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staging: comedi: fix memory leak / bad pointer freeing for chanlist

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As a follow-up to commit 6cab7a37f5 ("staging: comedi: (regression)
channel list must be set for COMEDI_CMD ioctl"), Hartley Sweeten pointed
out another couple of bugs stemming from commit 6cab7a37f5 ("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: c6cd0eefb2 ("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: 6cab7a37f5
Cc: <stable@vger.kernel.org> # 3.15.y 3.16.y 3.17.y

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Ian Abbott 2014-10-20 15:10:40 +01:00 committed by Greg Kroah-Hartman
parent 0ea6fa037e
commit 238b5ad855
1 changed files with 3 additions and 0 deletions
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3
drivers/staging/comedi/comedi_fops.c
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@ -1462,6 +1462,7 @@ static int __comedi_get_user_chanlist(struct comedi_device *dev,
unsigned int *chanlist;
int ret;
cmd->chanlist = NULL;
chanlist = memdup_user(user_chanlist,
cmd->chanlist_len * sizeof(unsigned int));
if (IS_ERR(chanlist))
@ -1615,6 +1616,8 @@ static int do_cmdtest_ioctl(struct comedi_device *dev,
ret = s->do_cmdtest(dev, s, &cmd);
kfree(cmd.chanlist); /* free kernel copy of user chanlist */
/* restore chanlist pointer before copying back */
cmd.chanlist = (unsigned int __force *)user_chanlist;