Messages in this thread |  | | Date | Sun, 30 Oct 2016 23:24:27 +0530 | From | Sudip Mukherjee <> | Subject | Re: [PATCH] ppdev: fix double-free of pp->pdev->name |
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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); > } >
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