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

[ Upstream commit 77ea5f4cbe2084db9ab021ba73fb7eadf1610884 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index 24aac0d..8974b37 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;