Commit 3dd5c330 authored by Jason Wang's avatar Jason Wang Committed by David S. Miller
Browse files

tuntap: correctly linearize skb when zerocopy is used

Userspace may produce vectors greater than MAX_SKB_FRAGS. When we try to
linearize parts of the skb to let the rest of iov to be fit in
the frags, we need count copylen into linear when calling tun_alloc_skb()
instead of partly counting it into data_len. Since this breaks
zerocopy_sg_from_iovec() since its inner counter assumes nr_frags should
be zero at beginning. This cause nr_frags to be increased wrongly without
setting the correct frags.

This bug were introduced from 0690899b

(tun: experimental zero copy tx support)

Cc: Michael S. Tsirkin <>
Signed-off-by: default avatarJason Wang <>
Acked-by: default avatarMichael S. Tsirkin <>
Signed-off-by: default avatarDavid S. Miller <>
parent 440d57bc
......@@ -1042,7 +1042,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
struct tun_pi pi = { 0, cpu_to_be16(ETH_P_IP) };
struct sk_buff *skb;
size_t len = total_len, align = NET_SKB_PAD;
size_t len = total_len, align = NET_SKB_PAD, linear;
struct virtio_net_hdr gso = { 0 };
int offset = 0;
int copylen;
......@@ -1106,10 +1106,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile,
copylen = gso.hdr_len;
if (!copylen)
copylen = GOODCOPY_LEN;
} else
linear = copylen;
} else {
copylen = len;
linear = gso.hdr_len;
skb = tun_alloc_skb(tfile, align, copylen, gso.hdr_len, noblock);
skb = tun_alloc_skb(tfile, align, copylen, linear, noblock);
if (IS_ERR(skb)) {
if (PTR_ERR(skb) != -EAGAIN)
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