Re: [net PATCH v2 2/2] net: netprio: fd passed in SCM_RIGHTS datagram not set correctly

A socket fd passed in a SCM_RIGHTS datagram was not getting
updated with the new tasks cgrp prioidx. This leaves IO on
the socket tagged with the old tasks priority.

To fix this add a check in the scm recvmsg path to update the
sock cgrp prioidx with the new tasks value.

Thanks to Al Viro for catching this.

CC: Neil Horman <nhorman@tuxdriver.com>
Reported-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: John Fastabend <redacted>
---

 net/core/scm.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/net/core/scm.c b/net/core/scm.c
index 8f6ccfd..a14d9e2 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c

@@ -249,6 +249,7 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 	struct file **fp = scm->fp->fp;
 	int __user *cmfptr;
 	int err = 0, i;
+	__u32 prioidx = task_netprioidx(current);
 
 	if (MSG_CMSG_COMPAT & msg->msg_flags) {
 		scm_detach_fds_compat(msg, scm);

@@ -265,6 +266,7 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 	for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 	     i++, cmfptr++)
 	{
+		struct socket *sock;
 		int new_fd;
 		err = security_file_receive(fp[i]);
 		if (err)

@@ -281,6 +283,9 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 		}
 		/* Bump the usage count and install the file. */
 		get_file(fp[i]);
+		sock = sock_from_file(fp[i], &err);
+		if (sock)
+			sock->sk->sk_cgrp_prioidx = prioidx;