From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Peilin Ye <yepeilin.cs@gmail.com>,
Jiri Slaby <jirislaby@kernel.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
linux-kernel-mentees@lists.linuxfoundation.org,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers
Date: Wed, 30 Sep 2020 13:52:11 +0200 [thread overview]
Message-ID: <20200930115211.GC1603625@kroah.com> (raw)
In-Reply-To: <CAKMK7uFzWZgs4rvqSXqn_ifr8utG_rNw54+y6CWjdV=Epak-iQ@mail.gmail.com>
On Wed, Sep 30, 2020 at 01:25:14PM +0200, Daniel Vetter wrote:
> On Wed, Sep 30, 2020 at 12:56 PM Peilin Ye <yepeilin.cs@gmail.com> wrote:
> >
> > On Wed, Sep 30, 2020 at 11:53:17AM +0200, Daniel Vetter wrote:
> > > On Wed, Sep 30, 2020 at 03:11:51AM -0400, Peilin Ye wrote:
> > > > On Tue, Sep 29, 2020 at 04:38:49PM +0200, Daniel Vetter wrote:
> > > > > On Tue, Sep 29, 2020 at 2:34 PM Peilin Ye <yepeilin.cs@gmail.com> wrote:
> > > > > > Ah, and speaking of built-in fonts, see fbcon_startup():
> > > > > >
> > > > > > /* Setup default font */
> > > > > > [...]
> > > > > > vc->vc_font.charcount = 256; /* FIXME Need to support more fonts */
> > > > > > ^^^^^^^^^^^^^^^
> > > > > >
> > > > > > This is because find_font() and get_default_font() return a `struct
> > > > > > font_desc *`, but `struct font_desc` doesn't contain `charcount`. I
> > > > > > think we also need to add a `charcount` field to `struct font_desc`.
> > > > >
> > > > > Hm yeah ... I guess maybe struct font_desc should be the starting
> > > > > point for the kernel internal font structure. It's at least there
> > > > > already ...
> > > >
> > > > I see, that will also make handling built-in fonts much easier!
> > >
> > > I think the only downside with starting with font_desc as the internal
> > > font represenation is that there's a few fields we don't need/have for
> > > userspace fonts (like the id/name stuff). So any helpers to e.g. print out
> > > font information need to make sure they don't trip over that
> > >
> > > But otherwise I don't see a problem with this, I think.
> >
> > Yes, and built-in fonts don't use refcount. Or maybe we can let
> > find_font() and get_default_font() kmalloc() a copy of built-in font
> > data, then keep track of refcount for both user and built-in fonts, but
> > that will waste a few K of memory for each built-in font we use...
>
> A possible trick for this would be to make sure built-in fonts start
> out with a refcount of 1. So never get freed. Plus maybe a check that
> if the name is set, then it's a built-in font and if we ever underflow
> the refcount we just WARN, but don't free anything.
>
> Another trick would be kern_font_get/put wrappers (we'd want those
> anyway if the userspace fonts are refcounted) and if kern_font->name
> != NULL (i.e. built-in font with name) then we simply don't call
> kref_get/put.
Ick, don't do that, the first trick of having them start out with an
increased reference count is the best way here. Makes the code simpler
and no special cases for the tear-down path.
thanks,
greg k-h
next prev parent reply other threads:[~2020-09-30 11:52 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-10 4:35 KASAN: global-out-of-bounds Read in fbcon_get_font syzbot
2020-01-01 17:40 ` syzbot
2020-09-24 13:38 ` [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers Peilin Ye
2020-09-24 13:40 ` [PATCH 1/3] fbdev, newport_con: Move FONT_EXTRA_WORDS macros into linux/font.h Peilin Ye
2020-09-24 13:42 ` [PATCH 2/3] Fonts: Support FONT_EXTRA_WORDS macros for built-in fonts Peilin Ye
2020-09-24 13:43 ` [PATCH 3/3] fbcon: Fix global-out-of-bounds read in fbcon_get_font() Peilin Ye
2020-09-24 14:09 ` [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers Greg Kroah-Hartman
2020-09-24 14:25 ` Peilin Ye
2020-09-24 14:42 ` David Laight
2020-09-24 15:30 ` Peilin Ye
2020-09-24 15:45 ` Dan Carpenter
2020-09-24 16:59 ` Peilin Ye
2020-09-25 8:38 ` Daniel Vetter
2020-09-25 6:46 ` Jiri Slaby
2020-09-25 10:13 ` Peilin Ye
2020-09-25 13:25 ` Daniel Vetter
2020-09-25 15:35 ` Peilin Ye
2020-09-29 9:09 ` Daniel Vetter
2020-09-29 9:44 ` Peilin Ye
2020-09-29 12:34 ` Peilin Ye
2020-09-29 14:38 ` Daniel Vetter
2020-09-30 7:11 ` Peilin Ye
2020-09-30 9:53 ` Daniel Vetter
2020-09-30 10:55 ` Peilin Ye
2020-09-30 11:25 ` Daniel Vetter
2020-09-30 11:52 ` Greg Kroah-Hartman [this message]
2020-09-30 12:58 ` Peilin Ye
2020-09-30 5:26 ` Jiri Slaby
2020-09-30 7:16 ` Peilin Ye
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