Patch "ppp: ensure file->private_data can't be overridden" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    ppp: ensure file->private_data can't be overridden

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ppp-ensure-file-private_data-can-t-be-overridden.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Sat Apr 16 10:02:53 PDT 2016
From: Guillaume Nault <g.nault@alphalink.fr>
Date: Mon, 14 Mar 2016 21:17:16 +0100
Subject: ppp: ensure file->private_data can't be overridden

From: Guillaume Nault <g.nault@alphalink.fr>

[ Upstream commit e8e56ffd9d2973398b60ece1f1bebb8d67b4d032 ]

Locking ppp_mutex must be done before dereferencing file->private_data,
otherwise it could be modified before ppp_unattached_ioctl() takes the
lock. This could lead ppp_unattached_ioctl() to override ->private_data,
thus leaking reference to the ppp_file previously pointed to.

v2: lock all ppp_ioctl() instead of just checking private_data in
    ppp_unattached_ioctl(), to avoid ambiguous behaviour.

Fixes: f3ff8a4d80e8 ("ppp: push BKL down into the driver")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ppp/ppp_generic.c |   31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -567,7 +567,7 @@ static int get_filter(void __user *arg,
 
 static long ppp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
-	struct ppp_file *pf = file->private_data;
+	struct ppp_file *pf;
 	struct ppp *ppp;
 	int err = -EFAULT, val, val2, i;
 	struct ppp_idle idle;
@@ -577,9 +577,14 @@ static long ppp_ioctl(struct file *file,
 	void __user *argp = (void __user *)arg;
 	int __user *p = argp;
 
-	if (!pf)
-		return ppp_unattached_ioctl(current->nsproxy->net_ns,
-					pf, file, cmd, arg);
+	mutex_lock(&ppp_mutex);
+
+	pf = file->private_data;
+	if (!pf) {
+		err = ppp_unattached_ioctl(current->nsproxy->net_ns,
+					   pf, file, cmd, arg);
+		goto out;
+	}
 
 	if (cmd == PPPIOCDETACH) {
 		/*
@@ -594,7 +599,6 @@ static long ppp_ioctl(struct file *file,
 		 * this fd and reopening /dev/ppp.
 		 */
 		err = -EINVAL;
-		mutex_lock(&ppp_mutex);
 		if (pf->kind == INTERFACE) {
 			ppp = PF_TO_PPP(pf);
 			rtnl_lock();
@@ -608,15 +612,13 @@ static long ppp_ioctl(struct file *file,
 		} else
 			pr_warn("PPPIOCDETACH file->f_count=%ld\n",
 				atomic_long_read(&file->f_count));
-		mutex_unlock(&ppp_mutex);
-		return err;
+		goto out;
 	}
 
 	if (pf->kind == CHANNEL) {
 		struct channel *pch;
 		struct ppp_channel *chan;
 
-		mutex_lock(&ppp_mutex);
 		pch = PF_TO_CHANNEL(pf);
 
 		switch (cmd) {
@@ -638,17 +640,16 @@ static long ppp_ioctl(struct file *file,
 				err = chan->ops->ioctl(chan, cmd, arg);
 			up_read(&pch->chan_sem);
 		}
-		mutex_unlock(&ppp_mutex);
-		return err;
+		goto out;
 	}
 
 	if (pf->kind != INTERFACE) {
 		/* can't happen */
 		pr_err("PPP: not interface or channel??\n");
-		return -EINVAL;
+		err = -EINVAL;
+		goto out;
 	}
 
-	mutex_lock(&ppp_mutex);
 	ppp = PF_TO_PPP(pf);
 	switch (cmd) {
 	case PPPIOCSMRU:
@@ -823,7 +824,10 @@ static long ppp_ioctl(struct file *file,
 	default:
 		err = -ENOTTY;
 	}
+
+out:
 	mutex_unlock(&ppp_mutex);
+
 	return err;
 }
 
@@ -836,7 +840,6 @@ static int ppp_unattached_ioctl(struct n
 	struct ppp_net *pn;
 	int __user *p = (int __user *)arg;
 
-	mutex_lock(&ppp_mutex);
 	switch (cmd) {
 	case PPPIOCNEWUNIT:
 		/* Create a new ppp unit */
@@ -886,7 +889,7 @@ static int ppp_unattached_ioctl(struct n
 	default:
 		err = -ENOTTY;
 	}
-	mutex_unlock(&ppp_mutex);
+
 	return err;
 }
 


Patches currently in stable-queue which might be from g.nault@alphalink.fr are

queue-4.4/ppp-release-rtnl-mutex-when-interface-creation-fails.patch
queue-4.4/ppp-take-reference-on-channels-netns.patch
queue-4.4/ppp-ensure-file-private_data-can-t-be-overridden.patch