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Date:   Tue, 4 Oct 2022 11:46:21 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     FirstName LastName <sethjenkins@google.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Alexey Dobriyan <adobriyan@gmail.com>,
        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
Message-Id: <20221004114621.7b539d2c3618b25037c4f2d0@linux-foundation.org>
In-Reply-To: <20221003224531.1930646-1-sethjenkins@google.com>
References: <20221003224531.1930646-1-sethjenkins@google.com>
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On Mon,  3 Oct 2022 18:45:31 -0400 FirstName LastName <sethjenkins@google.com> 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.
> 
> --- 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");

The current mm tree is very different here.  In fact the bug might not
exist any more.  Please take a look at the mm-stable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm?

If no fixes are needed in mm-stable then I guess the process is to
propose this patch to the stable tree maintainers.