On 09/06/2017 08:42 PM, John Fastabend wrote:
On 09/06/2017 11:18 AM, Jesper Dangaard Brouer wrote:
On Wed, 06 Sep 2017 18:24:07 +0200
Daniel Borkmann <[email protected]> wrote:
On 09/06/2017 05:26 PM, Jesper Dangaard Brouer wrote:
Using bpf_redirect_map is allowed for generic XDP programs, but the
appropriate map lookup was never performed in xdp_do_generic_redirect().
Instead the map-index is directly used as the ifindex. For the
Good point, but ...
[...]
net/core/filter.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/net/core/filter.c b/net/core/filter.c
index 5912c738a7b2..6a4745bf2c9f 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2562,6 +2562,32 @@ int xdp_do_redirect(struct net_device *dev, struct
xdp_buff *xdp,
}
EXPORT_SYMBOL_GPL(xdp_do_redirect);
+static int xdp_do_generic_redirect_map(struct net_device *dev,
+ struct sk_buff *skb,
+ struct bpf_prog *xdp_prog)
+{
+ struct redirect_info *ri = this_cpu_ptr(&redirect_info);
+ struct bpf_map *map = ri->map;
+ u32 index = ri->ifindex;
+ struct net_device *fwd;
+ int err;
+
+ ri->ifindex = 0;
+ ri->map = NULL;
+
+ fwd = __dev_map_lookup_elem(map, index);
+ if (!fwd) {
+ err = -EINVAL;
+ goto err;
+ }
+ skb->dev = fwd;
+ _trace_xdp_redirect_map(dev, xdp_prog, fwd, map, index);
+ return 0;
+err:
+ _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, map, index, err);
+ return err;
+}
+
int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
struct bpf_prog *xdp_prog)
{
@@ -2571,6 +2597,9 @@ int xdp_do_generic_redirect(struct net_device *dev,
struct sk_buff *skb,
unsigned int len;
int err = 0;
+ if (ri->map)
+ return xdp_do_generic_redirect_map(dev, skb, xdp_prog);
This is not quite correct. Really, the only thing you want
to do here is more or less ...
int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
struct bpf_prog *xdp_prog)
{
struct redirect_info *ri = this_cpu_ptr(&redirect_info);
struct bpf_map *map = ri->map;
u32 index = ri->ifindex;
struct net_device *fwd;
unsigned int len;
int err = 0;
ri->ifindex = 0;
ri->map = NULL;
if (map)
fwd = __dev_map_lookup_elem(map, index);
else
fwd = dev_get_by_index_rcu(dev_net(dev), index);
if (unlikely(!fwd)) {
err = -EINVAL;
goto err;
}
[...]
... such that you have a common path to also do the IFF_UP
and MTU checks that are done here, but otherwise omitted in
your patch.
Ah, yes. My patch miss the IFF_UP and MTU check. (I was too inspired by
xdp_do_redirect_map).
Otherwise it looks good, but note that it also doesn't really
resolve the issue you mention wrt stale map pointers by the
way. [...]
I actually discovered more cases where we can crash the kernel :-(
E.g. driver not supporting XDP_REDIRECT, are still allowed to load an
XDP bpf_prog that call bpf_redirect_map() and set the ->map pointer,
but it will never call xdp_do_redirect() (which is responsible for
clearing/consuming ->map pointer).
Another case: You can also call bpf_redirect_map() and then NOT return
XDP_REDIRECT (it is obviously strange, but the bpf-helper API allows it).
I think we can cover both these cases with previous suggestion to check
prog pointers. Working up a patch now.
Yep, they would both be covered.
