linux-kernel - Re: [Patch V2] proc: check error pointer returned by m

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Date:	Mon, 28 Mar 2011 08:46:28 +0300
From:	Anca Emanuel <anca.emanuel@...il.com>
To:	Amerigo Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org, WANG Cong <xiyou.wangcong@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric B Munson <emunson@...bm.net>,
	David Rientjes <rientjes@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Mel Gorman <mel@....ul.ie>, linux-fsdevel@...r.kernel.org
Subject: Re: [Patch V2] proc: check error pointer returned by m_start()

On Mon, Mar 28, 2011 at 8:26 AM, Amerigo Wang <amwang@...hat.com> wrote:
> From: WANG Cong <xiyou.wangcong@...il.com>
>
> V2: move the check into m_stop() as suggested by Linus,
> also, most ->show() implementations assume the second parameter 'v'
> is not NULL, this fixes them too.
>
> Anca reported a bug:
>
> [15117.080119] BUG: unable to handle kernel paging request at fffffffffffffff3
> [15117.080152] IP: [<ffffffff811b4989>] vma_stop+0x19/0x40
>
> Linus did the initial analysis, and found this was caused
> by commit ec6fd8a4355c ("report errors in /proc/*/*map*
> sanely"), which replaces NULL with various ERR_PTR() cases.
>
> This is true, that commit changed the return value of m_start(),
> which will return an error pointer on failure, but Al forgot
> to check the error pointer in m_stop() which will be called
> when m_start() fails. This patches fixes it.
>
> Reported-by: Anca Emanuel <anca.emanuel@...il.com>
> Tested-by: Anca Emanuel <anca.emanuel@...il.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: WANG Cong <amwang@...hat.com>
> Signed-off-by: WANG Cong <xiyou.wangcong@...il.com>
>
> ---
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 7c708a4..8e59169 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -124,8 +124,10 @@ static void *m_start(struct seq_file *m, loff_t *pos)
>                return ERR_PTR(-ESRCH);
>
>        mm = mm_for_maps(priv->task);
> -       if (!mm || IS_ERR(mm))
> +       if (IS_ERR_OR_NULL(mm)) {
> +               put_task_struct(priv->task);
>                return mm;
> +       }
>        down_read(&mm->mmap_sem);
>
>        tail_vma = get_gate_vma(priv->task->mm);
> @@ -182,6 +184,8 @@ static void m_stop(struct seq_file *m, void *v)
>        struct proc_maps_private *priv = m->private;
>        struct vm_area_struct *vma = v;
>
> +       if (IS_ERR_OR_NULL(v))
> +               return;

Note: this is not functional equivalent with the previous patch.

>        vma_stop(priv, vma);
>        if (priv->task)
>                put_task_struct(priv->task);
> diff --git a/fs/seq_file.c b/fs/seq_file.c
> index 05d6b0e..e17d5e6 100644
> --- a/fs/seq_file.c
> +++ b/fs/seq_file.c
> @@ -83,7 +83,7 @@ static int traverse(struct seq_file *m, loff_t offset)
>        p = m->op->start(m, &index);
>        while (p) {
>                error = PTR_ERR(p);
> -               if (IS_ERR(p))
> +               if (IS_ERR_OR_NULL(p))
>                        break;
>                error = m->op->show(m, p);
>                if (error < 0)
> --

I din't test the above patch.

Linus already have the fix in his tree.
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