linux-kernel - [PATCH net v3 3/9] tun: Keep hdr_len in tun_get

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Message-Id: <20250116-tun-v3-3-c6b2871e97f7@daynix.com>
Date: Thu, 16 Jan 2025 17:08:06 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Jonathan Corbet <corbet@....net>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Jason Wang <jasowang@...hat.com>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>, 
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 netdev@...r.kernel.org, kvm@...r.kernel.org, 
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
 Yuri Benditovich <yuri.benditovich@...nix.com>, 
 Andrew Melnychenko <andrew@...nix.com>, 
 Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com, 
 devel@...nix.com, Akihiko Odaki <akihiko.odaki@...nix.com>
Subject: [PATCH net v3 3/9] tun: Keep hdr_len in tun_get_user()

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

Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
---
 drivers/net/tun.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index bd272b4736fb..ec56ac865848 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1746,6 +1746,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	struct virtio_net_hdr gso = { 0 };
 	int good_linear;
 	int copylen;
+	int hdr_len = 0;
 	bool zerocopy = false;
 	int err;
 	u32 rxhash = 0;
@@ -1776,6 +1777,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,

 		if (tun16_to_cpu(tun, gso.hdr_len) > iov_iter_count(from))
 			return -EINVAL;
+		hdr_len = tun16_to_cpu(tun, gso.hdr_len);
 		iov_iter_advance(from, vnet_hdr_sz - sizeof(gso));
 	}

@@ -1783,8 +1785,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,

 	if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) {
 		align += NET_IP_ALIGN;
-		if (unlikely(len < ETH_HLEN ||
-			     (gso.hdr_len && tun16_to_cpu(tun, gso.hdr_len) < ETH_HLEN)))
+		if (unlikely(len < ETH_HLEN || (hdr_len && hdr_len < ETH_HLEN)))
 			return -EINVAL;
 	}

@@ -1797,9 +1798,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 		 * enough room for skb expand head in case it is used.
 		 * The rest of the buffer is mapped from userspace.
 		 */
-		copylen = gso.hdr_len ? tun16_to_cpu(tun, gso.hdr_len) : GOODCOPY_LEN;
-		if (copylen > good_linear)
-			copylen = good_linear;
+		copylen = min(hdr_len ? hdr_len : GOODCOPY_LEN, good_linear);
 		linear = copylen;
 		iov_iter_advance(&i, copylen);
 		if (iov_iter_npages(&i, INT_MAX) <= MAX_SKB_FRAGS)
@@ -1820,10 +1819,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
 	} else {
 		if (!zerocopy) {
 			copylen = len;
-			if (tun16_to_cpu(tun, gso.hdr_len) > good_linear)
-				linear = good_linear;
-			else
-				linear = tun16_to_cpu(tun, gso.hdr_len);
+			linear = min(hdr_len, good_linear);
 		}

 		if (frags) {

-- 
2.47.1