[PATCH 3.16 277/366] atl1c: reserve min skb headroom

Ben Hutchings
2018-11-11T20:01:34Z

From: Florian Westphal <fw@strlen.de>

commit 6e56830776828d8ca9897fc4429eeab47c3bb432 upstream.

Got crash report with following backtrace:
BUG: unable to handle kernel paging request at ffff8801869daffe
RIP: 0010:[<ffffffff816429c4>] [<ffffffff816429c4>] ip6_finish_output2+0x394/0x4c0
RSP: 0018:ffff880186c83a98 EFLAGS: 00010283
RAX: ffff8801869db00e ...
[<ffffffff81644cdc>] ip6_finish_output+0x8c/0xf0
[<ffffffff81644d97>] ip6_output+0x57/0x100
[<ffffffff81643dc9>] ip6_forward+0x4b9/0x840
[<ffffffff81645566>] ip6_rcv_finish+0x66/0xc0
[<ffffffff81645db9>] ipv6_rcv+0x319/0x530
[<ffffffff815892ac>] netif_receive_skb+0x1c/0x70
[<ffffffffc0060bec>] atl1c_clean+0x1ec/0x310 [atl1c]
...

The bad access is in neigh_hh_output(), at skb->data - 16 (HH_DATA_MOD).
atl1c driver provided skb with no headroom, so 14 bytes (ethernet
header) got pulled, but then 16 are copied.

Reserve NET_SKB_PAD bytes headroom, like netdev_alloc_skb().

Compile tested only; I lack hardware.

Fixes: 7b7017642199 ("atl1c: Fix misuse of netdev_alloc_skb in refilling rx ring")
Signed-off-by: Florian Westphal <fw@strlen.de>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/net/ethernet/atheros/atl1c/atl1c_main.c | 1 +
1 file changed, 1 insertion(+)

--- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
+++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
@@ -1674,6 +1674,7 @@ static struct sk_buff *atl1c_alloc_skb(s
skb = build_skb(page_address(page) + adapter->rx_page_offset,
adapter->rx_frag_size);
if (likely(skb)) {
+ skb_reserve(skb, NET_SKB_PAD);
adapter->rx_page_offset += adapter->rx_frag_size;
if (adapter->rx_page_offset >= PAGE_SIZE)
adapter->rx_page = NULL;