Re: Problem with patch "make nlmsg_end() and genlmsg_end() void"

[Marcel Holtmann <marcel@holtmann.org>]

Hi Johannes,

> your commit 053c095a82cf773075e83d7233b5cc19a1f73ece is causing problems with systemd-networkd.
> 
> I have an up-to-date Arch Linux installation in a KVM and your change causes massive problems. It makes systemd-networkd to run out of memory.
> 
> systemd-fsck[84]: /dev/vda1: clean, 53283/131072 files, 409813/524032 blocks
> Out of memory: Kill process 142 (systemd-network) score 923 or sacrifice child
> Killed process 142 (systemd-network) total-vm:478416kB, anon-rss:463472kB, file-rss:460kB
> [FAILED] Failed to start Network Service.
> See "systemctl status systemd-networkd.service" for details.
>         Stopping Network Service...
> [  OK  ] Stopped Network Service.
>         Starting Network Service...
> 
> Arch Linux 3.19.0-rc4-devel+ (ttyS0)
> 
> marcel login: Out of memory: Kill process 154 (systemd-network) score 932 or sacrifice child
> Killed process 154 (systemd-network) total-vm:540784kB, anon-rss:468380kB, file-rss:132kB
> Out of memory: Kill process 158 (systemd-network) score 932 or sacrifice child
> Killed process 158 (systemd-network) total-vm:540388kB, anon-rss:468528kB, file-rss:48kB
> Out of memory: Kill process 160 (systemd-network) score 932 or sacrifice child
> Killed process 160 (systemd-network) total-vm:540916kB, anon-rss:468528kB, file-rss:4kB
> Out of memory: Kill process 162 (systemd-network) score 931 or sacrifice child
> Killed process 162 (systemd-network) total-vm:540916kB, anon-rss:468104kB, file-rss:76kB

so this was freaking nasty to find since I had to dig into every single RTNL location that might have an affect on this. I think that I tracked this down to these two locations:

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index e13b9dbdf154..0e26b9f66cad 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1327,7 +1327,7 @@ static int rtnl_dump_ifinfo(struct sk_buff *skb, struct netlink_callback *cb)
                         */
                        WARN_ON((err == -EMSGSIZE) && (skb->len == 0));
 
-                       if (err <= 0)
+                       if (err < 0)
                                goto out;
 
                        nl_dump_check_consistent(cb, nlmsg_hdr(skb));
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 8975d9501d50..d6b4f5d08014 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4213,7 +4213,7 @@ static int inet6_dump_addr(struct sk_buff *skb, struct netlink_callback *cb,
                                goto cont;
 
                        if (in6_dump_addrs(idev, skb, cb, type,
-                                          s_ip_idx, &ip_idx) <= 0)
+                                          s_ip_idx, &ip_idx) < 0)
                                goto done;
 cont:
                        idx++;

However I am not sure that these are the only ones. We might have additional issues in functionality that systemd-networkd actually does not use at the moment. These two changes make my KVM image boot properly again.

And actually I am not even sure that these two changes are correct. My KVM image is a dead simple image with no IPv6 support. This change might actually just broke IPv6 and I would not notice.

Tom, do you know if we can do anything in systemd-networkd in regards to RTNL and netlink handling to throw a big warning when something comes back from the kernel that would cause massive memory allocation.

Regards

Marcel