[PATCH] RDMA/core: Fix race when resolving IP address

[PATCH] RDMA/core: Fix race when resolving IP address

[Dag Moxnes]

Use neighbour lock when copying MAC address from neighbour data struct
in dst_fetch_ha.

When not using the lock, it is possible for the function to race with
neigh_update, causing it to copy an invalid MAC address.

It is possible to provoke this error by calling rdma_resolve_addr in a
tight loop, while deleting the corresponding ARP entry in another tight
loop.

Signed-off-by: Dag Moxnes <dag.moxnes@oracle.com>
Change-Id: I3c5f982b304457f0a83ea7def2fac70315ed38b4
---
 drivers/infiniband/core/addr.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
index 2f7d141598..e4945fd1bb 100644
--- a/drivers/infiniband/core/addr.c
+++ b/drivers/infiniband/core/addr.c
@@ -333,12 +333,16 @@ static int dst_fetch_ha(const struct dst_entry *dst,
 	if (!n)
 		return -ENODATA;
 
+	read_lock_bh(&n->lock)
 	if (!(n->nud_state & NUD_VALID)) {
-		neigh_event_send(n, NULL);
 		ret = -ENODATA;
 	} else {
 		memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
 	}
+	read_unlock_bh(&n->lock);
+
+	if (ret)
+		neigh_event_send(n, NULL);
 
 	neigh_release(n);
 
-- 
2.20.1

Re: [PATCH] RDMA/core: Fix race when resolving IP address

[Jason Gunthorpe]

On Fri, Jun 21, 2019 at 04:09:16PM +0200, Dag Moxnes wrote:
> Use neighbour lock when copying MAC address from neighbour data struct
> in dst_fetch_ha.
> 
> When not using the lock, it is possible for the function to race with
> neigh_update, causing it to copy an invalid MAC address.
> 
> It is possible to provoke this error by calling rdma_resolve_addr in a
> tight loop, while deleting the corresponding ARP entry in another tight
> loop.
> 
> Signed-off-by: Dag Moxnes <dag.moxnes@oracle.com>
> Change-Id: I3c5f982b304457f0a83ea7def2fac70315ed38b4
>  drivers/infiniband/core/addr.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
> index 2f7d141598..e4945fd1bb 100644
> +++ b/drivers/infiniband/core/addr.c
> @@ -333,12 +333,16 @@ static int dst_fetch_ha(const struct dst_entry *dst,
>  	if (!n)
>  		return -ENODATA;
>  
> +	read_lock_bh(&n->lock)
>  	if (!(n->nud_state & NUD_VALID)) {
> -		neigh_event_send(n, NULL);
>  		ret = -ENODATA;
>  	} else {
>  		memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
>  	}
> +	read_unlock_bh(&n->lock);
> +
> +	if (ret)
> +		neigh_event_send(n, NULL);
>  
>  	neigh_release(n);

Can we write this with less spaghetti please, maybe:

static int dst_fetch_ha(const struct dst_entry *dst,
			struct rdma_dev_addr *dev_addr,
			const void *daddr)
{
	struct neighbour *n;
	int ret = 0;

	n = dst_neigh_lookup(dst, daddr);
	if (!n)
		return -ENODATA;

	read_lock_bh(&n->lock);
	if (!(n->nud_state & NUD_VALID)) {
		read_unlock_bh(&n->lock);
		goto out_send;
	}
	memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
	read_unlock_bh(&n->lock);

	goto out_release;

out_send:
	neigh_event_send(n, NULL);
	ret = -ENODATA;
out_release:
	neigh_release(n);

	return ret;
}

Also, Parav should look at it.

Thanks,
Jason

Re: [PATCH] RDMA/core: Fix race when resolving IP address

[Dag Moxnes]

Hi Jason,


Thanks for the review.


On 6/21/19 4:56 PM, Jason Gunthorpe wrote:
> On Fri, Jun 21, 2019 at 04:09:16PM +0200, Dag Moxnes wrote:
>> Use neighbour lock when copying MAC address from neighbour data struct
>> in dst_fetch_ha.
>>
>> When not using the lock, it is possible for the function to race with
>> neigh_update, causing it to copy an invalid MAC address.
>>
>> It is possible to provoke this error by calling rdma_resolve_addr in a
>> tight loop, while deleting the corresponding ARP entry in another tight
>> loop.
>>
>> Signed-off-by: Dag Moxnes <dag.moxnes@oracle.com>
>> Change-Id: I3c5f982b304457f0a83ea7def2fac70315ed38b4
>>   drivers/infiniband/core/addr.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/infiniband/core/addr.c b/drivers/infiniband/core/addr.c
>> index 2f7d141598..e4945fd1bb 100644
>> +++ b/drivers/infiniband/core/addr.c
>> @@ -333,12 +333,16 @@ static int dst_fetch_ha(const struct dst_entry *dst,
>>   	if (!n)
>>   		return -ENODATA;
>>   
>> +	read_lock_bh(&n->lock)
Miising semicolon at end of statement. Sorry about that.
>>   	if (!(n->nud_state & NUD_VALID)) {
>> -		neigh_event_send(n, NULL);
>>   		ret = -ENODATA;
>>   	} else {
>>   		memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
>>   	}
>> +	read_unlock_bh(&n->lock);
>> +
>> +	if (ret)
>> +		neigh_event_send(n, NULL);
>>   
>>   	neigh_release(n);
> Can we write this with less spaghetti please, maybe:
>
> static int dst_fetch_ha(const struct dst_entry *dst,
> 			struct rdma_dev_addr *dev_addr,
> 			const void *daddr)
> {
> 	struct neighbour *n;
> 	int ret = 0;
>
> 	n = dst_neigh_lookup(dst, daddr);
> 	if (!n)
> 		return -ENODATA;
>
> 	read_lock_bh(&n->lock);
> 	if (!(n->nud_state & NUD_VALID)) {
> 		read_unlock_bh(&n->lock);
> 		goto out_send;
> 	}
> 	memcpy(dev_addr->dst_dev_addr, n->ha, MAX_ADDR_LEN);
> 	read_unlock_bh(&n->lock);
>
> 	goto out_release;
>
> out_send:
> 	neigh_event_send(n, NULL);
> 	ret = -ENODATA;
> out_release:
> 	neigh_release(n);
>
> 	return ret;
> }

Personally I find it more readable when the unlock is done in one place,

but sure, I can rewrite it the way you suggest if the reviewers agree that

that way is preferable.

Regards,

-Dag


> Also, Parav should look at it.
>
> Thanks,
> Jason