nf_flow_table_block_setup and the driver TC_SETUP_FT call can modify the flow
block cb list while they are being traversed elsewhere, causing a crash.
Add a write lock around the calls to protect readers

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 net/netfilter/nf_flow_table_offload.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
index b04645ced89b..00b522890d77 100644
--- a/net/netfilter/nf_flow_table_offload.c
+++ b/net/netfilter/nf_flow_table_offload.c
@@ -1098,6 +1098,7 @@ static int nf_flow_table_block_setup(struct nf_flowtable *flowtable,
 	struct flow_block_cb *block_cb, *next;
 	int err = 0;
 
+	down_write(&flowtable->flow_block_lock);
 	switch (cmd) {
 	case FLOW_BLOCK_BIND:
 		list_splice(&bo->cb_list, &flowtable->flow_block.cb_list);
@@ -1112,6 +1113,7 @@ static int nf_flow_table_block_setup(struct nf_flowtable *flowtable,
 		WARN_ON_ONCE(1);
 		err = -EOPNOTSUPP;
 	}
+	up_write(&flowtable->flow_block_lock);
 
 	return err;
 }
@@ -1168,7 +1170,9 @@ static int nf_flow_table_offload_cmd(struct flow_block_offload *bo,
 
 	nf_flow_table_block_offload_init(bo, dev_net(dev), cmd, flowtable,
 					 extack);
+	down_write(&flowtable->flow_block_lock);
 	err = dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_FT, bo);
+	up_write(&flowtable->flow_block_lock);
 	if (err < 0)
 		return err;
 
-- 
2.38.1

On Mon, Nov 21, 2022 at 07:26:15PM +0100, Felix Fietkau wrote:
> nf_flow_table_block_setup and the driver TC_SETUP_FT call can modify the flow
> block cb list while they are being traversed elsewhere, causing a crash.
> Add a write lock around the calls to protect readers

Applied, thanks

On 21.11.22 19:26, Felix Fietkau wrote:
> nf_flow_table_block_setup and the driver TC_SETUP_FT call can modify the flow
> block cb list while they are being traversed elsewhere, causing a crash.
> Add a write lock around the calls to protect readers
> 
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
Sorry, I forgot to add this:

Reported-by: Chad Monroe <chad.monroe@smartrg.com>

- Felix

On Mon, Nov 21, 2022 at 11:45 AM Felix Fietkau <nbd@nbd.name> wrote:
>
> On 21.11.22 19:26, Felix Fietkau wrote:
> > nf_flow_table_block_setup and the driver TC_SETUP_FT call can modify the flow
> > block cb list while they are being traversed elsewhere, causing a crash.
> > Add a write lock around the calls to protect readers
> >
> > Signed-off-by: Felix Fietkau <nbd@nbd.name>
> Sorry, I forgot to add this:
>
> Reported-by: Chad Monroe <chad.monroe@smartrg.com>
>
> - Felix

Hi Felix

Could you also add a Fixes: tag ?

Thanks.

On 21.11.22 20:47, Eric Dumazet wrote:
> On Mon, Nov 21, 2022 at 11:45 AM Felix Fietkau <nbd@nbd.name> wrote:
>>
>> On 21.11.22 19:26, Felix Fietkau wrote:
>> > nf_flow_table_block_setup and the driver TC_SETUP_FT call can modify the flow
>> > block cb list while they are being traversed elsewhere, causing a crash.
>> > Add a write lock around the calls to protect readers
>> >
>> > Signed-off-by: Felix Fietkau <nbd@nbd.name>
>> Sorry, I forgot to add this:
>>
>> Reported-by: Chad Monroe <chad.monroe@smartrg.com>
>>
>> - Felix
> 
> Hi Felix
> 
> Could you also add a Fixes: tag ?
I don't know which commit to use for that tag.

- Felix

On Mon, 21 Nov 2022 21:08:12 +0100 Felix Fietkau wrote:
> > Could you also add a Fixes: tag ?  
> 
> I don't know which commit to use for that tag.

The oldest upstream commit where the problem you're solving 
can trigger?

On 21.11.22 21:35, Jakub Kicinski wrote:
> On Mon, 21 Nov 2022 21:08:12 +0100 Felix Fietkau wrote:
>> > Could you also add a Fixes: tag ?  
>> 
>> I don't know which commit to use for that tag.
> 
> The oldest upstream commit where the problem you're solving
> can trigger?
I know, but I'm having a hard time figuring that out. The initial
version of that file came without locking. Later on some locking was
added for supporting an extra API for registering to flow table events,
but it didn't cover the cases that I'm fixing.

My guess is that the locking should have been present from the start, so:

Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")

- Felix