inet: fix inet_fill_ifaddr() flags truncation

I missed that (struct ifaddrmsg)->ifa_flags was only 8bits,
while (struct in_ifaddr)->ifa_flags is 32bits.

Use a temporary 32bit variable as I did in set_ifa_lifetime()
and check_lifetime().

Fixes: 3ddc2231c810 ("inet: annotate data-races around ifa->ifa_flags")
Reported-by: Yu Watanabe <watanabe.yu@gmail.com>
Dianosed-by: Yu Watanabe <watanabe.yu@gmail.com>
Closes: https://github.com/systemd/systemd/pull/32666#issuecomment-2103977928
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20240510072932.2678952-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 7a437f0d41905e6acfdc35743afba3a7abfd0dd5..7e45c34c8340a6d2cf96b4485cd4249fd4da7009 100644 (file)
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1683,6 +1683,7 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
        struct nlmsghdr  *nlh;
        unsigned long tstamp;
        u32 preferred, valid;
+       u32 flags;
 
        nlh = nlmsg_put(skb, args->portid, args->seq, args->event, sizeof(*ifm),
                        args->flags);
@@ -1692,7 +1693,13 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
        ifm = nlmsg_data(nlh);
        ifm->ifa_family = AF_INET;
        ifm->ifa_prefixlen = ifa->ifa_prefixlen;
-       ifm->ifa_flags = READ_ONCE(ifa->ifa_flags);
+
+       flags = READ_ONCE(ifa->ifa_flags);
+       /* Warning : ifm->ifa_flags is an __u8, it holds only 8 bits.
+        * The 32bit value is given in IFA_FLAGS attribute.
+        */
+       ifm->ifa_flags = (__u8)flags;
+
        ifm->ifa_scope = ifa->ifa_scope;
        ifm->ifa_index = ifa->ifa_dev->dev->ifindex;
 
@@ -1701,7 +1708,7 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
                goto nla_put_failure;
 
        tstamp = READ_ONCE(ifa->ifa_tstamp);
-       if (!(ifm->ifa_flags & IFA_F_PERMANENT)) {
+       if (!(flags & IFA_F_PERMANENT)) {
                preferred = READ_ONCE(ifa->ifa_preferred_lft);
                valid = READ_ONCE(ifa->ifa_valid_lft);
                if (preferred != INFINITY_LIFE_TIME) {
@@ -1732,7 +1739,7 @@ static int inet_fill_ifaddr(struct sk_buff *skb, const struct in_ifaddr *ifa,
             nla_put_string(skb, IFA_LABEL, ifa->ifa_label)) ||
            (ifa->ifa_proto &&
             nla_put_u8(skb, IFA_PROTO, ifa->ifa_proto)) ||
-           nla_put_u32(skb, IFA_FLAGS, ifm->ifa_flags) ||
+           nla_put_u32(skb, IFA_FLAGS, flags) ||
            (ifa->ifa_rt_priority &&
             nla_put_u32(skb, IFA_RT_PRIORITY, ifa->ifa_rt_priority)) ||
            put_cacheinfo(skb, READ_ONCE(ifa->ifa_cstamp), tstamp,