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Date:   Tue, 4 Oct 2022 15:53:41 +0300
From:   Alexey Dobriyan <adobriyan@gmail.com>
To:     sethjenkins@google.com
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
        linux-mm@kvack.org, stable@vger.kernel.org
Subject: Re: [PATCH] mm: /proc/pid/smaps_rollup: fix no vma's null-deref
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References: <20221003224531.1930646-1-sethjenkins@google.com>
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On Mon, Oct 03, 2022 at 06:45:31PM -0400, FirstName LastName wrote:
> From: Seth Jenkins <sethjenkins@google.com>
> 
> Commit 258f669e7e88 ("mm: /proc/pid/smaps_rollup: convert to single value
> seq_file") introduced a null-deref if there are no vma's in the task in
> show_smaps_rollup.
> 
> Fixes: 258f669e7e88 ("mm: /proc/pid/smaps_rollup: convert to single value seq_file")
> Cc: stable@vger.kernel.org
> Signed-off-by: Seth Jenkins <sethjenkins@google.com>

> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -969,7 +969,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
>  		vma = vma->vm_next;
>  	}
>  
> -	show_vma_header_prefix(m, priv->mm->mmap->vm_start,
> +	show_vma_header_prefix(m, priv->mm->mmap ? priv->mm->mmap->vm_start : 0,
>  			       last_vma_end, 0, 0, 0, 0);
>  	seq_pad(m, ' ');
>  	seq_puts(m, "[rollup]\n");

Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com>
Tested-by: Alexey Dobriyan <adobriyan@gmail.com>

Now I know how to create stable process without address space.