[net PATCH v1 1/2] net: netprio: fix files lock and remove useless d_path bits

Add lock to prevent a race with a file closing and also remove
useless and ugly sscanf code. The extra code was never needed
and the case it supposedly protected against is in fact handled
correctly by sock_from_file as pointed out by Al Viro.

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

 net/core/netprio_cgroup.c |   15 ++++-----------
 1 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c
index ed0c043..0323ec3 100644
--- a/net/core/netprio_cgroup.c
+++ b/net/core/netprio_cgroup.c

@@ -296,29 +296,22 @@ void net_prio_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
 			continue;
 		}
 
-		rcu_read_lock();
+		spin_lock(&files->file_lock);
 		fdt = files_fdtable(files);
 		for (fd = 0; fd < fdt->max_fds; fd++) {
-			char *path;
 			struct file *file;
 			struct socket *sock;
-			unsigned long s;
-			int rv, err = 0;
+			int err;
 
 			file = fcheck_files(files, fd);
 			if (!file)
 				continue;
 
-			path = d_path(&file->f_path, tmp, PAGE_SIZE);
-			rv = sscanf(path, "socket:[%lu]", &s);
-			if (rv <= 0)
-				continue;
-
 			sock = sock_from_file(file, &err);
-			if (!err)
+			if (sock)
 				sock_update_netprioidx(sock->sk, p);
 		}
-		rcu_read_unlock();
+		spin_unlock(&files->file_lock);
 		task_unlock(p);
 	}
 	kfree(tmp);

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..053bd43 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)

@@ -282,6 +284,9 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 		/* Bump the usage count and install the file. */
 		get_file(fp[i]);
 		fd_install(new_fd, fp[i]);
+		sock = sock_from_file(fp[i], &err);
+		if (sock)
+			sock->sk->sk_cgrp_prioidx = prioidx;
 	}
 
 	if (i > 0)

On Mon, Aug 13, 2012 at 06:39:45PM -0700, John Fastabend wrote:

 		/* Bump the usage count and install the file. */
 		get_file(fp[i]);
 		fd_install(new_fd, fp[i]);
+		sock = sock_from_file(fp[i], &err);
+		if (sock)
+			sock->sk->sk_cgrp_prioidx = prioidx;

Better to do that before fd_install() exposes the sucker; it's not
a serious issue, but it's more obviously correct that way.

On 8/13/2012 7:31 PM, Al Viro wrote:

On Mon, Aug 13, 2012 at 06:39:45PM -0700, John Fastabend wrote:

quoted

  		/* Bump the usage count and install the file. */
  		get_file(fp[i]);
  		fd_install(new_fd, fp[i]);
+		sock = sock_from_file(fp[i], &err);
+		if (sock)
+			sock->sk->sk_cgrp_prioidx = prioidx;

Better to do that before fd_install() exposes the sucker; it's not
a serious issue, but it's more obviously correct that way.

Right. Moved it in v2.

On Mon, Aug 13, 2012 at 06:39:39PM -0700, John Fastabend wrote:

-			path = d_path(&file->f_path, tmp, PAGE_SIZE);

What's using tmp after that patch and do you still need to bother
allocating it?

On 8/13/2012 7:29 PM, Al Viro wrote:

On Mon, Aug 13, 2012 at 06:39:39PM -0700, John Fastabend wrote:

quoted

-			path = d_path(&file->f_path, tmp, PAGE_SIZE);

What's using tmp after that patch and do you still need to bother
allocating it?

nothing removed it in v2.