[PATCH 4.20 010/127] netlink: fixup regression in RTM_GETADDR

[Greg Kroah-Hartman]

4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Arthur Gautier <baloo@xxxxxxxxx>

[ Upstream commit 7c1e8a3817c55d73b27cc29b84075999c8894179 ]

This commit fixes a regression in AF_INET/RTM_GETADDR and
AF_INET6/RTM_GETADDR.

Before this commit, the kernel would stop dumping addresses once the first
skb was full and end the stream with NLMSG_DONE(-EMSGSIZE). The error
shouldn't be sent back to netlink_dump so the callback is kept alive. The
userspace is expected to call back with a new empty skb.

Changes from V1:
 - The error is not handled in netlink_dump anymore but rather in
   inet_dump_ifaddr and inet6_dump_addr directly as suggested by
   David Ahern.

Fixes: d7e38611b81e ("net/ipv4: Put target net when address dump fails due to bad attributes")
Fixes: 242afaa6968c ("net/ipv6: Put target net when address dump fails due to bad attributes")

Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: "David S . Miller" <davem@xxxxxxxxxxxxx>
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Arthur Gautier <baloo@xxxxxxxxx>
Reviewed-by: David Ahern <dsahern@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/ipv4/devinet.c  |    2 +-
 net/ipv6/addrconf.c |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1826,7 +1826,7 @@ put_tgt_net:
 	if (fillargs.netnsid >= 0)
 		put_net(tgt_net);
 
-	return err < 0 ? err : skb->len;
+	return skb->len ? : err;
 }
 
 static void rtmsg_ifa(int event, struct in_ifaddr *ifa, struct nlmsghdr *nlh,
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -5154,7 +5154,7 @@ put_tgt_net:
 	if (fillargs.netnsid >= 0)
 		put_net(tgt_net);
 
-	return err < 0 ? err : skb->len;
+	return skb->len ? : err;
 }
 
 static int inet6_dump_ifaddr(struct sk_buff *skb, struct netlink_callback *cb)