net: fastopen: robustness and endianness fixes for SipHash

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.

Ard Biesheuvel committed 7 years ago

Commit 438ac881 parent 92ad6325 files · +24 −27Browse files

Unified · Split

5 files

include/linux/tcp.h +1 −1
include/net/tcp.h +4 −4
net/ipv4/sysctl_net_ipv4.c +1 −2
net/ipv4/tcp.c +1 −2
net/ipv4/tcp_fastopen.c +17 −18

include/linux/tcp.h+1−1

@@ -58,7 +58,7 @@ static inline unsigned int tcp_optlen(const struct sk_buff *skb) · 57 unmodified lines
58	58
59	59	/* TCP Fast Open Cookie as stored in memory */
60	60	struct tcp_fastopen_cookie {
61		− u64 val[TCP_FASTOPEN_COOKIE_MAX / sizeof(u64)];
	61	+ __le64 val[DIV_ROUND_UP(TCP_FASTOPEN_COOKIE_MAX, sizeof(u64))];
62	62	s8 len;
63	63	bool exp; /* In RFC6994 experimental option format */
64	64	};

include/net/tcp.h+4−4

@@ -43,6 +43,7 @@ · 42 unmodified lines
43	43	#include <linux/seq_file.h>
44	44	#include <linux/memcontrol.h>
45	45	#include <linux/bpf-cgroup.h>
	46	+#include <linux/siphash.h>
46	47
47	48	extern struct inet_hashinfo tcp_hashinfo;
48	49
@@ -1612,8 +1613,7 @@ void tcp_free_fastopen_req(struct tcp_sock *tp); · 1563 unmodified lines
1612	1613	void tcp_fastopen_destroy_cipher(struct sock *sk);
1613	1614	void tcp_fastopen_ctx_destroy(struct net *net);
1614	1615	int tcp_fastopen_reset_cipher(struct net net, struct sock sk,
1615		− void primary_key, void backup_key,
1616		− unsigned int len);
	1616	+ void primary_key, void backup_key);
1617	1617	void tcp_fastopen_add_skb(struct sock sk, struct sk_buff skb);
1618	1618	struct sock tcp_try_fastopen(struct sock sk, struct sk_buff *skb,
1619	1619	struct request_sock *req,
@@ -1623,14 +1623,14 @@ void tcp_fastopen_init_key_once(struct net *net); · 3 unmodified lines
1623	1623	bool tcp_fastopen_cookie_check(struct sock sk, u16 mss,
1624	1624	struct tcp_fastopen_cookie *cookie);
1625	1625	bool tcp_fastopen_defer_connect(struct sock sk, int err);
1626		−#define TCP_FASTOPEN_KEY_LENGTH 16
	1626	+#define TCP_FASTOPEN_KEY_LENGTH sizeof(siphash_key_t)
1627	1627	#define TCP_FASTOPEN_KEY_MAX 2
1628	1628	#define TCP_FASTOPEN_KEY_BUF_LENGTH \
1629	1629	(TCP_FASTOPEN_KEY_LENGTH * TCP_FASTOPEN_KEY_MAX)
1630	1630
1631	1631	/* Fastopen key context */
1632	1632	struct tcp_fastopen_context {
1633		− __u8 key[TCP_FASTOPEN_KEY_MAX][TCP_FASTOPEN_KEY_LENGTH];
	1633	+ siphash_key_t key[TCP_FASTOPEN_KEY_MAX];
1634	1634	int num;
1635	1635	struct rcu_head rcu;
1636	1636	};

net/ipv4/sysctl_net_ipv4.c+1−2

@@ -365,8 +365,7 @@ static int proc_tcp_fastopen_key(struct ctl_table *table, int write, · 364 unmodified lines
365	365	}
366	366	}
367	367	tcp_fastopen_reset_cipher(net, NULL, key,
368		− backup_data ? key + 4 : NULL,
369		− TCP_FASTOPEN_KEY_LENGTH);
	368	+ backup_data ? key + 4 : NULL);
370	369	}
371	370
372	371	bad_key:

net/ipv4/tcp.c+1−2

@@ -2822,8 +2822,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level, · 2821 unmodified lines
2822	2822	if (optlen == TCP_FASTOPEN_KEY_BUF_LENGTH)
2823	2823	backup_key = key + TCP_FASTOPEN_KEY_LENGTH;
2824	2824
2825		− return tcp_fastopen_reset_cipher(net, sk, key, backup_key,
2826		− TCP_FASTOPEN_KEY_LENGTH);
	2825	+ return tcp_fastopen_reset_cipher(net, sk, key, backup_key);
2827	2826	}
2828	2827	default:
2829	2828	/* fallthru */

net/ipv4/tcp_fastopen.c+17−18

@@ -7,7 +7,6 @@ · 6 unmodified lines
7	7	#include <linux/tcp.h>
8	8	#include <linux/rcupdate.h>
9	9	#include <linux/rculist.h>
10		−#include <linux/siphash.h>
11	10	#include <net/inetpeer.h>
12	11	#include <net/tcp.h>
13	12
@@ -31,7 +30,7 @@ void tcp_fastopen_init_key_once(struct net *net) · 17 unmodified lines
31	30	* for a valid cookie, so this is an acceptable risk.
32	31	*/
33	32	get_random_bytes(key, sizeof(key));
34		− tcp_fastopen_reset_cipher(net, NULL, key, NULL, sizeof(key));
	33	+ tcp_fastopen_reset_cipher(net, NULL, key, NULL);
35	34	}
36	35
37	36	static void tcp_fastopen_ctx_free(struct rcu_head *head)
@@ -68,8 +67,7 @@ void tcp_fastopen_ctx_destroy(struct net *net) · 30 unmodified lines
68	67	}
69	68
70	69	int tcp_fastopen_reset_cipher(struct net net, struct sock sk,
71		− void primary_key, void backup_key,
72		− unsigned int len)
	70	+ void primary_key, void backup_key)
73	71	{
74	72	struct tcp_fastopen_context ctx, octx;
75	73	struct fastopen_queue *q;
@@ -81,9 +79,11 @@ int tcp_fastopen_reset_cipher(struct net net, struct sock sk, · 5 unmodified lines
81	79	goto out;
82	80	}
83	81
84		− memcpy(ctx->key[0], primary_key, len);
	82	+ ctx->key[0].key[0] = get_unaligned_le64(primary_key);
	83	+ ctx->key[0].key[1] = get_unaligned_le64(primary_key + 8);
85	84	if (backup_key) {
86		− memcpy(ctx->key[1], backup_key, len);
	85	+ ctx->key[1].key[0] = get_unaligned_le64(backup_key);
	86	+ ctx->key[1].key[1] = get_unaligned_le64(backup_key + 8);
87	87	ctx->num = 2;
88	88	} else {
89	89	ctx->num = 1;
@@ -110,19 +110,18 @@ out: · 20 unmodified lines
110	110
111	111	static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req,
112	112	struct sk_buff *syn,
113		− const u8 *key,
	113	+ const siphash_key_t *key,
114	114	struct tcp_fastopen_cookie *foc)
115	115	{
116		− BUILD_BUG_ON(TCP_FASTOPEN_KEY_LENGTH != sizeof(siphash_key_t));
117	116	BUILD_BUG_ON(TCP_FASTOPEN_COOKIE_SIZE != sizeof(u64));
118	117
119	118	if (req->rsk_ops->family == AF_INET) {
120	119	const struct iphdr *iph = ip_hdr(syn);
121	120
122		− foc->val[0] = siphash(&iph->saddr,
123		− sizeof(iph->saddr) +
124		− sizeof(iph->daddr),
125		− (const siphash_key_t *)key);
	121	+ foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
	122	+ sizeof(iph->saddr) +
	123	+ sizeof(iph->daddr),
	124	+ key));
126	125	foc->len = TCP_FASTOPEN_COOKIE_SIZE;
127	126	return true;
128	127	}
@@ -130,10 +129,10 @@ static bool __tcp_fastopen_cookie_gen_cipher(struct request_sock *req, · 1 unmodified line
130	129	if (req->rsk_ops->family == AF_INET6) {
131	130	const struct ipv6hdr *ip6h = ipv6_hdr(syn);
132	131
133		− foc->val[0] = siphash(&ip6h->saddr,
134		− sizeof(ip6h->saddr) +
135		− sizeof(ip6h->daddr),
136		− (const siphash_key_t *)key);
	132	+ foc->val[0] = cpu_to_le64(siphash(&ip6h->saddr,
	133	+ sizeof(ip6h->saddr) +
	134	+ sizeof(ip6h->daddr),
	135	+ key));
137	136	foc->len = TCP_FASTOPEN_COOKIE_SIZE;
138	137	return true;
139	138	}
@@ -154,7 +153,7 @@ static void tcp_fastopen_cookie_gen(struct sock *sk, · 14 unmodified lines
154	153	rcu_read_lock();
155	154	ctx = tcp_fastopen_get_ctx(sk);
156	155	if (ctx)
157		− __tcp_fastopen_cookie_gen_cipher(req, syn, ctx->key[0], foc);
	156	+ __tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
158	157	rcu_read_unlock();
159	158	}
160	159
@@ -218,7 +217,7 @@ static int tcp_fastopen_cookie_gen_check(struct sock *sk, · 57 unmodified lines
218	217	if (!ctx)
219	218	goto out;
220	219	for (i = 0; i < tcp_fastopen_context_len(ctx); i++) {
221		− __tcp_fastopen_cookie_gen_cipher(req, syn, ctx->key[i], foc);
	220	+ __tcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[i], foc);
222	221	if (tcp_fastopen_cookie_match(foc, orig)) {
223	222	ret = i + 1;
224	223	goto out;

net: fastopen: robustness and endianness fixes for SipHash

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