From 31ebabbe9b33067b2bd2cb07ecc2e836c31e0435 Mon Sep 17 00:00:00 2001
From: Shaun Ruffell <sruffell@digium.com>
Date: Wed, 4 Aug 2010 12:29:33 -0500
Subject: [PATCH] dahdi: Better tolerate surprise removal of channels.

Enable DAHDI to detect if an operation on a open file handle refers to a
channel that may have been hot swapped out.

This is done by ensuring that file->private_data is always properly set for
any open channel, and it's set back to NULL when a channel is unregistered.
Then file->private_data can be used to check whether it's valid to perform an
operation on the channel.

(issue #17669)
Reported by: tzafrir
Tested by: sruffell
---
 drivers/dahdi/dahdi-base.c |   35 +++++++++++++++++++++++++----------
 1 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/drivers/dahdi/dahdi-base.c b/drivers/dahdi/dahdi-base.c
index a54bbeb..c345799 100644
--- a/drivers/dahdi/dahdi-base.c
+++ b/drivers/dahdi/dahdi-base.c
@@ -1966,6 +1966,12 @@ static void dahdi_chan_unreg(struct dahdi_chan *chan)
 
 	might_sleep();
 
+	/* In the case of surprise removal of hardware, make sure any open
+	 * file handles to this channel are disassociated with the actual
+	 * dahdi_chan. */
+	if (chan->file)
+		chan->file->private_data = NULL;
+
 	release_echocan(chan->ec_factory);
 
 #ifdef CONFIG_DAHDI_NET
@@ -2019,9 +2025,10 @@ static void dahdi_chan_unreg(struct dahdi_chan *chan)
 	write_unlock_irqrestore(&chan_lock, flags);
 }
 
-static ssize_t dahdi_chan_read(struct file *file, char __user *usrbuf, size_t count, int unit)
+static ssize_t dahdi_chan_read(struct file *file, char __user *usrbuf,
+			       size_t count)
 {
-	struct dahdi_chan *chan = chans[unit];
+	struct dahdi_chan *chan = file->private_data;
 	int amnt;
 	int res, rv;
 	int oldbuf,x;
@@ -2145,10 +2152,11 @@ static int num_filled_bufs(struct dahdi_chan *chan)
 	return range1 + range2;
 }
 
-static ssize_t dahdi_chan_write(struct file *file, const char __user *usrbuf, size_t count, int unit)
+static ssize_t dahdi_chan_write(struct file *file, const char __user *usrbuf,
+				size_t count)
 {
 	unsigned long flags;
-	struct dahdi_chan *chan = chans[unit];
+	struct dahdi_chan *chan = file->private_data;
 	int res, amnt, oldbuf, rv, x;
 
 	/* Make sure count never exceeds 65k, and make sure it's unsigned */
@@ -2743,6 +2751,7 @@ static int dahdi_specchan_open(struct file *file, int unit)
 			}
 			if (!res) {
 				chan->file = file;
+				file->private_data = chan;
 				spin_unlock_irqrestore(&chan->lock, flags);
 			} else {
 				spin_unlock_irqrestore(&chan->lock, flags);
@@ -2905,7 +2914,7 @@ static ssize_t dahdi_read(struct file *file, char __user *usrbuf, size_t count,
 		chan = file->private_data;
 		if (!chan)
 			return -EINVAL;
-		return dahdi_chan_read(file, usrbuf, count, chan->channo);
+		return dahdi_chan_read(file, usrbuf, count);
 	}
 
 	if (unit == 255) {
@@ -2914,12 +2923,12 @@ static ssize_t dahdi_read(struct file *file, char __user *usrbuf, size_t count,
 			module_printk(KERN_NOTICE, "No pseudo channel structure to read?\n");
 			return -EINVAL;
 		}
-		return dahdi_chan_read(file, usrbuf, count, chan->channo);
+		return dahdi_chan_read(file, usrbuf, count);
 	}
 	if (count < 0)
 		return -EINVAL;
 
-	return dahdi_chan_read(file, usrbuf, count, unit);
+	return dahdi_chan_read(file, usrbuf, count);
 }
 
 static ssize_t dahdi_write(struct file *file, const char __user *usrbuf, size_t count, loff_t *ppos)
@@ -2937,7 +2946,7 @@ static ssize_t dahdi_write(struct file *file, const char __user *usrbuf, size_t
 		chan = file->private_data;
 		if (!chan)
 			return -EINVAL;
-		return dahdi_chan_write(file, usrbuf, count, chan->channo);
+		return dahdi_chan_write(file, usrbuf, count);
 	}
 	if (unit == 255) {
 		chan = file->private_data;
@@ -2945,9 +2954,9 @@ static ssize_t dahdi_write(struct file *file, const char __user *usrbuf, size_t
 			module_printk(KERN_NOTICE, "No pseudo channel structure to read?\n");
 			return -EINVAL;
 		}
-		return dahdi_chan_write(file, usrbuf, count, chan->channo);
+		return dahdi_chan_write(file, usrbuf, count);
 	}
-	return dahdi_chan_write(file, usrbuf, count, unit);
+	return dahdi_chan_write(file, usrbuf, count);
 
 }
 
@@ -5863,6 +5872,12 @@ static int dahdi_ioctl(struct inode *inode, struct file *file,
 		ret = dahdi_chanandpseudo_ioctl(file, cmd, data, chan->channo);
 		goto unlock_exit;
 	}
+
+	if (!file->private_data) {
+		ret = -ENXIO;
+		goto unlock_exit;
+	}
+
 	ret = dahdi_chan_ioctl(file, cmd, data, unit);
 
 unlock_exit:
-- 
1.7.2