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Date: Wed, 30 May 2018 15:45:29 +0300
From: Timo Teras <timo.teras@....fi>
To: Matej Kupljen <matej.kupljen@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: Endless loop in netlink_msg_to_ifaddr
On Wed, 30 May 2018 11:57:03 +0200
Matej Kupljen <matej.kupljen@...il.com> wrote:
> I am using OpenWRT device with MUSL C library version 1.1.19 and I am
> running custom binary on it. I noticed that during testing my program
> started using 99% CPU.
> I build OpenWRT myself so I have all the sources. I attached the
> gdbserver and checked what is going on.
Thanks for the report!
> As you can see the first message in netlink reply has a rta_len set
> to zero so the list is never traversed, only the first message is
> received every time.
>
> I am not sure if this is the correct response from netlink, however
> the program is stucked here.
>
> Any ideas?
> Please CC me in reply.
That is invalid message to my understanding. Perhaps there's some new
extensions that allow it. Upstream (linux kernel) RTA_OK does do
additional checks against this situation.
The same issue probably affects if_nameindex.
I think the following should fix it:
diff --git a/src/network/netlink.h b/src/network/netlink.h
index 20700ac5..00dc7172 100644
--- a/src/network/netlink.h
+++ b/src/network/netlink.h
@@ -80,13 +80,13 @@ struct ifaddrmsg {
#define NLMSG_DATALEN(nlh) ((nlh)->nlmsg_len-sizeof(struct nlmsghdr))
#define NLMSG_DATAEND(nlh) ((char*)(nlh)+(nlh)->nlmsg_len)
#define NLMSG_NEXT(nlh) (struct nlmsghdr*)((char*)(nlh)+NETLINK_ALIGN((nlh)->nlmsg_len))
-#define NLMSG_OK(nlh,end) ((char*)(end)-(char*)(nlh) >= sizeof(struct nlmsghdr))
+#define NLMSG_OK(nlh,end) ((char*)(end)-(char*)(nlh) >= sizeof(struct nlmsghdr) && (nlh)->nlmsg_len >= sizeof(struct nlmsghdr))
#define RTA_DATA(rta) ((void*)((char*)(rta)+sizeof(struct rtattr)))
#define RTA_DATALEN(rta) ((rta)->rta_len-sizeof(struct rtattr))
#define RTA_DATAEND(rta) ((char*)(rta)+(rta)->rta_len)
#define RTA_NEXT(rta) (struct rtattr*)((char*)(rta)+NETLINK_ALIGN((rta)->rta_len))
-#define RTA_OK(nlh,end) ((char*)(end)-(char*)(rta) >= sizeof(struct rtattr))
+#define RTA_OK(rta,end) ((char*)(end)-(char*)(rta) >= sizeof(struct rtattr) && (rta)->rta_len >= sizeof(struct rtattr))
#define NLMSG_RTA(nlh,len) ((void*)((char*)(nlh)+sizeof(struct nlmsghdr)+NETLINK_ALIGN(len)))
#define NLMSG_RTAOK(rta,nlh) RTA_OK(rta,NLMSG_DATAEND(nlh))
Could you try if this fixes it?
You will probably need to 'make clean' or at least force recompilation
of src/network/{getifaddrs,if_nameindex,netlink}.c as the netlink.h
dependency is not picked up by the makefile automatically.
@dalias, if the above looks good to you, I am happy to submit properly
formatted git patch for it.
Thanks,
Timo
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