On 09/07/2017 02:33 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
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>
---
include/trace/events/xdp.h | 4 ++--
net/core/filter.c | 14 +++++++++++---
2 files changed, 13 insertions(+), 5 deletions(-)
diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index 862575ac8da9..4e16c43fba10 100644
--- 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 5912c738a7b2..3767470cab6c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2566,13 +2566,19 @@ 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;
- fwd = dev_get_by_index_rcu(dev_net(dev), index);
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;
@@ -2590,10 +2596,12 @@ int xdp_do_generic_redirect(struct net_device *dev,
struct sk_buff *skb,
}
skb->dev = fwd;
Looks much better above, thanks!
- _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);
Could we rather make this in a way such that when the two
tracepoints are disabled and thus patched out, that we can
also omit the extra conditional which has no purpose then?
Perhaps just a consolidated _trace_xdp_generic_redirect_map()
would be better to avoid this altogether given we have twice
the same anyway, here and in err path.
Thanks,
Daniel
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);
