linux-kernel - Re: [syzbot] WARNING in do_proc

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Date:   Mon, 3 May 2021 12:24:28 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     syzbot <syzbot+882a85c0c8ec4a3e2281@...kaller.appspotmail.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org
Subject: Re: [syzbot] WARNING in do_proc_bulk

On Mon, 3 May 2021 14:56:14 -0400 Alan Stern <stern@...land.harvard.edu> wrote:

> > 
> > do_proc_bulk() is asking kmalloc for more than MAX_ORDER bytes, in
> > 
> > 	tbuf = kmalloc(len1, GFP_KERNEL);
> 
> This doesn't seem to be a bug.  do_proc_bulk is simply trying to 
> allocate a kernel buffer for data passed to/from userspace.  If a user 
> wants too much space all at once, that's their problem.
> 
> As far as I know, the kmalloc API doesn't require the caller to filter 
> out requests for more the MAX_ORDER bytes.  Only to be prepared to 
> handle failures -- which do_proc_bulk is all set for.
> 
> Am I wrong about this?  Should we add __GFP_NOWARN to the gfp flags?

Yes, if the oversized request is a can-happen and the resulting error is handled
appropriately, __GFP_NOWARN is the way to go.