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

From: Miklos Szeredi
Date: Thu Jun 04 2020 - 03:25:19 EST

On Wed, Jun 3, 2020 at 6:15 PM Colin Ian King <colin.king@xxxxxxxxxxxxx> wrote:
> On 03/06/2020 17:11, Amir Goldstein wrote:
> > On Wed, Jun 3, 2020 at 6:46 PM Colin King <colin.king@xxxxxxxxxxxxx> wrote:
> >>
> >> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> >>
> >> 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@xxxxxxxxxxxxx>
> >
> >
> > 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!