bpf: cgroup skb progs cannot access ld_abs/ind
authorDaniel Borkmann <daniel@iogearbox.net>
Tue, 6 Jun 2017 16:38:04 +0000 (18:38 +0200)
committerDavid S. Miller <davem@davemloft.net>
Tue, 6 Jun 2017 20:39:48 +0000 (16:39 -0400)
commit92046578ac88e0a93f8ef03240e6c832b0189aa7
tree3706fad432d13a5174698b4a0fd3e9d5446c5daf
parentfeec084a7cf49adb4a87bea9867fb2ba99821f48
bpf: cgroup skb progs cannot access ld_abs/ind

Commit fb9a307d11d6 ("bpf: Allow CGROUP_SKB eBPF program to
access sk_buff") enabled programs of BPF_PROG_TYPE_CGROUP_SKB
type to use ld_abs/ind instructions. However, at this point,
we cannot use them, since offsets relative to SKF_LL_OFF will
end up pointing skb_mac_header(skb) out of bounds since in the
egress path it is not yet set at that point in time, but only
after __dev_queue_xmit() did a general reset on the mac header.
bpf_internal_load_pointer_neg_helper() will then end up reading
data from a wrong offset.

BPF_PROG_TYPE_CGROUP_SKB programs can use bpf_skb_load_bytes()
already to access packet data, which is also more flexible than
the insns carried over from cBPF.

Fixes: fb9a307d11d6 ("bpf: Allow CGROUP_SKB eBPF program to access sk_buff")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Chenbo Feng <fengc@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
kernel/bpf/verifier.c