Re: [PATCH][v2] proc: use vmalloc for our kernel buffer

[Josef Bacik]

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@xxxxxxxxxxxxxx>
> > ---
> > 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,

Josef