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Commit 39c36094 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

net: fix inet_getid() and ipv6_select_ident() bugs 



I noticed we were sending wrong IPv4 ID in TCP flows when MTU discovery
is disabled.
Note how GSO/TSO packets do not have monotonically incrementing ID.

06:37:41.575531 IP (id 14227, proto: TCP (6), length: 4396)
06:37:41.575534 IP (id 14272, proto: TCP (6), length: 65212)
06:37:41.575544 IP (id 14312, proto: TCP (6), length: 57972)
06:37:41.575678 IP (id 14317, proto: TCP (6), length: 7292)
06:37:41.575683 IP (id 14361, proto: TCP (6), length: 63764)

It appears I introduced this bug in linux-3.1.

inet_getid() must return the old value of peer->ip_id_count,
not the new one.

Lets revert this part, and remove the prevention of
a null identification field in IPv6 Fragment Extension Header,
which is dubious and not even done properly.

Fixes: 87c48fa3 ("ipv6: make fragment identifications less predictable")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fc0d6e9c

include/net/inetpeer.h

+1 −8
Original line number Diff line number Diff line
@@ -177,16 +177,9 @@ static inline void inet_peer_refcheck(const struct inet_peer *p) 
/* can be called with or without local BH being disabled */

static inline int inet_getid(struct inet_peer *p, int more)

{

	int old, new;

	more++;

	inet_peer_refcheck(p);

	do {

		old = atomic_read(&p->ip_id_count);

		new = old + more;

		if (!new)

			new = 1;

	} while (atomic_cmpxchg(&p->ip_id_count, old, new) != old);

	return new;

	return atomic_add_return(more, &p->ip_id_count) - more;

}



#endif /* _NET_INETPEER_H */

net/ipv6/output_core.c

+3 −8
Original line number Diff line number Diff line
@@ -12,7 +12,7 @@ void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt) 
{

	static atomic_t ipv6_fragmentation_id;

	struct in6_addr addr;

	int old, new;

	int ident;



#if IS_ENABLED(CONFIG_IPV6)

	struct inet_peer *peer;
@@ -26,15 +26,10 @@ void ipv6_select_ident(struct frag_hdr *fhdr, struct rt6_info *rt) 
		return;

	}

#endif

	do {

		old = atomic_read(&ipv6_fragmentation_id);

		new = old + 1;

		if (!new)

			new = 1;

	} while (atomic_cmpxchg(&ipv6_fragmentation_id, old, new) != old);

	ident = atomic_inc_return(&ipv6_fragmentation_id);



	addr = rt->rt6i_dst.addr;

	addr.s6_addr32[0] ^= (__force __be32)new;

	addr.s6_addr32[0] ^= (__force __be32)ident;

	fhdr->identification = htonl(secure_ipv6_id(addr.s6_addr32));

}

EXPORT_SYMBOL(ipv6_select_ident);