
>  
> @@ -600,7 +600,7 @@ static ssize_t proc_sys_call_handler(struct kiocb *iocb, struct iov_iter *iter,
>  
>  	error = count;
>  out_free_buf:
> -	kfree(kbuf);
> +	kvfree(kbuf);
>  out:
>  	sysctl_head_finish(head);
>  
>