[XFRM]: Optimize MTU calculation

Replace the probing based MTU estimation, which usually takes 2-3 iterations
to find a fitting value and may underestimate the MTU, by an exact calculation.

Also fix underestimation of the XFRM trailer_len, which causes unnecessary
reallocations.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 5a00aa8..e144a25 100644 (file)
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -279,7 +279,7 @@ struct xfrm_type
        xfrm_address_t          *(*local_addr)(struct xfrm_state *, xfrm_address_t *);
        xfrm_address_t          *(*remote_addr)(struct xfrm_state *, xfrm_address_t *);
        /* Estimate maximal size of result of transformation of a dgram */
-       u32                     (*get_max_size)(struct xfrm_state *, int size);
+       u32                     (*get_mtu)(struct xfrm_state *, int size);
 };
 
 extern int xfrm_register_type(struct xfrm_type *type, unsigned short family);

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index bdc65d8..a315d5d 100644 (file)
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -272,32 +272,34 @@ out:
        return -EINVAL;
 }
 
-static u32 esp4_get_max_size(struct xfrm_state *x, int mtu)
+static u32 esp4_get_mtu(struct xfrm_state *x, int mtu)
 {
        struct esp_data *esp = x->data;
        u32 blksize = ALIGN(crypto_blkcipher_blocksize(esp->conf.tfm), 4);
-       int enclen = 0;
+       u32 align = max_t(u32, blksize, esp->conf.padlen);
+       u32 rem;
+
+       mtu -= x->props.header_len + esp->auth.icv_trunc_len;
+       rem = mtu & (align - 1);
+       mtu &= ~(align - 1);
 
        switch (x->props.mode) {
        case XFRM_MODE_TUNNEL:
-               mtu = ALIGN(mtu +2, blksize);
                break;
        default:
        case XFRM_MODE_TRANSPORT:
                /* The worst case */
-               mtu = ALIGN(mtu + 2, 4) + blksize - 4;
+               mtu -= blksize - 4;
+               mtu += min_t(u32, blksize - 4, rem);
                break;
        case XFRM_MODE_BEET:
                /* The worst case. */
-               enclen = IPV4_BEET_PHMAXLEN;
-               mtu = ALIGN(mtu + enclen + 2, blksize);
+               mtu -= IPV4_BEET_PHMAXLEN;
+               mtu += min_t(u32, IPV4_BEET_PHMAXLEN, rem);
                break;
        }
 
-       if (esp->conf.padlen)
-               mtu = ALIGN(mtu, esp->conf.padlen);
-
-       return mtu + x->props.header_len + esp->auth.icv_trunc_len - enclen;
+       return mtu - 2;
 }
 
 static void esp4_err(struct sk_buff *skb, u32 info)
@@ -340,6 +342,7 @@ static int esp_init_state(struct xfrm_state *x)
 {
        struct esp_data *esp = NULL;
        struct crypto_blkcipher *tfm;
+       u32 align;
 
        /* null auth and encryption can have zero length keys */
        if (x->aalg) {
@@ -421,7 +424,10 @@ static int esp_init_state(struct xfrm_state *x)
                }
        }
        x->data = esp;
-       x->props.trailer_len = esp4_get_max_size(x, 0) - x->props.header_len;
+       align = ALIGN(crypto_blkcipher_blocksize(esp->conf.tfm), 4);
+       if (esp->conf.padlen)
+               align = max_t(u32, align, esp->conf.padlen);
+       x->props.trailer_len = align + 1 + esp->auth.icv_trunc_len;
        return 0;
 
 error:
@@ -438,7 +444,7 @@ static struct xfrm_type esp_type =
        .proto          = IPPROTO_ESP,
        .init_state     = esp_init_state,
        .destructor     = esp_destroy,
-       .get_max_size   = esp4_get_max_size,
+       .get_mtu        = esp4_get_mtu,
        .input          = esp_input,
        .output         = esp_output
 };

diff --git a/net/ipv6/esp6.c b/net/ipv6/esp6.c
index 6b76c4c..7107bb7 100644 (file)
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -235,22 +235,24 @@ out:
        return ret;
 }
 
-static u32 esp6_get_max_size(struct xfrm_state *x, int mtu)
+static u32 esp6_get_mtu(struct xfrm_state *x, int mtu)
 {
        struct esp_data *esp = x->data;
        u32 blksize = ALIGN(crypto_blkcipher_blocksize(esp->conf.tfm), 4);
+       u32 align = max_t(u32, blksize, esp->conf.padlen);
+       u32 rem;
 
-       if (x->props.mode == XFRM_MODE_TUNNEL) {
-               mtu = ALIGN(mtu + 2, blksize);
-       } else {
-               /* The worst case. */
+       mtu -= x->props.header_len + esp->auth.icv_trunc_len;
+       rem = mtu & (align - 1);
+       mtu &= ~(align - 1);
+
+       if (x->props.mode != XFRM_MODE_TUNNEL) {
                u32 padsize = ((blksize - 1) & 7) + 1;
-               mtu = ALIGN(mtu + 2, padsize) + blksize - padsize;
+               mtu -= blksize - padsize;
+               mtu += min_t(u32, blksize - padsize, rem);
        }
-       if (esp->conf.padlen)
-               mtu = ALIGN(mtu, esp->conf.padlen);
 
-       return mtu + x->props.header_len + esp->auth.icv_trunc_len;
+       return mtu - 2;
 }
 
 static void esp6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
@@ -380,7 +382,7 @@ static struct xfrm_type esp6_type =
        .proto          = IPPROTO_ESP,
        .init_state     = esp6_init_state,
        .destructor     = esp6_destroy,
-       .get_max_size   = esp6_get_max_size,
+       .get_mtu        = esp6_get_mtu,
        .input          = esp6_input,
        .output         = esp6_output,
        .hdr_offset     = xfrm6_find_1stfragopt,

diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 63a20e8..69a3600 100644 (file)
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1667,37 +1667,17 @@ void xfrm_state_delete_tunnel(struct xfrm_state *x)
 }
 EXPORT_SYMBOL(xfrm_state_delete_tunnel);
 
-/*
- * This function is NOT optimal.  For example, with ESP it will give an
- * MTU that's usually two bytes short of being optimal.  However, it will
- * usually give an answer that's a multiple of 4 provided the input is
- * also a multiple of 4.
- */
 int xfrm_state_mtu(struct xfrm_state *x, int mtu)
 {
-       int res = mtu;
-
-       res -= x->props.header_len;
-
-       for (;;) {
-               int m = res;
-
-               if (m < 68)
-                       return 68;
-
-               spin_lock_bh(&x->lock);
-               if (x->km.state == XFRM_STATE_VALID &&
-                   x->type && x->type->get_max_size)
-                       m = x->type->get_max_size(x, m);
-               else
-                       m += x->props.header_len;
-               spin_unlock_bh(&x->lock);
-
-               if (m <= mtu)
-                       break;
-               res -= (m - mtu);
-       }
+       int res;
 
+       spin_lock_bh(&x->lock);
+       if (x->km.state == XFRM_STATE_VALID &&
+           x->type && x->type->get_mtu)
+               res = x->type->get_mtu(x, mtu);
+       else
+               res = mtu;
+       spin_unlock_bh(&x->lock);
        return res;
 }