linux-kernel - Re: [PATCH v8 15/21] mm: Change failure of MAP

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Message-ID: <atepi7eatm6dkmybou7dsyxg5c7mrlpuhfom45xzug7lqoexc2@kwk2avbfa3vl>
Date: Tue, 3 Sep 2024 12:03:25 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Pengfei Xu <pengfei.xu@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Suren Baghdasaryan <surenb@...gle.com>,
        Matthew Wilcox <willy@...radead.org>, Vlastimil Babka <vbabka@...e.cz>,
        sidhartha.kumar@...cle.com, Bert Karwatzki <spasswolf@....de>,
        Jiri Olsa <olsajiri@...il.com>, Kees Cook <kees@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Jeff Xu <jeffxu@...omium.org>, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH v8 15/21] mm: Change failure of MAP_FIXED to restoring
 the gap on failure

* Lorenzo Stoakes <lorenzo.stoakes@...cle.com> [240903 08:27]:
> Hi Andrew - TL;DR of this is - please apply the fix patch attached below to
> fix a problem in this series, thanks! :)

Oh yes.  I should have caught this, thanks Lorenzo.

Cheers,
Liam


> ----8<----
> From 3e7decc5390b0edc462afa74794a8208e25e50f2 Mon Sep 17 00:00:00 2001
> From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Date: Tue, 3 Sep 2024 13:20:34 +0100
> Subject: [PATCH] mm: fix off-by-one error in vms_abort_munmap_vmas()
> 
> Maple tree ranges have an inclusive end, VMAs do not, so we must subtract
> one from the VMA-specific end value when using a mas_...() function.
> 
> We failed to do so in vms_abort_munmap_vmas() which resulted in a store
> overlapping the intended range by one byte, and thus corrupting the maple
> tree.
> 
> Fix this by subtracting one from vms->end() passed into mas_set_range().
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> ---
>  mm/vma.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vma.h b/mm/vma.h
> index 370d3246f147..819f994cf727 100644
> --- a/mm/vma.h
> +++ b/mm/vma.h
> @@ -240,7 +240,7 @@ static inline void vms_abort_munmap_vmas(struct vma_munmap_struct *vms,
>  	 * not symmetrical and state data has been lost.  Resort to the old
>  	 * failure method of leaving a gap where the MAP_FIXED mapping failed.
>  	 */
> -	mas_set_range(mas, vms->start, vms->end);
> +	mas_set_range(mas, vms->start, vms->end - 1);
>  	if (unlikely(mas_store_gfp(mas, NULL, GFP_KERNEL))) {
>  		pr_warn_once("%s: (%d) Unable to abort munmap() operation\n",
>  			     current->comm, current->pid);
> --
> 2.46.0