From 6e56830776828d8ca9897fc4429eeab47c3bb432 Mon Sep 17 00:00:00 2001
From: Florian Westphal <fw@strlen.de>
Date: Fri, 20 Jul 2018 19:30:57 +0200
Subject: [PATCH] atl1c: reserve min skb headroom
Git-commit: 6e56830776828d8ca9897fc4429eeab47c3bb432
Patch-mainline: v4.18-rc7
References: bsc#1051510

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>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/net/ethernet/atheros/atl1c/atl1c_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
index 94270f654b3b..7087b88550db 100644
--- a/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
+++ b/drivers/net/ethernet/atheros/atl1c/atl1c_main.c
@@ -1686,6 +1686,7 @@ static struct sk_buff *atl1c_alloc_skb(struct atl1c_adapter *adapter)
 	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;
-- 
2.18.0