[PATCH v4 net 01/11] xsk: tighten UMEM headroom validation to account for tailroom and min frame

The current headroom validation in xdp_umem_reg() could leave us with
insufficient space dedicated to even receive minimum-sized ethernet
frame. Furthermore if multi-buffer would come to play then
skb_shared_info stored at the end of XSK frame would be corrupted.

HW typically works with 128-aligned sizes so let us provide this value
as bare minimum.

Multi-buffer setting is known later in the configuration process so
besides accounting for 128 bytes, let us also take care of tailroom space
upfront.

Reviewed-by: Björn Töpel <bjorn@kernel.org>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Fixes: 99e3a236dd43 ("xsk: Add missing check on user supplied headroom size")
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
---
 net/xdp/xdp_umem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
index 066ce07c506d..58da2f4f4397 100644
--- a/net/xdp/xdp_umem.c
+++ b/net/xdp/xdp_umem.c

@@ -203,7 +203,8 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
 	if (!unaligned_chunks && chunks_rem)
 		return -EINVAL;
 
-	if (headroom >= chunk_size - XDP_PACKET_HEADROOM)
+	if (headroom > chunk_size - XDP_PACKET_HEADROOM -
+		       SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) - 128)
 		return -EINVAL;
 
 	if (mr->flags & XDP_UMEM_TX_METADATA_LEN) {

-- 
2.43.0