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| Started by | Jann Horn <jann@thejh.net> |
|---|---|
| First post | 2016-10-30 23:30 +0100 |
| Last post | 2016-11-10 15:00 +0100 |
| Articles | 5 — 4 participants |
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[PATCH v2] ppdev: fix double-free of pp->pdev->name Jann Horn <jann@thejh.net> - 2016-10-30 23:30 +0100
Re: [PATCH v2] ppdev: fix double-free of pp->pdev->name Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-11-10 12:40 +0100
Re: [PATCH v2] ppdev: fix double-free of pp->pdev->name Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2016-11-10 13:50 +0100
Re: [PATCH v2] ppdev: fix double-free of pp->pdev->name Arnd Bergmann <arnd@arndb.de> - 2016-11-10 14:20 +0100
Re: [PATCH v2] ppdev: fix double-free of pp->pdev->name Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2016-11-10 15:00 +0100
| From | Jann Horn <jann@thejh.net> |
|---|---|
| Date | 2016-10-30 23:30 +0100 |
| Subject | [PATCH v2] ppdev: fix double-free of pp->pdev->name |
| Message-ID | <sy6M1-2cQ-3@gated-at.bofh.it> |
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] ==========================================================
Signed-off-by: Jann Horn <jann@thejh.net>
---
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);
}
--
2.1.4
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| From | Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
|---|---|
| Date | 2016-11-10 12:40 +0100 |
| Message-ID | <sBVS1-5xN-1@gated-at.bofh.it> |
| In reply to | #1512222 |
On Sun, Oct 30, 2016 at 11:19:24PM +0100, 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] ========================================================== > > Signed-off-by: Jann Horn <jann@thejh.net> > --- > drivers/char/ppdev.c | 3 --- > 1 file changed, 3 deletions(-) Sudip, I need an ack here before I can take this...
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| From | Sudip Mukherjee <sudipm.mukherjee@gmail.com> |
|---|---|
| Date | 2016-11-10 13:50 +0100 |
| Message-ID | <sBWXL-6hP-3@gated-at.bofh.it> |
| In reply to | #1512222 |
On Sun, Oct 30, 2016 at 11:19:24PM +0100, 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] ========================================================== > > Signed-off-by: Jann Horn <jann@thejh.net> Acked-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
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| From | Arnd Bergmann <arnd@arndb.de> |
|---|---|
| Date | 2016-11-10 14:20 +0100 |
| Message-ID | <sBXqN-6H1-11@gated-at.bofh.it> |
| In reply to | #1512222 |
On Sunday, October 30, 2016 11:19:24 PM CET Jann Horn wrote:
> 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);
> }
>
I took a closer look at this and found that we also leak the name
that is passed in register_device() in the same file:
name = kasprintf(GFP_KERNEL, CHRDEV "%x", minor);
...
pdev = parport_register_dev_model(port, name, &ppdev_cb, minor);
parport_register_dev_model() copies the name using kstrdup() and
we should really free it after parport_register_dev_model().
It's not a huge problem, just leaking a few bytes of memory, but
the extra kfree() probably came from this confusion.
Arnd
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| From | Sudip Mukherjee <sudipm.mukherjee@gmail.com> |
|---|---|
| Date | 2016-11-10 15:00 +0100 |
| Message-ID | <sBY3v-6TP-19@gated-at.bofh.it> |
| In reply to | #1518969 |
On Thu, Nov 10, 2016 at 02:18:12PM +0100, Arnd Bergmann wrote:
> On Sunday, October 30, 2016 11:19:24 PM CET Jann Horn wrote:
> > 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);
> > }
> >
>
> I took a closer look at this and found that we also leak the name
> that is passed in register_device() in the same file:
>
> name = kasprintf(GFP_KERNEL, CHRDEV "%x", minor);
> ...
> pdev = parport_register_dev_model(port, name, &ppdev_cb, minor);
>
> parport_register_dev_model() copies the name using kstrdup() and
> we should really free it after parport_register_dev_model().
yes. I missed that while converting the driver to use device model.
Thanks. I will send a patch to fix this tonight.
>
> It's not a huge problem, just leaking a few bytes of memory, but
> the extra kfree() probably came from this confusion.
No, it was the old code which was not in the device-model. The old code
uses parport_register_device() which just uses the same string that is
passed to it and so it was freed while releasing the device.
Regards
Sudip
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