linux-kernel - Re: [PATCH][next] ovl: fix null pointer dereference on null stack pointer on error return

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Message-ID: <78e9b4ed-f530-1fd0-07a2-aca5245a6bd8@canonical.com>
Date:   Thu, 4 Jun 2020 10:27:38 +0100
From:   Colin Ian King <colin.king@...onical.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     Amir Goldstein <amir73il@...il.com>,
        overlayfs <linux-unionfs@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH][next] ovl: fix null pointer dereference on null stack
 pointer on error return

On 04/06/2020 08:25, Miklos Szeredi wrote:
> On Wed, Jun 3, 2020 at 6:15 PM Colin Ian King <colin.king@...onical.com> wrote:
>>
>> On 03/06/2020 17:11, Amir Goldstein wrote:
>>> On Wed, Jun 3, 2020 at 6:46 PM Colin King <colin.king@...onical.com> wrote:
>>>>
>>>> From: Colin Ian King <colin.king@...onical.com>
>>>>
>>>> There are two error return paths where the call to path_put is
>>>> dereferencing the null pointer 'stack'.  Fix this by avoiding the
>>>> error exit path via label 'out_err' that will lead to the path_put
>>>> calls and instead just return the error code directly.
>>>>
>>>> Addresses-Coverity: ("Dereference after null check)"
>>>> Fixes: 4155c10a0309 ("ovl: clean up getting lower layers")
>>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>>>
>>>
>>> Which branch is that based on?
>>> Doesn't seem to apply to master nor next
>>
>> It was based on today's linux-next
> 
> Yeah, it's actually
> 
> Fixes: 73819e26c0f0 ("ovl: get rid of redundant members in struct ovl_fs")
> 
> So I'll just fold your patch.  There's still a change in the loop
> count for later errors, but that's okay, since
> ovl_lower_dir()/ovl_mount_dir_noesc() use the path_put_init() variant.
> Actually ovl_lower_dir() can get rid of that path_put_init()
> completely, since now the only caller will take care of that...
> 
> Thanks for reporting!
> 
> Miklos
> 
Is there a reason for folding the fix and hence losing the Signed-off-by
tag?

Colin