openkylin
/
linux
mirror of https://gitee.com/openkylin/linux.git
9
0
Fork 0
Code Issues Projects Releases Wiki Activity

syncookies: avoid magic values and document which-bit-is-what-option 

Was a bit more difficult to read than needed due to magic shifts;
add defines and document the used encoding scheme.

Joint work with Daniel Borkmann.

Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2014-11-03 17:35:01 +01:00 committed by David S. Miller
parent 436f7c2068
commit 274e2da0ec
1 changed files with 35 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
net/ipv4/syncookies.c
View File

@ -19,10 +19,6 @@
#include <net/tcp.h>
#include <net/route.h>
/* Timestamps: lowest bits store TCP options */
#define TSBITS 6
#define TSMASK (((__u32)1 << TSBITS) - 1)
extern int sysctl_tcp_syncookies;
static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly;
@ -30,6 +26,30 @@ static u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly;
#define COOKIEBITS 24 /* Upper bits store count */
#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
/* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK
* stores TCP options:
*
* MSB LSB
* | 31 ... 6 | 5 | 4 | 3 2 1 0 |
* | Timestamp | ECN | SACK | WScale |
*
* When we receive a valid cookie-ACK, we look at the echoed tsval (if
* any) to figure out which TCP options we should use for the rebuilt
* connection.
*
* A WScale setting of '0xf' (which is an invalid scaling value)
* means that original syn did not include the TCP window scaling option.
*/
#define TS_OPT_WSCALE_MASK 0xf
#define TS_OPT_SACK BIT(4)
#define TS_OPT_ECN BIT(5)
/* There is no TS_OPT_TIMESTAMP:
* if ACK contains timestamp option, we already know it was
* requested/supported by the syn/synack exchange.
*/
#define TSBITS 6
#define TSMASK (((__u32)1 << TSBITS) - 1)
static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
ipv4_cookie_scratch);
@ -67,9 +87,11 @@ __u32 cookie_init_timestamp(struct request_sock *req)
ireq = inet_rsk(req);
options = ireq->wscale_ok ? ireq->snd_wscale : 0xf;
options |= ireq->sack_ok << 4;
options |= ireq->ecn_ok << 5;
options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK;
if (ireq->sack_ok)
options |= TS_OPT_SACK;
if (ireq->ecn_ok)
options |= TS_OPT_ECN;
ts = ts_now & ~TSMASK;
ts |= options;
@ -219,16 +241,13 @@ static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
* additional tcp options in the timestamp.
* This extracts these options from the timestamp echo.
*
* The lowest 4 bits store snd_wscale.
* next 2 bits indicate SACK and ECN support.
*
* return false if we decode an option that should not be.
*/
bool cookie_check_timestamp(struct tcp_options_received *tcp_opt,
struct net *net, bool *ecn_ok)
{
/* echoed timestamp, lowest bits contain options */
u32 options = tcp_opt->rcv_tsecr & TSMASK;
u32 options = tcp_opt->rcv_tsecr;
if (!tcp_opt->saw_tstamp) {
tcp_clear_options(tcp_opt);
@ -238,19 +257,20 @@ bool cookie_check_timestamp(struct tcp_options_received *tcp_opt,
if (!sysctl_tcp_timestamps)
return false;
tcp_opt->sack_ok = (options & (1 << 4)) ? TCP_SACK_SEEN : 0;
*ecn_ok = (options >> 5) & 1;
tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0;
*ecn_ok = options & TS_OPT_ECN;
if (*ecn_ok && !net->ipv4.sysctl_tcp_ecn)
return false;
if (tcp_opt->sack_ok && !sysctl_tcp_sack)
return false;
if ((options & 0xf) == 0xf)
if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK)
return true; /* no window scaling */
tcp_opt->wscale_ok = 1;
tcp_opt->snd_wscale = options & 0xf;
tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK;
return sysctl_tcp_window_scaling != 0;
}
EXPORT_SYMBOL(cookie_check_timestamp);