thr3ads.net - Linux Virtualization - [PATCH] virtio_balloon: prevent uninitialized variable use [Mar 2017]

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Michael S. Tsirkin

2017-Mar-24 20:59 UTC

[PATCH] virtio_balloon: prevent uninitialized variable use

On Fri, Mar 24, 2017 at 09:40:07PM +0100, Arnd Bergmann
wrote:> On Fri, Mar 24, 2017 at 9:11 PM, Ladi Prosek <lprosek at redhat.com>
wrote:
> > On Fri, Mar 24, 2017 at 7:38 PM, David Hildenbrand <david at
redhat.com> wrote:
> >> On 23.03.2017 16:17, Arnd Bergmann wrote:
> >>> The latest gcc-7.0.1 snapshot reports a new warning:
> >>>
> >>> virtio/virtio_balloon.c: In function
'update_balloon_stats':
> >>> virtio/virtio_balloon.c:258:26: error: 'events[2]' is
used uninitialized in this function [-Werror=uninitialized]
> >>> virtio/virtio_balloon.c:260:26: error: 'events[3]' is
used uninitialized in this function [-Werror=uninitialized]
> >>> virtio/virtio_balloon.c:261:56: error: 'events[18]' is
used uninitialized in this function [-Werror=uninitialized]
> >>> virtio/virtio_balloon.c:262:56: error: 'events[17]' is
used uninitialized in this function [-Werror=uninitialized]
> >>>
> >>> This seems absolutely right, so we should add an extra check
to
> >>> prevent copying uninitialized stack data into the statistics.
> >>> From all I can tell, this has been broken since the statistics
code
> >>> was originally added in 2.6.34.
> >>>
> >>> Fixes: 9564e138b1f6 ("virtio: Add memory statistics
reporting to the balloon driver (V4)")
> >>> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> >>> ---
> >>>  drivers/virtio/virtio_balloon.c | 2 ++
> >>>  1 file changed, 2 insertions(+)
> >>>
> >>> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> >>> index 4e1191508228..cd5c54e2003d 100644
> >>> --- a/drivers/virtio/virtio_balloon.c
> >>> +++ b/drivers/virtio/virtio_balloon.c
> >>> @@ -254,12 +254,14 @@ static void update_balloon_stats(struct
virtio_balloon *vb)
> >>>
> >>>       available = si_mem_available();
> >>>
> >>> +#ifdef CONFIG_VM_EVENT_COUNTERS
> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
> >>>                               pages_to_bytes(events[PSWPIN]));
> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
> >>>                              
pages_to_bytes(events[PSWPOUT]));
> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT,
events[PGMAJFAULT]);
> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT,
events[PGFAULT]);
> >>> +#endif
> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
> >>>                               pages_to_bytes(i.freeram));
> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
> >
> > This will leave four uninitialized slots in vb->stats if
> > CONFIG_VM_EVENT_COUNTERS is not defined. update_balloon_stats should
> > have
> >
> >   BUG_ON(idx < VIRTIO_BALLOON_S_NR);
> >
> > at the end.
> >
> > You need to make sure that vb->stats is smaller, either by using
> > something else than VIRTIO_BALLOON_S_NR for its size or something else
> > than sizeof(vb->stats) as the last argument to sg_init_one in this
> > file.
> 
> Ah, got it. Would one of you create a fixed patch for this, or should I?
> 
> An easy way to solve it would be to preinitialize the events array
> and return zeroes to the host, but I don't know if that's the right
> solution.

I think that's out of spec.
> Another option would be to return 'idx' from update_balloon_stats,
> and use that for the size:
> 
> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> index cd5c54e2003d..bea3cfb88e53 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -242,7 +242,7 @@ static inline void update_stat(struct
> virtio_balloon *vb, int idx,
> 
>  #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
> 
> -static void update_balloon_stats(struct virtio_balloon *vb)
> +static unsigned int update_balloon_stats(struct virtio_balloon *vb)
>  {
>   unsigned long events[NR_VM_EVENT_ITEMS];
>   struct sysinfo i;
> @@ -268,6 +268,8 @@ static void update_balloon_stats(struct virtio_balloon
*vb)
>   pages_to_bytes(i.totalram));
>   update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
>   pages_to_bytes(available));
> +
> + return idx;
>  }
> 
>  /*
> @@ -294,13 +296,14 @@ static void stats_handle_request(struct
> virtio_balloon *vb)
>   struct virtqueue *vq;
>   struct scatterlist sg;
>   unsigned int len;
> + unsigned int num_stats;
> 
> - update_balloon_stats(vb);
> + num_stats = update_balloon_stats(vb);
> 
>   vq = vb->stats_vq;
>   if (!virtqueue_get_buf(vq, &len))
>   return;
> - sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> + sg_init_one(&sg, vb->stats, sizeof(vb->stats[0] * num_stats));
>   virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
>   virtqueue_kick(vq);
>  }
> 
>      Arnd
Sounds reasonable.

-- 
MST

Ladi Prosek

2017-Mar-27 10:02 UTC

head link

[PATCH] virtio_balloon: prevent uninitialized variable use

On Fri, Mar 24, 2017 at 9:59 PM, Michael S. Tsirkin <mst at redhat.com>
wrote:> On Fri, Mar 24, 2017 at 09:40:07PM +0100, Arnd Bergmann wrote:
>> On Fri, Mar 24, 2017 at 9:11 PM, Ladi Prosek <lprosek at
redhat.com> wrote:
>> > On Fri, Mar 24, 2017 at 7:38 PM, David Hildenbrand <david at
redhat.com> wrote:
>> >> On 23.03.2017 16:17, Arnd Bergmann wrote:
>> >>> The latest gcc-7.0.1 snapshot reports a new warning:
>> >>>
>> >>> virtio/virtio_balloon.c: In function
'update_balloon_stats':
>> >>> virtio/virtio_balloon.c:258:26: error: 'events[2]'
is used uninitialized in this function [-Werror=uninitialized]
>> >>> virtio/virtio_balloon.c:260:26: error: 'events[3]'
is used uninitialized in this function [-Werror=uninitialized]
>> >>> virtio/virtio_balloon.c:261:56: error:
'events[18]' is used uninitialized in this function
[-Werror=uninitialized]
>> >>> virtio/virtio_balloon.c:262:56: error:
'events[17]' is used uninitialized in this function
[-Werror=uninitialized]
>> >>>
>> >>> This seems absolutely right, so we should add an extra
check to
>> >>> prevent copying uninitialized stack data into the
statistics.
>> >>> From all I can tell, this has been broken since the
statistics code
>> >>> was originally added in 2.6.34.
>> >>>
>> >>> Fixes: 9564e138b1f6 ("virtio: Add memory statistics
reporting to the balloon driver (V4)")
>> >>> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
>> >>> ---
>> >>>  drivers/virtio/virtio_balloon.c | 2 ++
>> >>>  1 file changed, 2 insertions(+)
>> >>>
>> >>> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
>> >>> index 4e1191508228..cd5c54e2003d 100644
>> >>> --- a/drivers/virtio/virtio_balloon.c
>> >>> +++ b/drivers/virtio/virtio_balloon.c
>> >>> @@ -254,12 +254,14 @@ static void
update_balloon_stats(struct virtio_balloon *vb)
>> >>>
>> >>>       available = si_mem_available();
>> >>>
>> >>> +#ifdef CONFIG_VM_EVENT_COUNTERS
>> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_IN,
>> >>>                              
pages_to_bytes(events[PSWPIN]));
>> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_SWAP_OUT,
>> >>>                              
pages_to_bytes(events[PSWPOUT]));
>> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT,
events[PGMAJFAULT]);
>> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT,
events[PGFAULT]);
>> >>> +#endif
>> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMFREE,
>> >>>                               pages_to_bytes(i.freeram));
>> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
>> >
>> > This will leave four uninitialized slots in vb->stats if
>> > CONFIG_VM_EVENT_COUNTERS is not defined. update_balloon_stats
should
>> > have
>> >
>> >   BUG_ON(idx < VIRTIO_BALLOON_S_NR);
>> >
>> > at the end.
>> >
>> > You need to make sure that vb->stats is smaller, either by
using
>> > something else than VIRTIO_BALLOON_S_NR for its size or something
else
>> > than sizeof(vb->stats) as the last argument to sg_init_one in
this
>> > file.
>>
>> Ah, got it. Would one of you create a fixed patch for this, or should
I?
I will do it. If we go the route of returning 'idx' from
update_balloon_stats, my patch

   virtio_balloon: don't push uninitialized buffers to stats virtqueue

needs to be redone anyway. Thanks!
>> An easy way to solve it would be to preinitialize the events array
>> and return zeroes to the host, but I don't know if that's the
right
>> solution.
>
>
> I think that's out of spec.
>
>> Another option would be to return 'idx' from
update_balloon_stats,
>> and use that for the size:
>>
>> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
>> index cd5c54e2003d..bea3cfb88e53 100644
>> --- a/drivers/virtio/virtio_balloon.c
>> +++ b/drivers/virtio/virtio_balloon.c
>> @@ -242,7 +242,7 @@ static inline void update_stat(struct
>> virtio_balloon *vb, int idx,
>>
>>  #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
>>
>> -static void update_balloon_stats(struct virtio_balloon *vb)
>> +static unsigned int update_balloon_stats(struct virtio_balloon *vb)
>>  {
>>   unsigned long events[NR_VM_EVENT_ITEMS];
>>   struct sysinfo i;
>> @@ -268,6 +268,8 @@ static void update_balloon_stats(struct
virtio_balloon *vb)
>>   pages_to_bytes(i.totalram));
>>   update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
>>   pages_to_bytes(available));
>> +
>> + return idx;
>>  }
>>
>>  /*
>> @@ -294,13 +296,14 @@ static void stats_handle_request(struct
>> virtio_balloon *vb)
>>   struct virtqueue *vq;
>>   struct scatterlist sg;
>>   unsigned int len;
>> + unsigned int num_stats;
>>
>> - update_balloon_stats(vb);
>> + num_stats = update_balloon_stats(vb);
>>
>>   vq = vb->stats_vq;
>>   if (!virtqueue_get_buf(vq, &len))
>>   return;
>> - sg_init_one(&sg, vb->stats, sizeof(vb->stats));
>> + sg_init_one(&sg, vb->stats, sizeof(vb->stats[0] *
num_stats));
>>   virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
>>   virtqueue_kick(vq);
>>  }
>>
>>      Arnd
>
> Sounds reasonable.
>
> --
> MST

Michael S. Tsirkin

2017-Mar-28 16:18 UTC

head link

[PATCH] virtio_balloon: prevent uninitialized variable use

On Mon, Mar 27, 2017 at 12:02:33PM +0200, Ladi Prosek
wrote:> On Fri, Mar 24, 2017 at 9:59 PM, Michael S. Tsirkin <mst at
redhat.com> wrote:
> > On Fri, Mar 24, 2017 at 09:40:07PM +0100, Arnd Bergmann wrote:
> >> On Fri, Mar 24, 2017 at 9:11 PM, Ladi Prosek <lprosek at
redhat.com> wrote:
> >> > On Fri, Mar 24, 2017 at 7:38 PM, David Hildenbrand <david
at redhat.com> wrote:
> >> >> On 23.03.2017 16:17, Arnd Bergmann wrote:
> >> >>> The latest gcc-7.0.1 snapshot reports a new warning:
> >> >>>
> >> >>> virtio/virtio_balloon.c: In function
'update_balloon_stats':
> >> >>> virtio/virtio_balloon.c:258:26: error:
'events[2]' is used uninitialized in this function
[-Werror=uninitialized]
> >> >>> virtio/virtio_balloon.c:260:26: error:
'events[3]' is used uninitialized in this function
[-Werror=uninitialized]
> >> >>> virtio/virtio_balloon.c:261:56: error:
'events[18]' is used uninitialized in this function
[-Werror=uninitialized]
> >> >>> virtio/virtio_balloon.c:262:56: error:
'events[17]' is used uninitialized in this function
[-Werror=uninitialized]
> >> >>>
> >> >>> This seems absolutely right, so we should add an
extra check to
> >> >>> prevent copying uninitialized stack data into the
statistics.
> >> >>> From all I can tell, this has been broken since the
statistics code
> >> >>> was originally added in 2.6.34.
> >> >>>
> >> >>> Fixes: 9564e138b1f6 ("virtio: Add memory
statistics reporting to the balloon driver (V4)")
> >> >>> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> >> >>> ---
> >> >>>  drivers/virtio/virtio_balloon.c | 2 ++
> >> >>>  1 file changed, 2 insertions(+)
> >> >>>
> >> >>> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> >> >>> index 4e1191508228..cd5c54e2003d 100644
> >> >>> --- a/drivers/virtio/virtio_balloon.c
> >> >>> +++ b/drivers/virtio/virtio_balloon.c
> >> >>> @@ -254,12 +254,14 @@ static void
update_balloon_stats(struct virtio_balloon *vb)
> >> >>>
> >> >>>       available = si_mem_available();
> >> >>>
> >> >>> +#ifdef CONFIG_VM_EVENT_COUNTERS
> >> >>>       update_stat(vb, idx++,
VIRTIO_BALLOON_S_SWAP_IN,
> >> >>>                              
pages_to_bytes(events[PSWPIN]));
> >> >>>       update_stat(vb, idx++,
VIRTIO_BALLOON_S_SWAP_OUT,
> >> >>>                              
pages_to_bytes(events[PSWPOUT]));
> >> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MAJFLT,
events[PGMAJFAULT]);
> >> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MINFLT,
events[PGFAULT]);
> >> >>> +#endif
> >> >>>       update_stat(vb, idx++,
VIRTIO_BALLOON_S_MEMFREE,
> >> >>>                              
pages_to_bytes(i.freeram));
> >> >>>       update_stat(vb, idx++, VIRTIO_BALLOON_S_MEMTOT,
> >> >
> >> > This will leave four uninitialized slots in vb->stats if
> >> > CONFIG_VM_EVENT_COUNTERS is not defined. update_balloon_stats
should
> >> > have
> >> >
> >> >   BUG_ON(idx < VIRTIO_BALLOON_S_NR);
> >> >
> >> > at the end.
> >> >
> >> > You need to make sure that vb->stats is smaller, either by
using
> >> > something else than VIRTIO_BALLOON_S_NR for its size or
something else
> >> > than sizeof(vb->stats) as the last argument to sg_init_one
in this
> >> > file.
> >>
> >> Ah, got it. Would one of you create a fixed patch for this, or
should I?
> 
> I will do it. If we go the route of returning 'idx' from
> update_balloon_stats, my patch
> 
>    virtio_balloon: don't push uninitialized buffers to stats virtqueue
> 
> needs to be redone anyway. Thanks!
Can you do it soon pls? I'd like to do a pull request.
> >> An easy way to solve it would be to preinitialize the events array
> >> and return zeroes to the host, but I don't know if that's
the right
> >> solution.
> >
> >
> > I think that's out of spec.
> >
> >> Another option would be to return 'idx' from
update_balloon_stats,
> >> and use that for the size:
> >>
> >> diff --git a/drivers/virtio/virtio_balloon.c
b/drivers/virtio/virtio_balloon.c
> >> index cd5c54e2003d..bea3cfb88e53 100644
> >> --- a/drivers/virtio/virtio_balloon.c
> >> +++ b/drivers/virtio/virtio_balloon.c
> >> @@ -242,7 +242,7 @@ static inline void update_stat(struct
> >> virtio_balloon *vb, int idx,
> >>
> >>  #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT)
> >>
> >> -static void update_balloon_stats(struct virtio_balloon *vb)
> >> +static unsigned int update_balloon_stats(struct virtio_balloon
*vb)
> >>  {
> >>   unsigned long events[NR_VM_EVENT_ITEMS];
> >>   struct sysinfo i;
> >> @@ -268,6 +268,8 @@ static void update_balloon_stats(struct
virtio_balloon *vb)
> >>   pages_to_bytes(i.totalram));
> >>   update_stat(vb, idx++, VIRTIO_BALLOON_S_AVAIL,
> >>   pages_to_bytes(available));
> >> +
> >> + return idx;
> >>  }
> >>
> >>  /*
> >> @@ -294,13 +296,14 @@ static void stats_handle_request(struct
> >> virtio_balloon *vb)
> >>   struct virtqueue *vq;
> >>   struct scatterlist sg;
> >>   unsigned int len;
> >> + unsigned int num_stats;
> >>
> >> - update_balloon_stats(vb);
> >> + num_stats = update_balloon_stats(vb);
> >>
> >>   vq = vb->stats_vq;
> >>   if (!virtqueue_get_buf(vq, &len))
> >>   return;
> >> - sg_init_one(&sg, vb->stats, sizeof(vb->stats));
> >> + sg_init_one(&sg, vb->stats, sizeof(vb->stats[0] *
num_stats));
> >>   virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL);
> >>   virtqueue_kick(vq);
> >>  }
> >>
> >>      Arnd
> >
> > Sounds reasonable.
> >
> > --
> > MST

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