[PATCH net-next] ptr_ring: fix integer overflow

[PATCH net-next] ptr_ring: fix integer overflow

[Jason Wang]

We try to allocate one more entry for lockless peeking. The adding
operation may overflow which causes zero to be passed to kmalloc().
In this case, it returns ZERO_SIZE_PTR without any notice by ptr
ring. Try to do producing or consuming on such ring will lead NULL
dereference. Fix this detect and fail early.

Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
Reported-by: syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
Cc: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 include/linux/ptr_ring.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
index 9ca1726..3f99484 100644
--- a/include/linux/ptr_ring.h
+++ b/include/linux/ptr_ring.h
@@ -453,6 +453,8 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
 
 static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
 {
+	if (unlikely(size + 1 == 0))
+		return NULL;
 	/* Allocate an extra dummy element at end of ring to avoid consumer head
 	 * or produce head access past the end of the array. Possible when
 	 * producer/consumer operations and __ptr_ring_peek operations run in
-- 
2.7.4

Re: [PATCH net-next] ptr_ring: fix integer overflow

[Michael S. Tsirkin]

On Thu, Jan 25, 2018 at 03:31:42PM +0800, Jason Wang wrote:
> We try to allocate one more entry for lockless peeking. The adding
> operation may overflow which causes zero to be passed to kmalloc().
> In this case, it returns ZERO_SIZE_PTR without any notice by ptr
> ring. Try to do producing or consuming on such ring will lead NULL
> dereference. Fix this detect and fail early.
> 
> Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
> Reported-by: syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
> Cc: John Fastabend <john.fastabend@gmail.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Ugh that's just way too ugly.
I'll work on dropping the extra + 1 - but calling this
function with -1 size is the real source of the bug.
Do you know how come we do that?

> ---
>  include/linux/ptr_ring.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/ptr_ring.h b/include/linux/ptr_ring.h
> index 9ca1726..3f99484 100644
> --- a/include/linux/ptr_ring.h
> +++ b/include/linux/ptr_ring.h
> @@ -453,6 +453,8 @@ static inline int ptr_ring_consume_batched_bh(struct ptr_ring *r,
>  
>  static inline void **__ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp)
>  {
> +	if (unlikely(size + 1 == 0))
> +		return NULL;
>  	/* Allocate an extra dummy element at end of ring to avoid consumer head
>  	 * or produce head access past the end of the array. Possible when
>  	 * producer/consumer operations and __ptr_ring_peek operations run in
> -- 
> 2.7.4

Re: [PATCH net-next] ptr_ring: fix integer overflow

[Jason Wang]

On 2018年01月25日 21:45, Michael S. Tsirkin wrote:
> On Thu, Jan 25, 2018 at 03:31:42PM +0800, Jason Wang wrote:
>> We try to allocate one more entry for lockless peeking. The adding
>> operation may overflow which causes zero to be passed to kmalloc().
>> In this case, it returns ZERO_SIZE_PTR without any notice by ptr
>> ring. Try to do producing or consuming on such ring will lead NULL
>> dereference. Fix this detect and fail early.
>>
>> Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
>> Reported-by:syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
>> Cc: John Fastabend<john.fastabend@gmail.com>
>> Signed-off-by: Jason Wang<jasowang@redhat.com>
> Ugh that's just way too ugly.
> I'll work on dropping the extra + 1 - but calling this
> function with -1 size is the real source of the bug.
> Do you know how come we do that?
>

It looks e.g try to change tx_queue_len to UINT_MAX. And we probably 
can't prevent user form trying to do this?

Thanks

Re: [PATCH net-next] ptr_ring: fix integer overflow

[Michael S. Tsirkin]

On Thu, Jan 25, 2018 at 10:17:38PM +0800, Jason Wang wrote:
> 
> 
> On 2018年01月25日 21:45, Michael S. Tsirkin wrote:
> > On Thu, Jan 25, 2018 at 03:31:42PM +0800, Jason Wang wrote:
> > > We try to allocate one more entry for lockless peeking. The adding
> > > operation may overflow which causes zero to be passed to kmalloc().
> > > In this case, it returns ZERO_SIZE_PTR without any notice by ptr
> > > ring. Try to do producing or consuming on such ring will lead NULL
> > > dereference. Fix this detect and fail early.
> > > 
> > > Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
> > > Reported-by:syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
> > > Cc: John Fastabend<john.fastabend@gmail.com>
> > > Signed-off-by: Jason Wang<jasowang@redhat.com>
> > Ugh that's just way too ugly.
> > I'll work on dropping the extra + 1 - but calling this
> > function with -1 size is the real source of the bug.
> > Do you know how come we do that?
> > 
> 
> It looks e.g try to change tx_queue_len to UINT_MAX. And we probably can't
> prevent user form trying to do this?
> 
> Thanks

Right. BTW why net-next? Isn't the crash exploitable in net?

Re: [PATCH net-next] ptr_ring: fix integer overflow

[Jason Wang]

On 2018年01月26日 01:31, Michael S. Tsirkin wrote:
> On Thu, Jan 25, 2018 at 10:17:38PM +0800, Jason Wang wrote:
>>
>> On 2018年01月25日 21:45, Michael S. Tsirkin wrote:
>>> On Thu, Jan 25, 2018 at 03:31:42PM +0800, Jason Wang wrote:
>>>> We try to allocate one more entry for lockless peeking. The adding
>>>> operation may overflow which causes zero to be passed to kmalloc().
>>>> In this case, it returns ZERO_SIZE_PTR without any notice by ptr
>>>> ring. Try to do producing or consuming on such ring will lead NULL
>>>> dereference. Fix this detect and fail early.
>>>>
>>>> Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
>>>> Reported-by:syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
>>>> Cc: John Fastabend<john.fastabend@gmail.com>
>>>> Signed-off-by: Jason Wang<jasowang@redhat.com>
>>> Ugh that's just way too ugly.
>>> I'll work on dropping the extra + 1 - but calling this
>>> function with -1 size is the real source of the bug.
>>> Do you know how come we do that?
>>>
>> It looks e.g try to change tx_queue_len to UINT_MAX. And we probably can't
>> prevent user form trying to do this?
>>
>> Thanks
> Right. BTW why net-next? Isn't the crash exploitable in net?
>

Commit bcecb4bbf88a exists only in net-next. And in net we check r->size 
before trying to dereference the queue.

Thanks

Re: [PATCH net-next] ptr_ring: fix integer overflow

[Michael S. Tsirkin]

On Fri, Jan 26, 2018 at 11:44:22AM +0800, Jason Wang wrote:
> 
> 
> On 2018年01月26日 01:31, Michael S. Tsirkin wrote:
> > On Thu, Jan 25, 2018 at 10:17:38PM +0800, Jason Wang wrote:
> > > 
> > > On 2018年01月25日 21:45, Michael S. Tsirkin wrote:
> > > > On Thu, Jan 25, 2018 at 03:31:42PM +0800, Jason Wang wrote:
> > > > > We try to allocate one more entry for lockless peeking. The adding
> > > > > operation may overflow which causes zero to be passed to kmalloc().
> > > > > In this case, it returns ZERO_SIZE_PTR without any notice by ptr
> > > > > ring. Try to do producing or consuming on such ring will lead NULL
> > > > > dereference. Fix this detect and fail early.
> > > > > 
> > > > > Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
> > > > > Reported-by:syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
> > > > > Cc: John Fastabend<john.fastabend@gmail.com>
> > > > > Signed-off-by: Jason Wang<jasowang@redhat.com>
> > > > Ugh that's just way too ugly.
> > > > I'll work on dropping the extra + 1 - but calling this
> > > > function with -1 size is the real source of the bug.
> > > > Do you know how come we do that?
> > > > 
> > > It looks e.g try to change tx_queue_len to UINT_MAX. And we probably can't
> > > prevent user form trying to do this?
> > > 
> > > Thanks
> > Right. BTW why net-next? Isn't the crash exploitable in net?
> > 
> 
> Commit bcecb4bbf88a exists only in net-next.

Right you are.

> And in net we check r->size
> before trying to dereference the queue.
> 
> Thanks

I was wondering what it's about btw. Does anyone really create 0 size rings?

-- 
MST

Re: [PATCH net-next] ptr_ring: fix integer overflow

[David Miller]

From: Jason Wang <jasowang@redhat.com>
Date: Thu, 25 Jan 2018 15:31:42 +0800

> We try to allocate one more entry for lockless peeking. The adding
> operation may overflow which causes zero to be passed to kmalloc().
> In this case, it returns ZERO_SIZE_PTR without any notice by ptr
> ring. Try to do producing or consuming on such ring will lead NULL
> dereference. Fix this detect and fail early.
> 
> Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
> Reported-by: syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
> Cc: John Fastabend <john.fastabend@gmail.com>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

I'm dropping this because I am to understand that Michael Tsirkin's patch
series covers this issue.

Let me know if I still need to apply this.

Thanks.

Re: [PATCH net-next] ptr_ring: fix integer overflow

[Jason Wang]

On 2018年01月30日 01:01, David Miller wrote:
> From: Jason Wang <jasowang@redhat.com>
> Date: Thu, 25 Jan 2018 15:31:42 +0800
>
>> We try to allocate one more entry for lockless peeking. The adding
>> operation may overflow which causes zero to be passed to kmalloc().
>> In this case, it returns ZERO_SIZE_PTR without any notice by ptr
>> ring. Try to do producing or consuming on such ring will lead NULL
>> dereference. Fix this detect and fail early.
>>
>> Fixes: bcecb4bbf88a ("net: ptr_ring: otherwise safe empty checks can overrun array bounds")
>> Reported-by: syzbot+87678bcf753b44c39b67@syzkaller.appspotmail.com
>> Cc: John Fastabend <john.fastabend@gmail.com>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
> I'm dropping this because I am to understand that Michael Tsirkin's patch
> series covers this issue.

Yes.

>
> Let me know if I still need to apply this.
>
> Thanks.

No need for this.

Thanks