netdev - [PATCH] isdn/i4l: fetch the ppp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 19 Sep 2017 21:49:55 -0400
From:   Meng Xu <mengxu.gatech@...il.com>
To:     isdn@...ux-pingi.de, davem@...emloft.net, johannes.berg@...el.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     meng.xu@...ech.edu, sanidhya@...ech.edu, taesoo@...ech.edu,
        Meng Xu <mengxu.gatech@...il.com>
Subject: [PATCH] isdn/i4l: fetch the ppp_write buffer in one shot

In isdn_ppp_write(), the header (i.e., protobuf) of the buffer is
fetched twice from userspace. The first fetch is used to peek at the
protocol of the message and reset the huptimer if necessary; while the
second fetch copies in the whole buffer. However, given that buf resides
in userspace memory, a user process can race to change its memory content
across fetches. By doing so, we can either avoid resetting the huptimer
for any type of packets (by first setting proto to PPP_LCP and later
change to the actual type) or force resetting the huptimer for LCP
packets.

This patch changes this double-fetch behavior into two single fetches
decided by condition (lp->isdn_device < 0 || lp->isdn_channel <0).
A more detailed discussion can be found at
https://marc.info/?l=linux-kernel&m=150586376926123&w=2

Signed-off-by: Meng Xu <mengxu.gatech@...il.com>
---
 drivers/isdn/i4l/isdn_ppp.c | 37 +++++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/drivers/isdn/i4l/isdn_ppp.c b/drivers/isdn/i4l/isdn_ppp.c
index 6c44609..cd2b3c6 100644
--- a/drivers/isdn/i4l/isdn_ppp.c
+++ b/drivers/isdn/i4l/isdn_ppp.c
@@ -825,7 +825,6 @@ isdn_ppp_write(int min, struct file *file, const char __user *buf, int count)
 	isdn_net_local *lp;
 	struct ippp_struct *is;
 	int proto;
-	unsigned char protobuf[4];
 
 	is = file->private_data;
 
@@ -839,24 +838,28 @@ isdn_ppp_write(int min, struct file *file, const char __user *buf, int count)
 	if (!lp)
 		printk(KERN_DEBUG "isdn_ppp_write: lp == NULL\n");
 	else {
-		/*
-		 * Don't reset huptimer for
-		 * LCP packets. (Echo requests).
-		 */
-		if (copy_from_user(protobuf, buf, 4))
-			return -EFAULT;
-		proto = PPP_PROTOCOL(protobuf);
-		if (proto != PPP_LCP)
-			lp->huptimer = 0;
+		if (lp->isdn_device < 0 || lp->isdn_channel < 0) {
+			unsigned char protobuf[4];
+			/*
+			 * Don't reset huptimer for
+			 * LCP packets. (Echo requests).
+			 */
+			if (copy_from_user(protobuf, buf, 4))
+				return -EFAULT;
+
+			proto = PPP_PROTOCOL(protobuf);
+			if (proto != PPP_LCP)
+				lp->huptimer = 0;
 
-		if (lp->isdn_device < 0 || lp->isdn_channel < 0)
 			return 0;
+		}
 
 		if ((dev->drv[lp->isdn_device]->flags & DRV_FLAG_RUNNING) &&
 		    lp->dialstate == 0 &&
 		    (lp->flags & ISDN_NET_CONNECTED)) {
 			unsigned short hl;
 			struct sk_buff *skb;
+			unsigned char *cpy_buf;
 			/*
 			 * we need to reserve enough space in front of
 			 * sk_buff. old call to dev_alloc_skb only reserved
@@ -869,11 +872,21 @@ isdn_ppp_write(int min, struct file *file, const char __user *buf, int count)
 				return count;
 			}
 			skb_reserve(skb, hl);
-			if (copy_from_user(skb_put(skb, count), buf, count))
+			cpy_buf = skb_put(skb, count);
+			if (copy_from_user(cpy_buf, buf, count))
 			{
 				kfree_skb(skb);
 				return -EFAULT;
 			}
+
+			/*
+			 * Don't reset huptimer for
+			 * LCP packets. (Echo requests).
+			 */
+			proto = PPP_PROTOCOL(cpy_buf);
+			if (proto != PPP_LCP)
+				lp->huptimer = 0;
+
 			if (is->debug & 0x40) {
 				printk(KERN_DEBUG "ppp xmit: len %d\n", (int) skb->len);
 				isdn_ppp_frame_log("xmit", skb->data, skb->len, 32, is->unit, lp->ppp_slot);
-- 
2.7.4