[ 19/58] staging: comedi: fix memory leak for saved channel list

[Greg Kroah-Hartman]

3.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ian Abbott <abbotti@xxxxxxxxx>

commit c8cad4c89ee3b15935c532210ae6ebb5c0a2734d upstream.

When `do_cmd_ioctl()` allocates memory for the kernel copy of a channel
list, it frees any previously allocated channel list in
`async->cmd.chanlist` and replaces it with the new one.  However, if the
device is ever removed (or "detached") the cleanup code in
`cleanup_device()` in "drivers.c" does not free this memory so it is
lost.

A sensible place to free the kernel copy of the channel list is in
`do_become_nonbusy()` as at that point the comedi asynchronous command
associated with the channel list is no longer valid.  Free the channel
list in `do_become_nonbusy()` instead of `do_cmd_ioctl()` and clear the
pointer to prevent it being freed more than once.

Note that `cleanup_device()` could be called at an inappropriate time
while the comedi device is open, but that's a separate bug not related
to this this patch.

Signed-off-by: Ian Abbott <abbotti@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/staging/comedi/comedi_fops.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1377,7 +1377,6 @@ static int do_cmd_ioctl(struct comedi_de
 		goto cleanup;
 	}
 
-	kfree(async->cmd.chanlist);
 	async->cmd = user_cmd;
 	async->cmd.data = NULL;
 	/* load channel/gain list */
@@ -2122,6 +2121,8 @@ void do_become_nonbusy(struct comedi_dev
 	if (async) {
 		comedi_reset_async_buf(async);
 		async->inttrig = NULL;
+		kfree(async->cmd.chanlist);
+		async->cmd.chanlist = NULL;
 	} else {
 		printk(KERN_ERR
 		       "BUG: (?) do_become_nonbusy called with async=0\n");


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