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ipmonitor: Fix recvmsg with ancillary data 

A successful call to recvmsg() causes msg.msg_controllen to contain the length
of the received ancillary data. However, the current code in the 'ip' utility
doesn't reset this value after each recvmsg().

This means that if a call to recvmsg() doesn't have ancillary data, then
'msg.msg_controllen' will be set to 0, causing future recvmsg() which do
contain ancillary data to get MSG_CTRUNC set in msg.msg_flags.

This fixes 'ip monitor' running with the all-nsid option - With this option the
kernel passes the nsid as ancillary data. If while 'ip monitor' is running an
even on the current netns is received, then no ancillary data will be sent,
causing 'msg.msg_controllen' to be set to 0, which causes 'ip monitor' to
indefinitely print "[nsid current]" instead of the real nsid.

Fixes: 449b824ad1 ("ipmonitor: allows to monitor in several netns")
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Lahav Schlesinger <lschlesinger@drivenets.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
This commit is contained in:
Lahav Schlesinger 2021-07-15 17:38:56 +03:00 committed by Stephen Hemminger
parent 7a7e9ed98f
commit f760bff328
1 changed files with 5 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
lib/libnetlink.c
View File

@ -1175,16 +1175,16 @@ int rtnl_listen(struct rtnl_handle *rtnl,
char buf[16384]; char buf[16384];
char cmsgbuf[BUFSIZ]; char cmsgbuf[BUFSIZ];
if (rtnl->flags & RTNL_HANDLE_F_LISTEN_ALL_NSID) {
msg.msg_control = &cmsgbuf;
msg.msg_controllen = sizeof(cmsgbuf);
}
iov.iov_base = buf; iov.iov_base = buf;
while (1) { while (1) {
struct rtnl_ctrl_data ctrl; struct rtnl_ctrl_data ctrl;
struct cmsghdr *cmsg; struct cmsghdr *cmsg;
if (rtnl->flags & RTNL_HANDLE_F_LISTEN_ALL_NSID) {
msg.msg_control = &cmsgbuf;
msg.msg_controllen = sizeof(cmsgbuf);
}
iov.iov_len = sizeof(buf); iov.iov_len = sizeof(buf);
status = recvmsg(rtnl->fd, &msg, 0); status = recvmsg(rtnl->fd, &msg, 0);