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net: fix __dst_negative_advice() race

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__dst_negative_advice() does not enforce proper RCU rules when
sk->dst_cache must be cleared, leading to possible UAF.

RCU rules are that we must first clear sk->sk_dst_cache,
then call dst_release(old_dst).

Note that sk_dst_reset(sk) is implementing this protocol correctly,
while __dst_negative_advice() uses the wrong order.

Given that ip6_negative_advice() has special logic
against RTF_CACHE, this means each of the three ->negative_advice()
existing methods must perform the sk_dst_reset() themselves.

Note the check against NULL dst is centralized in
__dst_negative_advice(), there is no need to duplicate
it in various callbacks.

Many thanks to Clement Lecigne for tracking this issue.

This old bug became visible after the blamed commit, using UDP sockets.

Fixes: a87cb3e48e ("net: Facility to report route quality of connected sockets")
Reported-by: Clement Lecigne <clecigne@google.com>
Diagnosed-by: Clement Lecigne <clecigne@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <tom@herbertland.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240528114353.1794151-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet
2024-05-28 11:43:53 +00:00
committed by Jakub Kicinski
parent 068648aab7
commit 92f1655aa2
5 changed files with 30 additions and 47 deletions
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11
net/xfrm/xfrm_policy.c
View File

@ -3910,15 +3910,10 @@ static void xfrm_link_failure(struct sk_buff *skb)
/* Impossible. Such dst must be popped before reaches point of failure. */
}
static struct dst_entry *xfrm_negative_advice(struct dst_entry *dst)
static void xfrm_negative_advice(struct sock *sk, struct dst_entry *dst)
{
if (dst) {
if (dst->obsolete) {
dst_release(dst);
dst = NULL;
}
}
return dst;
if (dst->obsolete)
sk_dst_reset(sk);
}
static void xfrm_init_pmtu(struct xfrm_dst **bundle, int nr)