From: Amit Klein aksecurity@gmail.com
Commit 355b98553789 ("netns: provide pure entropy for net_hash_mix()") makes net_hash_mix() return a true 32 bits of entropy. When used in the IP ID generation algorithm, this has the effect of extending the IP ID generation key from 32 bits to 64 bits.
However, net_hash_mix() is only used for IP ID generation starting with kernel version 4.1. Therefore, earlier kernels remain with 32-bit key no matter what the net_hash_mix() return value is.
This change addresses the issue by explicitly extending the key to 64 bits for kernels older than 4.1.
Signed-off-by: Amit Klein aksecurity@gmail.com Cc: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv4/route.c | 4 +++- net/ipv6/ip6_output.c | 3 +++ 2 files changed, 6 insertions(+), 1 deletion(-)
--- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -488,13 +488,15 @@ EXPORT_SYMBOL(ip_idents_reserve); void __ip_select_ident(struct iphdr *iph, int segs) { static u32 ip_idents_hashrnd __read_mostly; + static u32 ip_idents_hashrnd_extra __read_mostly; u32 hash, id;
net_get_random_once(&ip_idents_hashrnd, sizeof(ip_idents_hashrnd)); + net_get_random_once(&ip_idents_hashrnd_extra, sizeof(ip_idents_hashrnd_extra));
hash = jhash_3words((__force u32)iph->daddr, (__force u32)iph->saddr, - iph->protocol, + iph->protocol ^ ip_idents_hashrnd_extra, ip_idents_hashrnd); id = ip_idents_reserve(hash, segs); iph->id = htons(id); --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -546,12 +546,15 @@ static void ip6_copy_metadata(struct sk_ static void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt) { static u32 ip6_idents_hashrnd __read_mostly; + static u32 ip6_idents_hashrnd_extra __read_mostly; u32 hash, id;
net_get_random_once(&ip6_idents_hashrnd, sizeof(ip6_idents_hashrnd)); + net_get_random_once(&ip6_idents_hashrnd_extra, sizeof(ip6_idents_hashrnd_extra));
hash = __ipv6_addr_jhash(&rt->rt6i_dst.addr, ip6_idents_hashrnd); hash = __ipv6_addr_jhash(&rt->rt6i_src.addr, hash); + hash = jhash_1word(hash, ip6_idents_hashrnd_extra);
id = ip_idents_reserve(hash, 1); fhdr->identification = htonl(id);