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Date: Wed, 22 May 2019 16:06:56 +0800 From: Gen Zhang <blackgod016574@...il.com> To: Jiri Slaby <jslaby@...e.cz> Cc: linux-kernel@...r.kernel.org Subject: Re: [PATCH] tty_io: Fix a missing-check bug in drivers/tty/tty_io.c On Wed, May 22, 2019 at 06:25:36AM +0200, Jiri Slaby wrote: > On 22. 05. 19, 3:40, Gen Zhang wrote: > > In alloc_tty_struct(), tty->dev is assigned by tty_get_device(). And it > > calls class_find_device(). And class_find_device() may return NULL. > > And tty->dev is dereferenced in the following codes. When > > tty_get_device() returns NULL, dereferencing this tty->dev null pointer > > may cause the kernel go wrong. Thus we should check tty->dev. > > Further, if tty_get_device() returns NULL, we should free tty and > > return NULL. > > > > Signed-off-by: Gen Zhang <blackgod016574@...il.com> > > > > --- > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > > index 033ac7e..1444b59 100644 > > --- a/drivers/tty/tty_io.c > > +++ b/drivers/tty/tty_io.c > > @@ -3008,6 +3008,10 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx) > > tty->index = idx; > > tty_line_name(driver, idx, tty->name); > > tty->dev = tty_get_device(tty); > > + if (!tty->dev) { > > + kfree(tty); > > + return NULL; > > + } > > This is incorrect, you introduced an ldisc reference leak. Thanks for your reply, Jiri! And what do you mean by an ldisc reference leak? I did't get the reason of introducing it. > > And can this happen at all? I think tty_get_device() may happen to return NULL. Because it calls class_find_device() and there's a chance class_find_device() returns NULL. Thanks Gen > > thanks, > -- > js > suse labs
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