[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, 10 insertions, 3 deletions

diff --git a/net/llc/llc_station.c b/net/llc/llc_station.c
index 959e7f31833b..83da13339490 100644
--- a/net/llc/llc_station.c
+++ b/net/llc/llc_station.c
@@ -253,7 +253,8 @@ static int llc_station_ac_inc_xid_r_cnt_by_1(struct sk_buff *skb)
 static int llc_station_ac_send_null_dsap_xid_c(struct sk_buff *skb)
 {
         int rc = 1;
-        struct sk_buff *nskb = llc_alloc_frame(NULL, skb->dev);
+        struct sk_buff *nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U,
+                                               sizeof(struct llc_xid_info));
 
         if (!nskb)
                 goto out;
@@ -274,7 +275,8 @@ static int llc_station_ac_send_xid_r(struct sk_buff *skb)
 {
         u8 mac_da[ETH_ALEN], dsap;
         int rc = 1;
-        struct sk_buff* nskb = llc_alloc_frame(NULL, skb->dev);
+        struct sk_buff *nskb = llc_alloc_frame(NULL, skb->dev, LLC_PDU_TYPE_U,
+                                               sizeof(struct llc_xid_info));
 
         if (!nskb)
                 goto out;
@@ -298,7 +300,12 @@ static int llc_station_ac_send_test_r(struct sk_buff *skb)
 {
         u8 mac_da[ETH_ALEN], dsap;
         int rc = 1;
-        struct sk_buff *nskb = llc_alloc_frame(NULL, skb->dev);
+        u32 data_size;
+        struct sk_buff *nskb;
+
+        /* 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;