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BACKPORT: tcp: Use a struct to represent a saved_syn

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The TCP_SAVE_SYN has both the network header and tcp header.
The total length of the saved syn packet is currently stored in
the first 4 bytes (u32) of an array and the actual packet data is
stored after that.

A later patch will add a bpf helper that allows to get the tcp header
alone from the saved syn without the network header.  It will be more
convenient to have a direct offset to a specific header instead of
re-parsing it.  This requires to separately store the network hdrlen.
The total header length (i.e. network + tcp) is still needed for the
current usage in getsockopt.  Although this total length can be obtained
by looking into the tcphdr and then get the (th->doff << 2), this patch
chooses to directly store the tcp hdrlen in the second four bytes of
this newly created "struct saved_syn".  By using a new struct, it can
give a readable name to each individual header length.

Change-Id: I4ba88ba12fed185f61c74c01b4eaf7f09d26299b
Signed-off-by: Martin KaFai Lau <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Acked-by: John Fastabend <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
This commit is contained in:
Martin KaFai Lau 2020-08-20 12:00:14 -07:00 • committed by basamaryan
commit 65c272f187
No known key found for this signature in database
GPG key ID: 210D5384FB2A5885
5 changed files with 29 additions and 15 deletions
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9
net/ipv4/tcp.c
View file

@ -3699,20 +3699,21 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
lock_sock(sk);
if (tp->saved_syn) {
if (len < tp->saved_syn[0]) {
if (put_user(tp->saved_syn[0], optlen)) {
if (len < tcp_saved_syn_len(tp->saved_syn)) {
if (put_user(tcp_saved_syn_len(tp->saved_syn),
optlen)) {
release_sock(sk);
return -EFAULT;
}
release_sock(sk);
return -EINVAL;
}
len = tp->saved_syn[0];
len = tcp_saved_syn_len(tp->saved_syn);
if (put_user(len, optlen)) {
release_sock(sk);
return -EFAULT;
}
if (copy_to_user(optval, tp->saved_syn + 1, len)) {
if (copy_to_user(optval, tp->saved_syn->data, len)) {
release_sock(sk);
return -EFAULT;
}

14
net/ipv4/tcp_input.c
View file

@ -6646,13 +6646,15 @@ static void tcp_reqsk_record_syn(const struct sock *sk,
{
if (tcp_sk(sk)->save_syn) {
u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
u32 *copy;
struct saved_syn *saved_syn;
copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
if (copy) {
copy[0] = len;
memcpy(&copy[1], skb_network_header(skb), len);
req->saved_syn = copy;
saved_syn = kmalloc(struct_size(saved_syn, data, len),
GFP_ATOMIC);
if (saved_syn) {
saved_syn->network_hdrlen = skb_network_header_len(skb);
saved_syn->tcp_hdrlen = tcp_hdrlen(skb);
memcpy(saved_syn->data, skb_network_header(skb), len);
req->saved_syn = saved_syn;
}
}
}