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, 7 insertions, 11 deletions

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index 1e62b7557b00..db1521fcda5b 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -413,19 +413,15 @@ static u32 esp6_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;
+        unsigned int net_adj;
 
-        mtu -= x->props.header_len + crypto_aead_authsize(esp->aead);
-        rem = mtu & (align - 1);
-        mtu &= ~(align - 1);
-
-        if (x->props.mode != XFRM_MODE_TUNNEL) {
-                u32 padsize = ((blksize - 1) & 7) + 1;
-                mtu -= blksize - padsize;
-                mtu += min_t(u32, blksize - padsize, rem);
-        }
+        if (x->props.mode != XFRM_MODE_TUNNEL)
+                net_adj = sizeof(struct ipv6hdr);
+        else
+                net_adj = 0;
 
-        return mtu - 2;
+        return ((mtu - x->props.header_len - crypto_aead_authsize(esp->aead) -
+                 net_adj) & ~(align - 1)) + (net_adj - 2);
 }
 
 static void esp6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,