Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753710AbaJTVid (ORCPT ); Mon, 20 Oct 2014 17:38:33 -0400 Received: from p3plex2out02.prod.phx3.secureserver.net ([184.168.131.14]:42708 "EHLO p3plex2out02.prod.phx3.secureserver.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753671AbaJTVi2 convert rfc822-to-8bit (ORCPT ); Mon, 20 Oct 2014 17:38:28 -0400 From: Hartley Sweeten To: Ian Abbott , "driverdev-devel@linuxdriverproject.org" CC: Greg Kroah-Hartman , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Subject: RE: [PATCH] staging: comedi: fix memory leak / bad pointer freeing for chanlist Thread-Topic: [PATCH] staging: comedi: fix memory leak / bad pointer freeing for chanlist Thread-Index: AQHP7G+rXRnBcBAewE+DE6Migp8ASZw5gRbQ Date: Mon, 20 Oct 2014 21:38:27 +0000 Message-ID: References: <1413814240-3094-1-git-send-email-abbotti@mev.co.uk> In-Reply-To: <1413814240-3094-1-git-send-email-abbotti@mev.co.uk> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [184.183.19.121] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > Cc: # 3.15.y 3.16.y 3.17.y: 6cab7a37f5c04 > Cc: # 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. The remaining goto cleanup jumps will correctly free the kernel allocated pointer stored in cmd.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; > This one does fix the issue in do_cmdtest_ioctl(). Regards, Hartley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/