staging: comedi: fix memory leak / bad pointer freeing for chanlist
authorIan Abbott <abbotti@mev.co.uk>
Mon, 20 Oct 2014 14:10:40 +0000 (15:10 +0100)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Wed, 29 Oct 2014 08:18:31 +0000 (16:18 +0800)
commit238b5ad855924919e5b98d0c772d9dc78795639b
tree06c1c2a7cfa0947cfb36155a1b14d42e5a8f6fa3
parent0ea6fa037e961dc77cb2bb7a4ad91d172ee4884a
staging: comedi: fix memory leak / bad pointer freeing for chanlist

As a follow-up to commit 6cab7a37f5c04 ("staging: comedi: (regression)
channel list must be set for COMEDI_CMD ioctl"), Hartley Sweeten pointed
out another couple of bugs stemming from commit 6cab7a37f5c04 ("staging:
comedi: comedi_fops: introduce __comedi_get_user_chanlist()").

Firstly, `do_cmdtest_ioctl()` never frees the kernel copy of the user
chanlist allocated by `__comedi_get_user_chanlist()`, so that memory is
leaked.  Fix it by freeing the allocated kernel memory pointed to by
`cmd.chanlist` before that pointer is overwritten with its original
pointer to user memory before `cmd` is copied back to user-space.

Secondly, if `__comedi_get_user_chanlist()` returns an error,
`cmd->chanlist` is left unchanged and in fact will be a pointer to user
memory.  This causes `do_cmd_ioctl()` to `goto cleanup` and call
`do_become_nonbusy()` which would attempt to free the memory pointed to
by the user-space pointer.  Fix it by setting `cmd->chanlist` to NULL at
the start of `__comedi_get_user_chanlist()`.

Fixes: c6cd0eefb27b ("staging: comedi: comedi_fops: introduce __comedi_get_user_chanlist()")
Reported-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y: 6cab7a37f5c04
Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/staging/comedi/comedi_fops.c