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tcp: constify tcp_make_synack() socket argument 

listener socket is not locked when tcp_make_synack() is called.

We better make sure no field is written.

There is one exception : Since SYNACK packets are attached to the listener
at this moment (or SYN_RECV child in case of Fast Open),
sock_wmalloc() needs to update sk->sk_wmem_alloc, but this is done using
atomic operations so this is safe.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2015-09-25 07:39:19 -07:00 committed by David S. Miller
parent 6ac705b180
commit 5d062de7f8
2 changed files with 16 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/net/tcp.h
View File

@ -461,7 +461,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
int tcp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
int tcp_connect(struct sock *sk);
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
struct request_sock *req,
struct tcp_fastopen_cookie *foc);
int tcp_disconnect(struct sock *sk, int flags);

24
net/ipv4/tcp_output.c
View File

@ -2944,20 +2944,25 @@ int tcp_send_synack(struct sock *sk)
* Allocate one skb and build a SYNACK packet.
* @dst is consumed : Caller should not use it again.
*/
struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
struct sk_buff *tcp_make_synack(const struct sock *sk, struct dst_entry *dst,
struct request_sock *req,
struct tcp_fastopen_cookie *foc)
{
struct tcp_out_options opts;
struct inet_request_sock *ireq = inet_rsk(req);
struct tcp_sock *tp = tcp_sk(sk);
struct tcphdr *th;
struct sk_buff *skb;
const struct tcp_sock *tp = tcp_sk(sk);
struct tcp_md5sig_key *md5 = NULL;
struct tcp_out_options opts;
struct sk_buff *skb;
int tcp_header_size;
struct tcphdr *th;
u16 user_mss;
int mss;
skb = sock_wmalloc(sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
/* sk is a const pointer, because we want to express multiple cpus
* might call us concurrently.
* sock_wmalloc() will change sk->sk_wmem_alloc in an atomic way.
*/
skb = sock_wmalloc((struct sock *)sk, MAX_TCP_HEADER, 1, GFP_ATOMIC);
if (unlikely(!skb)) {
dst_release(dst);
return NULL;
@ -2968,8 +2973,9 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
skb_dst_set(skb, dst);
mss = dst_metric_advmss(dst);
if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)
mss = tp->rx_opt.user_mss;
user_mss = READ_ONCE(tp->rx_opt.user_mss);
if (user_mss && user_mss < mss)
mss = user_mss;
memset(&opts, 0, sizeof(opts));
#ifdef CONFIG_SYN_COOKIES
@ -3009,7 +3015,7 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,
/* RFC1323: The window in SYN & SYN/ACK segments is never scaled. */
th->window = htons(min(req->rcv_wnd, 65535U));
tcp_options_write((__be32 *)(th + 1), tp, &opts);
tcp_options_write((__be32 *)(th + 1), NULL, &opts);
th->doff = (tcp_header_size >> 2);
TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_OUTSEGS);