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net: fastopen: robustness and endianness fixes for SipHash

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Some changes to the TCP fastopen code to make it more robust
against future changes in the choice of key/cookie size, etc.

- Instead of keeping the SipHash key in an untyped u8[] buffer
  and casting it to the right type upon use, use the correct
  type directly. This ensures that the key will appear at the
  correct alignment if we ever change the way these data
  structures are allocated. (Currently, they are only allocated
  via kmalloc so they always appear at the correct alignment)

- Use DIV_ROUND_UP when sizing the u64[] array to hold the
  cookie, so it is always of sufficient size, even if
  TCP_FASTOPEN_COOKIE_MAX is no longer a multiple of 8.

- Drop the 'len' parameter from the tcp_fastopen_reset_cipher()
  function, which is no longer used.

- Add endian swabbing when setting the keys and calculating the hash,
  to ensure that cookie values are the same for a given key and
  source/destination address pair regardless of the endianness of
  the server.

Note that none of these are functional changes wrt the current
state of the code, with the exception of the swabbing, which only
affects big endian systems.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ard Biesheuvel 2019-06-19 23:46:28 +02:00 committed by David S. Miller
parent 92ad6325cb
commit 438ac88009
5 changed files with 24 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/tcp.h
View File

@ -58,7 +58,7 @@ static inline unsigned int tcp_optlen(const struct sk_buff *skb)
/* TCP Fast Open Cookie as stored in memory */
struct tcp_fastopen_cookie {
u64 val[TCP_FASTOPEN_COOKIE_MAX / sizeof(u64)];
__le64 val[DIV_ROUND_UP(TCP_FASTOPEN_COOKIE_MAX, sizeof(u64))];
s8 len;
bool exp; /* In RFC6994 experimental option format */
};

8
include/net/tcp.h
View File

@ -43,6 +43,7 @@
#include <linux/seq_file.h>
#include <linux/memcontrol.h>
#include <linux/bpf-cgroup.h>
#include <linux/siphash.h>
extern struct inet_hashinfo tcp_hashinfo;
@ -1612,8 +1613,7 @@ void tcp_free_fastopen_req(struct tcp_sock *tp);
void tcp_fastopen_destroy_cipher(struct sock *sk);
void tcp_fastopen_ctx_destroy(struct net *net);
int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
void *primary_key, void *backup_key,
unsigned int len);
void *primary_key, void *backup_key);
void tcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb);
struct sock *tcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
@ -1623,14 +1623,14 @@ void tcp_fastopen_init_key_once(struct net *net);
bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
struct tcp_fastopen_cookie *cookie);
bool tcp_fastopen_defer_connect(struct sock *sk, int *err);
#define TCP_FASTOPEN_KEY_LENGTH 16
#define TCP_FASTOPEN_KEY_LENGTH sizeof(siphash_key_t)
#define TCP_FASTOPEN_KEY_MAX 2
#define TCP_FASTOPEN_KEY_BUF_LENGTH \
(TCP_FASTOPEN_KEY_LENGTH * TCP_FASTOPEN_KEY_MAX)
/* Fastopen key context */
struct tcp_fastopen_context {
__u8 key[TCP_FASTOPEN_KEY_MAX][TCP_FASTOPEN_KEY_LENGTH];
siphash_key_t key[TCP_FASTOPEN_KEY_MAX];
int num;
struct rcu_head rcu;
};

3
net/ipv4/sysctl_net_ipv4.c
View File

@ -365,8 +365,7 @@ static int proc_tcp_fastopen_key(struct ctl_table *table, int write,
}
}
tcp_fastopen_reset_cipher(net, NULL, key,
backup_data ? key + 4 : NULL,
TCP_FASTOPEN_KEY_LENGTH);
backup_data ? key + 4 : NULL);
}
bad_key:

3
net/ipv4/tcp.c
View File

@ -2822,8 +2822,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
if (optlen == TCP_FASTOPEN_KEY_BUF_LENGTH)
backup_key = key + TCP_FASTOPEN_KEY_LENGTH;
return tcp_fastopen_reset_cipher(net, sk, key, backup_key,
TCP_FASTOPEN_KEY_LENGTH);
return tcp_fastopen_reset_cipher(net, sk, key, backup_key);
}
default:
/* fallthru */

35
net/ipv4/tcp_fastopen.c
View File

@ -7,7 +7,6 @@
#include <linux/tcp.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/siphash.h>
#include <net/inetpeer.h>
#include <net/tcp.h>
@ -31,7 +30,7 @@ void tcp_fastopen_init_key_once(struct net *net)
* for a valid cookie, so this is an acceptable risk.
*/
get_random_bytes(key, sizeof(key));
tcp_fastopen_reset_cipher(net, NULL, key, NULL, sizeof(key));
tcp_fastopen_reset_cipher(net, NULL, key, NULL);
}
static void tcp_fastopen_ctx_free(struct rcu_head *head)
@ -68,8 +67,7 @@ void tcp_fastopen_ctx_destroy(struct net *net)
}
int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
void *primary_key, void *backup_key,
unsigned int len)
void *primary_key, void *backup_key)
{
struct tcp_fastopen_context *ctx, *octx;
struct fastopen_queue *q;
@ -81,9 +79,11 @@ int tcp_fastopen_reset_cipher(struct net *net, struct sock *sk,
goto out;
}
memcpy(ctx->key[0], primary_key, len);
ctx->key[0].key[0] = get_unaligned_le64(primary_key);
ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);
if (backup_key) {
memcpy(ctx->key[1], backup_key, len);
ctx->key[1].key[0] = get_unaligned_le64(backup_key);
ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);
ctx->num = 2;
} else {
ctx->num = 1;
@ -110,19 +110,18 @@ out:
static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
struct sk_buff *syn,
const u8 *key,
const siphash_key_t *key,
struct tcp_fastopen_cookie *foc)
{
BUILD_BUG_ON(TCP_FASTOPEN_KEY_LENGTH != sizeof(siphash_key_t));
BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));
if (req->rsk_ops->family == AF_INET) {
const struct iphdr *iph = ip_hdr(syn);
foc->val[0] = siphash(&iph->saddr,
sizeof(iph->saddr) +
sizeof(iph->daddr),
(const siphash_key_t *)key);
foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
sizeof(iph->saddr) +
sizeof(iph->daddr),
key));
foc->len = TCP_FASTOPEN_COOKIE_SIZE;
return true;
}
@ -130,10 +129,10 @@ static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
if (req->rsk_ops->family == AF_INET6) {
const struct ipv6hdr *ip6h = ipv6_hdr(syn);
foc->val[0] = siphash(&ip6h->saddr,
sizeof(ip6h->saddr) +
sizeof(ip6h->daddr),
(const siphash_key_t *)key);
foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
sizeof(ip6h->saddr) +
sizeof(ip6h->daddr),
key));
foc->len = TCP_FASTOPEN_COOKIE_SIZE;
return true;
}
@ -154,7 +153,7 @@ static void tcp_fastopen_cookie_gen(struct sock *sk,
rcu_read_lock();
ctx = tcp_fastopen_get_ctx(sk);
if (ctx)
__tcp_fastopen_cookie_gen_cipher(req, syn, ctx->key[0], foc);
__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
rcu_read_unlock();
}
@ -218,7 +217,7 @@ static int tcp_fastopen_cookie_gen_check(struct sock *sk,
if (!ctx)
goto out;
for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {
__tcp_fastopen_cookie_gen_cipher(req, syn, ctx->key[i], foc);
__tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);
if (tcp_fastopen_cookie_match(foc, orig)) {
ret = i + 1;
goto out;