linux-kernel - Re: Linux 4.2-rc1

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Message-ID: <CACVXFVMc0YNm=GAGN7XWv-47MsT+jK6HFsMERbDgW2QM0wMsSQ@mail.gmail.com>
Date:	Thu, 9 Jul 2015 08:58:12 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Shuah Khan <shuahkhan@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: Re: Linux 4.2-rc1

On Thu, Jul 9, 2015 at 1:29 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Jul 8, 2015 at 10:17 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>>
>> Decoding the "Code:" line shows that this is the "->fw_id" dereference in
>>
>>         if (add_uevent_var(env, "FIRMWARE=%s", fw_priv->buf->fw_id))
>>                 return -ENOMEM;
>>
>> and that "fw_priv->buf" pointer is NULL.
>>
>> However, I don't see anything that looks like it should have changed
>> any of this since 4.1.
>
> Looking at the otehr uses of "fw_priv->buf", they all check that
> pointer for NULL. I see code like
>
>         fw_buf = fw_priv->buf;
>         if (!fw_buf)
>                 goto out;
>
> etc.
>
> Also, it looks like you need to hold the "fw_lock" to even look at
> that pointer, since the buffer can get reallocated etc.


Yes, the above code with holding 'fw_lock' is right fix for the issue since
sysfs read can happen anytime, and there is one race between firmware
request abort and reading uevent of sysfs.


> So that uevent code really looks buggy. It just doesn't look like a
> *new* bug to me. That code looks old, going back to 2012 and commit
> 1244691c73b2.

Exactly.

Thanks,
Ming
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