linux-kernel - Re: [PATCH] UBI: Fix crash in try_recover

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Date:   Mon, 17 Oct 2016 13:02:18 +0200
From:   Boris Brezillon <boris.brezillon@...e-electrons.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Richard Weinberger <richard@....at>,
        Brian Norris <computersforpeace@...il.com>,
        Artem Bityutskiy <dedekind1@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        MTD Maling List <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] UBI: Fix crash in try_recover_peb()

On Mon, 17 Oct 2016 10:00:25 +0200
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> Hi Boris,
> 
> On Thu, Oct 13, 2016 at 4:24 PM, Boris Brezillon
> <boris.brezillon@...e-electrons.com> wrote:
> > On Thu, 13 Oct 2016 16:05:36 +0200
> > Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> >  
> >>     drivers/mtd/ubi/eba.c: In function ‘try_recover_peb’:
> >>     drivers/mtd/ubi/eba.c:744: warning: ‘vid_hdr’ is used uninitialized in this function
> >>
> >> The pointer vid_hdr is indeed not initialized, leading to a crash when
> >> it is dereferenced.
> >>
> >> Fix this by obtaining the pointer from the VID buffer, like is done
> >> everywhere else.  
> >
> > Indeed, I don't know how I missed that one :-/.
> >  
> >>
> >> Fixes: 3291b52f9ff0acc8 ("UBI: introduce the VID buffer concept")
> >> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>  
> >
> > One minor comment below, otherwise
> >
> > Reviewed-by: Boris Brezillon <boris.brezillon@...e-electrons.com>  
> 
> Thanks!
> 
> >> ---
> >> Completely untested. And I know nothing about UBI ;-)
> >> ---
> >>  drivers/mtd/ubi/eba.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
> >> index 95c4048a371e87b6..388e46be6ad92805 100644
> >> --- a/drivers/mtd/ubi/eba.c
> >> +++ b/drivers/mtd/ubi/eba.c
> >> @@ -741,6 +741,7 @@ static int try_recover_peb(struct ubi_volume *vol, int pnum, int lnum,
> >>               goto out_put;
> >>       }
> >>
> >> +     vid_hdr = ubi_get_vid_hdr(vidb);  
> >
> > Can you move this assignment at variable declaration time?  
> 
> I can do that. However, that moves the call to ubi_get_vid_hdr() _before_
> the call to ubi_io_read_vid_hdr().
> 
> While that would still work (ubi_get_vid_hdr() would just return a pointer to
> the not-yet-read data), I think it's better to not move it, to prevent people
> from accidentally trying to use it before the data has been read.

Well, maybe. I just thought it would be safer to assign it as early as
possible to avoid another 'uninitialized var' bug if move code around
again (which will happen soon ;-)).

Anyway, it's not that important, I'll let Richard take the version
he prefers.

Thanks again for the fix.

Boris