Re: [LARTC] Adding dsmark qdisc fails

[Thomas Graf <tgraf@suug.ch>]

* Patrick McHardy <423D9398.8050907@trash.net> 2005-03-20 16:15
> ># tc qdisc add dev eth1 handle 1:0 root dsmark indices 8
> >RTNETLINK answers: Invalid argument
> >Mar 20 13:00:50 user user.debug kernel: dsmark_init(sch a0bb3ae0,[qdisc 
> >a0bb3b60],opt 00000000)
> >
> It is caused by this patch, the transformation to use NLMSG_TAIL is
> not equivalent (it calculates the size of the aligned message). This
> makes parsing the attributes in rtnetlink_rcv_msg() fail. I haven't 
> checked what the exact problem is, Thomas, can you have a look at this
> please?

My patch is right but discovered a quite more serious bug in the
generic routing attribute handling. nlmsg_len is not aligned to
RTA_ALIGNTO if the data length of the attribute did not have
this alignment itself. The fact that the addition of the next attribute
fixed this bug automatically by issueing NLMSG_ALIGN(nlmsg_len) + len
put a good shadow around it and made it only a problem when the last
attribute added was not properly aligned. Patch attached, alternatively
one can clone bk://kernel.bkbits.net/tgraf/iproute2-tgr and als get
the new fancy multipath bits installed. ;->

# This is a BitKeeper generated diff -Nru style patch.
#
# ChangeSet
#   2005/03/20 17:19:39+01:00 tgraf@suug.ch 
#   Fix netlink message alignment when the last routing attribute added
#   has a data length not aligned to RTA_ALIGNTO.
# 
# lib/libnetlink.c
#   2005/03/20 17:19:38+01:00 tgraf@suug.ch +4 -4
#   Fix netlink message alignment when the last routing attribute added
#   has a data length not aligned to RTA_ALIGNTO.
# 
diff -Nru a/lib/libnetlink.c b/lib/libnetlink.c
--- a/lib/libnetlink.c	2005-03-20 17:19:53 +01:00
+++ b/lib/libnetlink.c	2005-03-20 17:19:53 +01:00
@@ -491,7 +491,7 @@
 	int len = RTA_LENGTH(alen);
 	struct rtattr *rta;
 
-	if (NLMSG_ALIGN(n->nlmsg_len) + len > maxlen) {
+	if (NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(len) > maxlen) {
 		fprintf(stderr, "addattr_l ERROR: message exceeded bound of %d\n",maxlen);
 		return -1;
 	}
@@ -499,7 +499,7 @@
 	rta->rta_type = type;
 	rta->rta_len = len;
 	memcpy(RTA_DATA(rta), data, alen);
-	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + len;
+	n->nlmsg_len = NLMSG_ALIGN(n->nlmsg_len) + RTA_ALIGN(len);
 	return 0;
 }
 
@@ -539,7 +539,7 @@
 	struct rtattr *subrta;
 	int len = RTA_LENGTH(alen);
 
-	if (RTA_ALIGN(rta->rta_len) + len > maxlen) {
+	if (RTA_ALIGN(rta->rta_len) + RTA_ALIGN(len) > maxlen) {
 		fprintf(stderr,"rta_addattr_l: Error! max allowed bound %d exceeded\n",maxlen);
 		return -1;
 	}
@@ -547,7 +547,7 @@
 	subrta->rta_type = type;
 	subrta->rta_len = len;
 	memcpy(RTA_DATA(subrta), data, alen);
-	rta->rta_len = NLMSG_ALIGN(rta->rta_len) + len;
+	rta->rta_len = NLMSG_ALIGN(rta->rta_len) + RTA_ALIGN(len);
 	return 0;
 }
 
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