[PATCH] UBI: Fix crash in try_recover_peb()

[PATCH] UBI: Fix crash in try_recover_peb()

[Geert Uytterhoeven]

    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.

Fixes: 3291b52f9ff0acc8 ("UBI: introduce the VID buffer concept")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
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);
 	ubi_assert(vid_hdr->vol_type == UBI_VID_DYNAMIC);
 
 	mutex_lock(&ubi->buf_mutex);
-- 
1.9.1

Re: [PATCH] UBI: Fix crash in try_recover_peb()

[Boris Brezillon]

Hi Geert,

On Thu, 13 Oct 2016 16:05:36 +0200
Geert Uytterhoeven <geert@linux-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@linux-m68k.org>

One minor comment below, otherwise

Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>

> ---
> 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?

>  	ubi_assert(vid_hdr->vol_type == UBI_VID_DYNAMIC);
>  
>  	mutex_lock(&ubi->buf_mutex);

Re: [PATCH] UBI: Fix crash in try_recover_peb()

[Boris Brezillon]

On Thu, 13 Oct 2016 16:24:58 +0200
Boris Brezillon <boris.brezillon@free-electrons.com> wrote:

> Hi Geert,
> 
> On Thu, 13 Oct 2016 16:05:36 +0200
> Geert Uytterhoeven <geert@linux-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 :-/.

That's really weird. I tried to recompile the kernel on my machine
(before applying your patch), to see if the compiler was complaining,
and it's not :-(.

I also coded simple functions with goto statements, to check that the
detection was working correctly, and it is.

Maybe you have some ideas why my compiler is failing to detect the
problem (I'm currently using the ubuntu cross-toolchain:
'arm-linux-gnueabi-gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.1) 5.4.0
20160609').

> 
> > 
> > Fixes: 3291b52f9ff0acc8 ("UBI: introduce the VID buffer concept")
> > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>  
> 
> One minor comment below, otherwise
> 
> Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> 
> > ---
> > 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?
> 
> >  	ubi_assert(vid_hdr->vol_type == UBI_VID_DYNAMIC);
> >  
> >  	mutex_lock(&ubi->buf_mutex);  
> 

Re: [PATCH] UBI: Fix crash in try_recover_peb()

[Geert Uytterhoeven]

Hi Boris,

On Thu, Oct 13, 2016 at 4:24 PM, Boris Brezillon
<boris.brezillon@free-electrons.com> wrote:
> On Thu, 13 Oct 2016 16:05:36 +0200
> Geert Uytterhoeven <geert@linux-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@linux-m68k.org>
>
> One minor comment below, otherwise
>
> Reviewed-by: Boris Brezillon <boris.brezillon@free-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.

Do you agree?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] UBI: Fix crash in try_recover_peb()

[Geert Uytterhoeven]

Hi Boris,

On Fri, Oct 14, 2016 at 12:49 PM, Boris Brezillon
<boris.brezillon@free-electrons.com> wrote:
> On Thu, 13 Oct 2016 16:24:58 +0200
> Boris Brezillon <boris.brezillon@free-electrons.com> wrote:
>> On Thu, 13 Oct 2016 16:05:36 +0200
>> Geert Uytterhoeven <geert@linux-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 :-/.
>
> That's really weird. I tried to recompile the kernel on my machine
> (before applying your patch), to see if the compiler was complaining,
> and it's not :-(.
>
> I also coded simple functions with goto statements, to check that the
> detection was working correctly, and it is.
>
> Maybe you have some ideas why my compiler is failing to detect the
> problem (I'm currently using the ubuntu cross-toolchain:
> 'arm-linux-gnueabi-gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.1) 5.4.0
> 20160609').

It depends highly on the toolchain.

My good old m68k-linux-gnu-gcc version 4.1.2 20061115 (prerelease) (Ubuntu
4.1.1-21) is known to generate plenty of warnings like these. Due to the high
percentage of false positives, this was disabled in later versions of gcc, but
(partially) re-enabled later (usually Arnd catches most of these while stll in
-next. I'm afraid he's suffering from travelling to Linaro Connect ;-)
Still, some of them are real bugs, so that's when my patch habits kick in...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: [PATCH] UBI: Fix crash in try_recover_peb()

[Boris Brezillon]

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

> Hi Boris,
> 
> On Thu, Oct 13, 2016 at 4:24 PM, Boris Brezillon
> <boris.brezillon@free-electrons.com> wrote:
> > On Thu, 13 Oct 2016 16:05:36 +0200
> > Geert Uytterhoeven <geert@linux-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@linux-m68k.org>  
> >
> > One minor comment below, otherwise
> >
> > Reviewed-by: Boris Brezillon <boris.brezillon@free-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

Re: [PATCH] UBI: Fix crash in try_recover_peb()

[Geert Uytterhoeven]

Hi Boris,

On Mon, Oct 17, 2016 at 1:02 PM, Boris Brezillon
<boris.brezillon@free-electrons.com> wrote:
> On Mon, 17 Oct 2016 10:00:25 +0200
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>> On Thu, Oct 13, 2016 at 4:24 PM, Boris Brezillon
>> <boris.brezillon@free-electrons.com> wrote:
>> > On Thu, 13 Oct 2016 16:05:36 +0200
>> > Geert Uytterhoeven <geert@linux-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@linux-m68k.org>
>> >
>> > One minor comment below, otherwise
>> >
>> > Reviewed-by: Boris Brezillon <boris.brezillon@free-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 ;-)).

I prefer seeing the warning again (I _will_ notice if it pops up again!) over
failing at runtime because the data structure it points to hasn't been
initialized yet, which the compiler can't warn me about...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds