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: 3ddc223 ("inet: annotate data-races around ifa->ifa_flags")
Reported-by: Yu Watanabe <[email protected]>
Dianosed-by: Yu Watanabe <[email protected]>
Closes: systemd/systemd#32666 (comment)
Signed-off-by: Eric Dumazet <[email protected]>
Reviewed-by: Larysa Zaremba <[email protected]>
Reviewed-by: David Ahern <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Eric Dumazet

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,