staging: p9auth: prevent some oopses and memory leaks

Before all testcases, do:
mknod /dev/caphash c 253 0
mknod /dev/capuse c 253 1

This patch does the following:

1. caphash write of > CAP_NODE_SIZE bytes overruns node_ptr->data
(test: cat /etc/mime.types > /dev/caphash)
2. make sure we don't dereference a NULL cap_devices[0].head
(test: cat serge@root@abab > /dev/capuse)
3. don't let strlen dereference a NULL target_user etc
(test: echo ab > /dev/capuse)
4. Don't leak a bunch of memory in cap_write(). Note that
technically node_ptr is not needed for the capuse write case.
As a result I have a much more extensive patch splitting up
cap_write(), but I thought a smaller patch that is easier to test
and verify would be a better start. To test:
cnt=0
while [ 1 ]; do
echo /etc/mime.types > /dev/capuse
if [ $((cnt%25)) -eq 0 ]; then
head -2 /proc/meminfo
fi
cnt=$((cnt+1))
sleep 0.3
done
Without this patch, it MemFree steadily drops. With the patch,
it does not.

I have *not* tested this driver (with or without these patches)
with factotum or anything - only using the tests described above.

Signed-off-by: Serge E. Hallyn <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/p9auth/p9auth.c

···
 	if (down_interruptible(&dev->sem))
 		return -ERESTARTSYS;
 
+	user_buf_running = NULL;
+	hash_str = NULL;
 	node_ptr = kmalloc(sizeof(struct cap_node), GFP_KERNEL);
 	user_buf = kzalloc(count, GFP_KERNEL);
+	if (!node_ptr || !user_buf)
+		goto out;
 
 	if (copy_from_user(user_buf, buf, count)) {
 		retval = -EFAULT;
···
 	 * hashed capability supplied by the user to the list of hashes
 	 */
 	if (0 == iminor(filp->f_dentry->d_inode)) {
+		if (count > CAP_NODE_SIZE) {
+			retval = -EINVAL;
+			goto out;
+		}
 		printk(KERN_INFO "Capability being written to /dev/caphash : \n");
 		hexdump(user_buf, count);
 		memcpy(node_ptr->data, user_buf, count);
 		list_add(&(node_ptr->list), &(dev->head->list));
+		node_ptr = NULL;
 	} else {
+		if (!cap_devices[0].head ||
+				list_empty(&(cap_devices[0].head->list))) {
+			retval = -EINVAL;
+			goto out;
+		}
 		/*
 		 * break the supplied string into tokens with @ as the
 		 * delimiter If the string is "user1@user2@randomstring" we
···
 		source_user = strsep(&user_buf_running, "@");
 		target_user = strsep(&user_buf_running, "@");
 		rand_str = strsep(&user_buf_running, "@");
+		if (!source_user || !target_user || !rand_str) {
+			retval = -EINVAL;
+			goto out;
+		}
 
 		/* hash the string user1@user2 with rand_str as the key */
 		len = strlen(source_user) + strlen(target_user) + 1;
···
 			retval = -EFAULT;
 			goto out;
 		}
-		memcpy(node_ptr->data, result, CAP_NODE_SIZE);
+		memcpy(node_ptr->data, result, CAP_NODE_SIZE);  /* why? */
 		/* Change the process's uid if the hash is present in the
 		 * list of hashes
 		 */
···
 		dev->size = *f_pos;
 
 out:
+	kfree(node_ptr);
+	kfree(user_buf);
+	kfree(user_buf_running);
+	kfree(hash_str);
 	up(&dev->sem);
 	return retval;
 }