out of bounds writes in net/hsr/

out of bounds writes in net/hsr/

[Dave Jones]

I found this in coverity, and I think it's a real bug..

hsr_register_frame_in does a check that dev_idx is between 0 and 2,
therefore, a dev_idx of 2 is possible when it gets to the array writes
at the end of the function.  The arrays are defined such..

 26 struct node_entry {
...
 33         unsigned long   time_in[HSR_MAX_SLAVE];
 34         bool            time_in_stale[HSR_MAX_SLAVE];

and HSR_MAX_SLAVE is...

139 enum hsr_dev_idx {
140         HSR_DEV_NONE = -1,
141         HSR_DEV_SLAVE_A = 0,
142         HSR_DEV_SLAVE_B,
143         HSR_DEV_MASTER,
144 };
145 #define HSR_MAX_SLAVE   (HSR_DEV_SLAVE_B + 1)

So we have arrays of 2 bytes, and we can try to write to the 3rd byte.

The problem seems to be that the checking in hsr_register_frame is on
HSR_MAX_DEV which is defined as..

#define HSR_MAX_DEV     (HSR_DEV_MASTER + 1)

The + 1 seems odd, and looking at the other uses of HSR_MAX_DEV, I can't
figure out why it's there.

	Dave

Re: out of bounds writes in net/hsr/

[Arvid Brodin]

On 2014-03-04 04:27, Dave Jones wrote:
> I found this in coverity, and I think it's a real bug..
> 
> hsr_register_frame_in does a check that dev_idx is between 0 and 2,
> therefore, a dev_idx of 2 is possible when it gets to the array writes
> at the end of the function. 

Thanks for finding this; it is a bug (although I don't think it has 
actually lead to any out of bound accesses). 

However, I think you are a bit late - I believe this was fixed in a patch 
from Dan Carpenter just a few days ago. See

http://www.spinics.net/lists/netdev/msg272815.html


> #define HSR_MAX_DEV     (HSR_DEV_MASTER + 1)
> 
> The + 1 seems odd, and looking at the other uses of HSR_MAX_DEV, I can't
> figure out why it's there.
> 
> 	Dave
> 

Yes, maybe the names are a bit misleading, and they should be called something 
like HSR_DEVS and HSR_SLAVES instead. I.e.:

	some-type array-name[HSR_DEVS];

... where the last element is accessed by array-name[HSR_MAX_DEV].



-- 
Arvid Brodin | Consultant (Linux)
ALTEN | Knarrarnäsgatan 7 | SE-164 40 Kista | Sweden
arvid.brodin@alten.se | www.alten.se/en/

Re: out of bounds writes in net/hsr/

[Dave Jones]

On Tue, Mar 04, 2014 at 05:07:23PM +0100, Arvid Brodin wrote:
 > On 2014-03-04 04:27, Dave Jones wrote:
 > > I found this in coverity, and I think it's a real bug..
 > > 
 > > hsr_register_frame_in does a check that dev_idx is between 0 and 2,
 > > therefore, a dev_idx of 2 is possible when it gets to the array writes
 > > at the end of the function. 
 > 
 > Thanks for finding this; it is a bug (although I don't think it has 
 > actually lead to any out of bound accesses). 
 > 
 > However, I think you are a bit late - I believe this was fixed in a patch 
 > from Dan Carpenter just a few days ago. See
 > 
 > http://www.spinics.net/lists/netdev/msg272815.html

excellent, thanks for checking.

	Dave