Messages in this thread |  | | Date | Tue, 21 Oct 2014 09:43:47 +0100 | From | Ian Abbott <> | Subject | Re: [PATCH] staging: comedi: fix memory leak / bad pointer freeing for chanlist |
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On 20/10/14 22:38, Hartley Sweeten wrote: > On Monday, October 20, 2014 7:11 AM, Ian Abbott wrote: >> 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 >> --- >> Greg, this patch applies to your "staging-linus" branch. >> --- >> drivers/staging/comedi/comedi_fops.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c >> index a9b7fe5..a1788e8 100644 >> --- a/drivers/staging/comedi/comedi_fops.c >> +++ b/drivers/staging/comedi/comedi_fops.c >> @@ -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)) > > I don't think this covers all the problems in your second issue above. > > It does fix the attempt to free the memory pointed to by the user-space pointer > if the memdub_user() fails. > > But in do_cmd_ioctl() we still have an issue if the s->do_cmdtest() fails or > the CMDF_BOGUS flag is set. There we restore the users cmd.chanlist > pointer to allow copy_to_user() to return the cmd/ But the kernel allocated > chanlist is not freed. The goto cleanup will again try to free the user-space > pointer.
No, 'async->cmd' is copied (via struct assignment) to local variable 'cmd' and it is the local 'cmd.chanlist' pointer that is set to the original user-space pointer and the local 'cmd' that is copied back to user-space. 'async->cmd.chanlist' still points to the kernel copy of the chanlist that gets cleaned up by 'goto cleanup' / 'do_become_nonbusy().
-- -=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@mev.co.uk> )=- -=( Web: http://www.mev.co.uk/ )=-
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