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

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Date:   Thu, 4 Jun 2020 11:39:24 +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 Thu, Jun 4, 2020 at 11:27 AM Colin Ian King <colin.king@...onical.com> wrote:
>
> 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?

I generally prefer to fold small fixes for not yet merged patches.  In
this case it's more of a personal preference, but in other cases it
might have an effect on bisectability.

Thanks,
Miklos