linux-kernel - Re: [PATCH][next] mm/vmalloc: Fix read of pointer area after it has been free'd

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Message-ID: <20210329171434.GH351017@casper.infradead.org>
Date:   Mon, 29 Mar 2021 18:14:34 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Nicholas Piggin <npiggin@...il.com>, linux-mm@...ck.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] mm/vmalloc: Fix read of pointer area after it has
 been free'd

On Mon, Mar 29, 2021 at 06:07:30PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently the memory pointed to by area is being freed by the
> free_vm_area call and then area->nr_pages is referencing the
> free'd object. Fix this swapping the order of the warn_alloc
> message and the free.
> 
> Addresses-Coverity: ("Read from pointer after free")
> Fixes: 014ccf9b888d ("mm/vmalloc: improve allocation failure error messages")

i don't have this git sha.  if this is -next, the sha ids aren't stable
and shouldn't be referenced in commit logs, because these fixes should
just be squashed into the not-yet-upstream commits.

> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  mm/vmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index b73e4e715e0d..7936405749e4 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2790,11 +2790,11 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
>  	}
>  
>  	if (!pages) {
> -		free_vm_area(area);
>  		warn_alloc(gfp_mask, NULL,
>  			   "vmalloc size %lu allocation failure: "
>  			   "page array size %lu allocation failed",
>  			   area->nr_pages * PAGE_SIZE, array_size);
> +		free_vm_area(area);
>  		return NULL;

this fix looks right to me.