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

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Ladi Prosek

2017-Mar-24 20:11 UTC

[PATCH] virtio_balloon: prevent uninitialized variable use

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.
> CC'ing Ladi
Thanks!
> --
>
> Thanks,
>
> David

Arnd Bergmann

2017-Mar-24 20:40 UTC

head link

[PATCH] virtio_balloon: prevent uninitialized variable use

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.

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

Michael S. Tsirkin

2017-Mar-24 20:59 UTC

head link

[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

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