staging: comedi: fix memory leak for saved channel list

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associated with the channel list is no longer valid.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@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index c08c719..9465bce 100644 (file)
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1088,7 +1088,6 @@ static int do_cmd_ioctl(struct comedi_device *dev,
                goto cleanup;
        }
 
-       kfree(async->cmd.chanlist);
        async->cmd = user_cmd;
        async->cmd.data = NULL;
        /* load channel/gain list */
@@ -1833,6 +1832,8 @@ void do_become_nonbusy(struct comedi_device *dev, struct comedi_subdevice *s)
        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");