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udp: In udp_flow_src_port use random hash value if skb_get_hash fails

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In the unlikely event that skb_get_hash is unable to deduce a hash
in udp_flow_src_port we use a consistent random value instead.
This is specified in GRE/UDP draft section 3.2.1:
https://tools.ietf.org/html/draft-ietf-tsvwg-gre-in-udp-encap-04

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tom Herbert 2015-02-24 09:17:31 -08:00 • committed by David S. Miller
parent fed0a159c8
commit 723b8e460d
2 changed files with 25 additions and 6 deletions
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21
include/net/udp.h
View file

@ -194,6 +194,8 @@ int udp_lib_get_port(struct sock *sk, unsigned short snum,
int (*)(const struct sock *, const struct sock *), int (*)(const struct sock *, const struct sock *),
unsigned int hash2_nulladdr); unsigned int hash2_nulladdr);
u32 udp_flow_hashrnd(void);
static inline __be16 udp_flow_src_port(struct net *net, struct sk_buff *skb, static inline __be16 udp_flow_src_port(struct net *net, struct sk_buff *skb,
int min, int max, bool use_eth) int min, int max, bool use_eth)
{ {
@ -205,12 +207,19 @@ static inline __be16 udp_flow_src_port(struct net *net, struct sk_buff *skb,
} }
hash = skb_get_hash(skb); hash = skb_get_hash(skb);
if (unlikely(!hash) && use_eth) { if (unlikely(!hash)) {
/* Can't find a normal hash, caller has indicated an Ethernet if (use_eth) {
* packet so use that to compute a hash. /* Can't find a normal hash, caller has indicated an
*/ * Ethernet packet so use that to compute a hash.
hash = jhash(skb->data, 2 * ETH_ALEN, */
(__force u32) skb->protocol); hash = jhash(skb->data, 2 * ETH_ALEN,
(__force u32) skb->protocol);
} else {
/* Can't derive any sort of hash for the packet, set
* to some consistent random value.
*/
hash = udp_flow_hashrnd();
}
} }
/* Since this is being sent on the wire obfuscate hash a bit /* Since this is being sent on the wire obfuscate hash a bit

10
net/ipv4/udp.c
View file

@ -2525,6 +2525,16 @@ void __init udp_table_init(struct udp_table *table, const char *name)
} }
} }
u32 udp_flow_hashrnd(void)
{
static u32 hashrnd __read_mostly;
net_get_random_once(&hashrnd, sizeof(hashrnd));
return hashrnd;
}
EXPORT_SYMBOL(udp_flow_hashrnd);
void __init udp_init(void) void __init udp_init(void)
{ {
unsigned long limit; unsigned long limit;