tap: Keep hdr_len in tap_get_user()

hdr_len is repeatedly used so keep it in a local variable.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20250207-tun-v6-6-fb49cf8b103e@daynix.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index 5ca6ecf0ce5fbce6777b47d9906586b07f1b690a..21b77c261fea1027a70dd1bfd5343694c90d2b61 100644 (file)
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -645,6 +645,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
        int err;
        struct virtio_net_hdr vnet_hdr = { 0 };
        int vnet_hdr_len = 0;
+       int hdr_len = 0;
        int copylen = 0;
        int depth;
        bool zerocopy = false;
@@ -663,13 +664,13 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
                if (!copy_from_iter_full(&vnet_hdr, sizeof(vnet_hdr), from))
                        goto err;
                iov_iter_advance(from, vnet_hdr_len - sizeof(vnet_hdr));
-               if ((vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) &&
-                    tap16_to_cpu(q, vnet_hdr.csum_start) +
-                    tap16_to_cpu(q, vnet_hdr.csum_offset) + 2 >
-                            tap16_to_cpu(q, vnet_hdr.hdr_len))
-                       vnet_hdr.hdr_len = cpu_to_tap16(q,
-                                tap16_to_cpu(q, vnet_hdr.csum_start) +
-                                tap16_to_cpu(q, vnet_hdr.csum_offset) + 2);
+               hdr_len = tap16_to_cpu(q, vnet_hdr.hdr_len);
+               if (vnet_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
+                       hdr_len = max(tap16_to_cpu(q, vnet_hdr.csum_start) +
+                                     tap16_to_cpu(q, vnet_hdr.csum_offset) + 2,
+                                     hdr_len);
+                       vnet_hdr.hdr_len = cpu_to_tap16(q, hdr_len);
+               }
                err = -EINVAL;
                if (tap16_to_cpu(q, vnet_hdr.hdr_len) > len)
                        goto err;
@@ -682,12 +683,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
        if (msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
                struct iov_iter i;
 
-               copylen = vnet_hdr.hdr_len ?
-                       tap16_to_cpu(q, vnet_hdr.hdr_len) : GOODCOPY_LEN;
-               if (copylen > good_linear)
-                       copylen = good_linear;
-               else if (copylen < ETH_HLEN)
-                       copylen = ETH_HLEN;
+               copylen = clamp(hdr_len ?: GOODCOPY_LEN, ETH_HLEN, good_linear);
                linear = copylen;
                i = *from;
                iov_iter_advance(&i, copylen);
@@ -697,11 +693,7 @@ static ssize_t tap_get_user(struct tap_queue *q, void *msg_control,
 
        if (!zerocopy) {
                copylen = len;
-               linear = tap16_to_cpu(q, vnet_hdr.hdr_len);
-               if (linear > good_linear)
-                       linear = good_linear;
-               else if (linear < ETH_HLEN)
-                       linear = ETH_HLEN;
+               linear = clamp(hdr_len, ETH_HLEN, good_linear);
        }
 
        skb = tap_alloc_skb(&q->sk, TAP_RESERVE, copylen,