linux-kernel - Re: [PATCH] mm/vmalloc: Sanitize __get_vm

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Message-ID: <20200405192108.GA9429@pc636>
Date:   Sun, 5 Apr 2020 21:21:08 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     William Kucharski <william.kucharski@...cle.com>
Cc:     William Kucharski <william.kucharski@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, jroedel@...e.de,
        vbabka@...e.cz, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] mm/vmalloc: Sanitize __get_vm_area() arguments

On Sun, Apr 05, 2020 at 07:23:15PM +0200, Uladzislau Rezki wrote:
> On Sat, Apr 04, 2020 at 11:25:45PM -0600, William Kucharski wrote:
> > 
> > 
> > > On Apr 4, 2020, at 12:52 PM, Uladzislau Rezki <urezki@...il.com> wrote:
> > > 
> > >> 
> > >> Is there any need to similarly sanitize “size” to assure start + size doesn’t go past “end?”
> > >> 
> > > Why is that double check needed if all such tests are done deeper on stack?
> > 
> > If such tests ARE performed, then it doesn't matter to me whether it is checked before or after,
> > it just seems that nothing checks whether start + size makes some sort of sense with respect
> > to end.
> > 
> > I admit I didn't walk through all the routines to see if such a check would be superfluous.
> > 
> Yes, we check it:
> 
> <snip>
> static __always_inline bool
> is_within_this_va(struct vmap_area *va, unsigned long size,
>  unsigned long align, unsigned long vstart)
> {
>  ...
>  return (nva_start_addr + size <= va->va_end);
> }
> <snip>
> 
Sorry, was thinking about one place showed different one. Here we go:

<snip>
 /* Check the "vend" restriction. */
  if (nva_start_addr + size > vend)
    return vend;
<snip>

--
Vlad Rezki