xfrm: take net hdr len into account for esp payload size calculation

Corrects the function that determines the esp payload size. The calculations
done in esp{4,6}_get_mtu() lead to overlength frames in transport mode for
certain mtu values and suboptimal frames for others.

According to what is done, mainly in esp{,6}_output() and tcp_mtu_to_mss(),
net_header_len must be taken into account before doing the alignment
calculation.

Signed-off-by: Benjamin Poirier <bpoirier@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 15 deletions

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index 89a47b35905d..cb982a61536f 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -459,28 +459,22 @@ static u32 esp4_get_mtu(struct xfrm_state *x, int mtu)
         struct esp_data *esp = x->data;
         u32 blksize = ALIGN(crypto_aead_blocksize(esp->aead), 4);
         u32 align = max_t(u32, blksize, esp->padlen);
-        u32 rem;
-
-        mtu -= x->props.header_len + crypto_aead_authsize(esp->aead);
-        rem = mtu & (align - 1);
-        mtu &= ~(align - 1);
+        unsigned int net_adj;
 
         switch (x->props.mode) {
-        case XFRM_MODE_TUNNEL:
-                break;
-        default:
         case XFRM_MODE_TRANSPORT:
-                /* The worst case */
-                mtu -= blksize - 4;
-                mtu += min_t(u32, blksize - 4, rem);
-                break;
         case XFRM_MODE_BEET:
-                /* The worst case. */
-                mtu += min_t(u32, IPV4_BEET_PHMAXLEN, rem);
+                net_adj = sizeof(struct iphdr);
                 break;
+        case XFRM_MODE_TUNNEL:
+                net_adj = 0;
+                break;
+        default:
+                BUG();
         }
 
-        return mtu - 2;
+        return ((mtu - x->props.header_len - crypto_aead_authsize(esp->aead) -
+                 net_adj) & ~(align - 1)) + (net_adj - 2);
 }
 
 static void esp4_err(struct sk_buff *skb, u32 info)