From: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
To: Jann Horn <jann@thejh.net>, Arnd Bergmann <arnd@arndb.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org, linux-parport@lists.infradead.org,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH] ppdev: fix double-free of pp->pdev->name
Date: Sun, 30 Oct 2016 23:24:27 +0530 [thread overview]
Message-ID: <581633D3.3080502@gmail.com> (raw)
In-Reply-To: <1477842248-2234-1-git-send-email-jann@thejh.net>
On Sunday 30 October 2016 09:14 PM, Jann Horn wrote:
> free_pardevice() is called by parport_unregister_device() and already frees
> pp->pdev->name, don't try to do it again.
>
> This bug causes kernel crashes.
>
> I found and verified this with KASAN and some added pr_emerg()s:
>
> [ 60.316568] pp_release: pp->pdev->name == ffff88039cb264c0
> [ 60.316692] free_pardevice: freeing par_dev->name at ffff88039cb264c0
> [ 60.316706] pp_release: kfree(ffff88039cb264c0)
> [ 60.316714] ==========================================================
> [ 60.316722] BUG: Double free or freeing an invalid pointer
> [ 60.316731] Unexpected shadow byte: 0xFB
> [ 60.316801] Object at ffff88039cb264c0, in cache kmalloc-32 size: 32
> [ 60.316813] Allocated:
> [ 60.316824] PID = 1695
> [ 60.316869] Freed:
> [ 60.316880] PID = 1695
> [ 60.316935] ==========================================================
>
> CCing Andy Lutomirski because I think this is what broke vmapped stacks
> for me - after applying this patch, vmapped stacks worked for me.
> Previously, I got oopses (and lockups) caused by area->pages[0] being
> 0x400000000 in __vunmap(), with area->pages being allocated in the kmalloc
> area.
I think the above should not be a part of the commit message.
It looks like a valid bug. As we have now started using the device model
from this release, so device_unregister() will finally call
free_pardevice() and that will free the name.
>
> Signed-off-by: Jann Horn <jann@thejh.net>
> ---
Acked-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
> drivers/char/ppdev.c | 3 ---
> 1 file changed, 3 deletions(-)
>
> diff --git a/drivers/char/ppdev.c b/drivers/char/ppdev.c
> index d23368874710..6af1ce04b3da 100644
> --- a/drivers/char/ppdev.c
> +++ b/drivers/char/ppdev.c
> @@ -748,10 +748,7 @@ static int pp_release(struct inode *inode, struct file *file)
> }
>
> if (pp->pdev) {
> - const char *name = pp->pdev->name;
> -
> parport_unregister_device(pp->pdev);
> - kfree(name);
> pp->pdev = NULL;
> pr_debug(CHRDEV "%x: unregistered pardevice\n", minor);
> }
>
next prev parent reply other threads:[~2016-10-30 17:54 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-30 15:44 [PATCH] ppdev: fix double-free of pp->pdev->name Jann Horn
2016-10-30 16:29 ` Andy Lutomirski
2016-10-30 16:47 ` Jann Horn
2016-10-30 17:54 ` Sudip Mukherjee [this message]
2016-10-30 18:00 ` Jann Horn
2016-10-30 22:12 ` Greg Kroah-Hartman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=581633D3.3080502@gmail.com \
--to=sudipm.mukherjee@gmail.com \
--cc=arnd@arndb.de \
--cc=gregkh@linuxfoundation.org \
--cc=jann@thejh.net \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-parport@lists.infradead.org \
--cc=luto@amacapital.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox