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
xdp_redirect_map sample in SKB-mode '-S', this resulted in trying
sending on ifindex 0 which isn't valid, resulting in getting SKB
packets dropped. Thus, the reported performance numbers are wrong in
commit 24251c264798 ("samples/bpf: add option for native and skb mode
for redirect apps") for the 'xdp_redirect_map -S' case.
It might seem innocent this was lacking, but it can actually crash the
kernel. The potential crash is caused by not consuming redirect_info->map.
The bpf_redirect_map helper will set this_cpu_ptr(&redirect_info)->map
pointer, which will survive even after unloading the xdp bpf_prog and
deallocating the devmap data-structure. This leaves a dead map
pointer around. The kernel will crash when loading the xdp_redirect
sample (in native XDP mode) as it doesn't reset map (via bpf_redirect)
and returns XDP_REDIRECT, which will cause it to dereference the map
pointer.
Fixes: 6103aa96ec07 ("net: implement XDP_REDIRECT for xdp generic")
Fixes: 24251c264798 ("samples/bpf: add option for native and skb mode for
redirect apps")
Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
---
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);
+
fwd = dev_get_by_index_rcu(dev_net(dev), index);
ri->ifindex = 0;
if (unlikely(!fwd)) {
