linux-kernel - [PATCH] ipv6: prevent a possible race condition with lifetimes

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Message-ID: <5599cc3b-8925-4cfd-f035-ae3b87e821a3@ugent.be>
Date:   Sun, 20 Feb 2022 18:54:40 +0100
From:   Niels Dossche <niels.dossche@...nt.be>
To:     "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ipv6: prevent a possible race condition with lifetimes

valid_lft, prefered_lft and tstamp are always accessed under the lock
"lock" in other places. Reading these without taking the lock may result
in inconsistencies regarding the calculation of the valid and preferred
variables since decisions are taken on these fields for those variables.

Signed-off-by: Niels Dossche <niels.dossche@...nt.be>
---
 net/ipv6/addrconf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 3f23da8c0b10..6c8ab3e6e6fe 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4998,6 +4998,7 @@ static int inet6_fill_ifaddr(struct sk_buff *skb, struct inet6_ifaddr *ifa,
            nla_put_s32(skb, IFA_TARGET_NETNSID, args->netnsid))
                goto error;
 
+       spin_lock_bh(&ifa->lock);
        if (!((ifa->flags&IFA_F_PERMANENT) &&
              (ifa->prefered_lft == INFINITY_LIFE_TIME))) {
                preferred = ifa->prefered_lft;
@@ -5019,6 +5020,7 @@ static int inet6_fill_ifaddr(struct sk_buff *skb, struct inet6_ifaddr *ifa,
                preferred = INFINITY_LIFE_TIME;
                valid = INFINITY_LIFE_TIME;
        }
+       spin_unlock_bh(&ifa->lock);
 
        if (!ipv6_addr_any(&ifa->peer_addr)) {
                if (nla_put_in6_addr(skb, IFA_LOCAL, &ifa->addr) < 0 ||
-- 
2.35.1