[LLC]: skb allocation size for responses

Allocate the skb for llc responses with the received packet size by
using the size adjustable llc_frame_alloc.
Don't allocate useless extra payload.
Cleanup magic numbers.

So, this fixes oops.
Reported by Jim Westfall:
kernel: skb_over_panic: text:c0541fc7 len:1000 put:997 head:c166ac00 data:c166ac2f tail:0xc166b017 end:0xc166ac80 dev:eth0
kernel: ------------[ cut here ]------------
kernel: kernel BUG at net/core/skbuff.c:95!

Signed-off-by: Joonwoo Park <joonwpark81@gmail.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 2 deletions

diff --git a/net/llc/llc_s_ac.c b/net/llc/llc_s_ac.c
index ac3d93b210d2..a94bd56bcac6 100644
--- a/net/llc/llc_s_ac.c
+++ b/net/llc/llc_s_ac.c
@@ -103,7 +103,8 @@ int llc_sap_action_send_xid_r(struct llc_sap *sap, struct sk_buff *skb)
         llc_pdu_decode_sa(skb, mac_da);
         llc_pdu_decode_da(skb, mac_sa);
         llc_pdu_decode_ssap(skb, &dsap);
-        nskb = llc_alloc_frame(NULL, skb->dev);
+        nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U,
+                               sizeof(struct llc_xid_info));
         if (!nskb)
                 goto out;
         llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, sap->laddr.lsap, dsap,
@@ -144,11 +145,15 @@ int llc_sap_action_send_test_r(struct llc_sap *sap, struct sk_buff *skb)
         u8 mac_da[ETH_ALEN], mac_sa[ETH_ALEN], dsap;
         struct sk_buff *nskb;
         int rc = 1;
+        u32 data_size;
 
         llc_pdu_decode_sa(skb, mac_da);
         llc_pdu_decode_da(skb, mac_sa);
         llc_pdu_decode_ssap(skb, &dsap);
-        nskb = llc_alloc_frame(NULL, skb->dev);
+
+        /* The test request command is type U (llc_len = 3) */
+        data_size = ntohs(eth_hdr(skb)->h_proto) - 3;
+        nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U, data_size);
         if (!nskb)
                 goto out;
         llc_pdu_header_init(nskb, LLC_PDU_TYPE_U, sap->laddr.lsap, dsap,