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

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Message-ID: <CAJfpegsyGmJYHJr8rmRTxScYGyNQ1ZdPMxprW1zoQmGhXg1wuA@mail.gmail.com>
Date:   Thu, 4 Jun 2020 09:25:04 +0200
From:   Miklos Szeredi <miklos@...redi.hu>
To:     Colin Ian King <colin.king@...onical.com>
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 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