xdp: implement xdp_redirect_map for generic XDP

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.

Before commit 109980b894e9 ("bpf: don't select potentially stale
ri->map from buggy xdp progs") it could crash the kernel.  Like this
commit also check that the map_owner owner is correct before
dereferencing the map pointer.  But make sure that this API misusage
can be caught by a tracepoint. Thus, allowing userspace via
tracepoints to detect misbehaving bpf_progs.

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 <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index 862575ac8da993c48998ebc0f96772c1a4ad2d35..4e16c43fba10ab7ce958582b0b6771473dbe926a 100644 (file)
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h
@@ -138,11 +138,11 @@ DEFINE_EVENT_PRINT(xdp_redirect_template, xdp_redirect_map_err,
 
 #define _trace_xdp_redirect_map(dev, xdp, fwd, map, idx)               \
         trace_xdp_redirect_map(dev, xdp, fwd ? fwd->ifindex : 0,       \
-                               0, map, idx);
+                               0, map, idx)
 
 #define _trace_xdp_redirect_map_err(dev, xdp, fwd, map, idx, err)      \
         trace_xdp_redirect_map_err(dev, xdp, fwd ? fwd->ifindex : 0,   \
-                                   err, map, idx);
+                                   err, map, idx)
 
 #endif /* _TRACE_XDP_H */
 

diff --git a/net/core/filter.c b/net/core/filter.c
index 3a50a9b021e208e40f9ac3846bdb93b9b917ad3d..24dd33dd9f0452994623e26e3a379f0bf56190ce 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2506,21 +2506,19 @@ static int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp,
        struct redirect_info *ri = this_cpu_ptr(&redirect_info);
        const struct bpf_prog *map_owner = ri->map_owner;
        struct bpf_map *map = ri->map;
+       struct net_device *fwd = NULL;
        u32 index = ri->ifindex;
-       struct net_device *fwd;
        int err;
 
        ri->ifindex = 0;
        ri->map = NULL;
        ri->map_owner = NULL;
 
-       /* This is really only caused by a deliberately crappy
-        * BPF program, normally we would never hit that case,
-        * so no need to inform someone via tracepoints either,
-        * just bail out.
-        */
-       if (unlikely(map_owner != xdp_prog))
-               return -EINVAL;
+       if (unlikely(map_owner != xdp_prog)) {
+               err = -EFAULT;
+               map = NULL;
+               goto err;
+       }
 
        fwd = __dev_map_lookup_elem(map, index);
        if (!fwd) {
@@ -2576,13 +2574,27 @@ 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);
+       const struct bpf_prog *map_owner = ri->map_owner;
+       struct bpf_map *map = ri->map;
+       struct net_device *fwd = NULL;
        u32 index = ri->ifindex;
-       struct net_device *fwd;
        unsigned int len;
        int err = 0;
 
-       fwd = dev_get_by_index_rcu(dev_net(dev), index);
        ri->ifindex = 0;
+       ri->map = NULL;
+       ri->map_owner = NULL;
+
+       if (map) {
+               if (unlikely(map_owner != xdp_prog)) {
+                       err = -EFAULT;
+                       map = NULL;
+                       goto err;
+               }
+               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;
@@ -2600,10 +2612,12 @@ int xdp_do_generic_redirect(struct net_device *dev, struct sk_buff *skb,
        }
 
        skb->dev = fwd;
-       _trace_xdp_redirect(dev, xdp_prog, index);
+       map ? _trace_xdp_redirect_map(dev, xdp_prog, fwd, map, index)
+               : _trace_xdp_redirect(dev, xdp_prog, index);
        return 0;
 err:
-       _trace_xdp_redirect_err(dev, xdp_prog, index, err);
+       map ? _trace_xdp_redirect_map_err(dev, xdp_prog, fwd, map, index, err)
+               : _trace_xdp_redirect_err(dev, xdp_prog, index, err);
        return err;
 }
 EXPORT_SYMBOL_GPL(xdp_do_generic_redirect);