| Message ID | 1406357890.12728.9.camel@edumazet-glaptop2.roam.corp.google.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Sat, 26 Jul 2014 08:58:10 +0200 > From: Eric Dumazet <edumazet@google.com> > > In "Counting Packets Sent Between Arbitrary Internet Hosts", Jeffrey and > Jedidiah describe ways exploiting linux IP identifier generation to > infer whether two machines are exchanging packets. > > With commit 73f156a6e8c1 ("inetpeer: get rid of ip_id_count"), we > changed IP id generation, but this does not really prevent this > side-channel technique. > > This patch adds a random amount of perturbation so that IP identifiers > for a given destination [1] are no longer monotonically increasing after > an idle period. > > Note that prandom_u32_max(1) returns 0, so if generator is used at most > once per jiffy, this patch inserts no hole in the ID suite and do not > increase collision probability. > > This is jiffies based, so in the worst case (HZ=1000), the id can > rollover after ~65 seconds of idle time, which should be fine. > > We also change the hash used in __ip_select_ident() to not only hash > on daddr, but also saddr and protocol, so that ICMP probes can not be > used to infer information for other protocols. > > For IPv6, adds saddr into the hash as well, but not nexthdr. > > If I ping the patched target, we can see ID are now hard to predict. ... > [1] TCP sessions uses a per flow ID generator not changed by this patch. > > Signed-off-by: Eric Dumazet <edumazet@google.com> > Reported-by: Jeffrey Knockel <jeffk@cs.unm.edu> > Reported-by: Jedidiah R. Crandall <crandall@cs.unm.edu> Applied and queued up for -stable, thanks everyone. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/net/ip.h b/include/net/ip.h index 0e795df05ec9..7596eb22e1ce 100644 --- a/include/net/ip.h +++ b/include/net/ip.h @@ -309,16 +309,7 @@ static inline unsigned int ip_skb_dst_mtu(const struct sk_buff *skb) } } -#define IP_IDENTS_SZ 2048u -extern atomic_t *ip_idents; - -static inline u32 ip_idents_reserve(u32 hash, int segs) -{ - atomic_t *id_ptr = ip_idents + hash % IP_IDENTS_SZ; - - return atomic_add_return(segs, id_ptr) - segs; -} - +u32 ip_idents_reserve(u32 hash, int segs); void __ip_select_ident(struct iphdr *iph, int segs); static inline void ip_select_ident_segs(struct sk_buff *skb, struct sock *sk, int segs) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 3162ea923ded..190199851c9a 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -457,8 +457,31 @@ static struct neighbour *ipv4_neigh_lookup(const struct dst_entry *dst, return neigh_create(&arp_tbl, pkey, dev); } -atomic_t *ip_idents __read_mostly; -EXPORT_SYMBOL(ip_idents); +#define IP_IDENTS_SZ 2048u +struct ip_ident_bucket { + atomic_t id; + u32 stamp32; +}; + +static struct ip_ident_bucket *ip_idents __read_mostly; + +/* In order to protect privacy, we add a perturbation to identifiers + * if one generator is seldom used. This makes hard for an attacker + * to infer how many packets were sent between two points in time. + */ +u32 ip_idents_reserve(u32 hash, int segs) +{ + struct ip_ident_bucket *bucket = ip_idents + hash % IP_IDENTS_SZ; + u32 old = ACCESS_ONCE(bucket->stamp32); + u32 now = (u32)jiffies; + u32 delta = 0; + + if (old != now && cmpxchg(&bucket->stamp32, old, now) == old) + delta = prandom_u32_max(now - old); + + return atomic_add_return(segs + delta, &bucket->id) - segs; +} +EXPORT_SYMBOL(ip_idents_reserve); void __ip_select_ident(struct iphdr *iph, int segs) { @@ -467,7 +490,10 @@ void __ip_select_ident(struct iphdr *iph, int segs) net_get_random_once(&ip_idents_hashrnd, sizeof(ip_idents_hashrnd)); - hash = jhash_1word((__force u32)iph->daddr, ip_idents_hashrnd); + hash = jhash_3words((__force u32)iph->daddr, + (__force u32)iph->saddr, + iph->protocol, + ip_idents_hashrnd); id = ip_idents_reserve(hash, segs); iph->id = htons(id); } diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index cb9df0eb4023..45702b8cd141 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -545,6 +545,8 @@ static void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt) net_get_random_once(&ip6_idents_hashrnd, sizeof(ip6_idents_hashrnd)); hash = __ipv6_addr_jhash(&rt->rt6i_dst.addr, ip6_idents_hashrnd); + hash = __ipv6_addr_jhash(&rt->rt6i_src.addr, hash); + id = ip_idents_reserve(hash, 1); fhdr->identification = htonl(id); }