bpf/cpumap: make sure frame_size for build_skb is aligned if headroom isn't

The frame_size passed to build_skb must be aligned, else it is
possible that the embedded struct skb_shared_info gets unaligned.

For correctness make sure that xdpf->headroom in included in the
alignment. No upstream drivers can hit this, as all XDP drivers provide
an aligned headroom.  This was discovered when playing with implementing
XDP support for mvneta, which have a 2 bytes DSA header, and this
Marvell ARM64 platform didn't like doing atomic operations on an
unaligned skb_shinfo(skb)->dataref addresses.

Fixes: 1c601d829ab0 ("bpf: cpumap xdp_buff to skb conversion and allocation")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 24aac0d0f412703aba83242c3ca5fe006d702fc3..8974b3755670e37b0540f3d48ee0b29da951a341 100644 (file)
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -183,7 +183,7 @@ static struct sk_buff *cpu_map_build_skb(struct bpf_cpu_map_entry *rcpu,
         * is not at a fixed memory location, with mixed length
         * packets, which is bad for cache-line hotness.
         */
-       frame_size = SKB_DATA_ALIGN(xdpf->len) + xdpf->headroom +
+       frame_size = SKB_DATA_ALIGN(xdpf->len + xdpf->headroom) +
                SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
        pkt_data_start = xdpf->data - xdpf->headroom;