From: Peilin Ye <yepeilin.cs@gmail.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Daniel Vetter <daniel@ffwll.ch>
Cc: Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
Jiri Slaby <jirislaby@kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
dri-devel <dri-devel@lists.freedesktop.org>,
linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers
Date: Wed, 30 Sep 2020 08:58:55 -0400 [thread overview]
Message-ID: <20200930125855.GA1155358@PWN> (raw)
In-Reply-To: <20200930115211.GC1603625@kroah.com>
On Wed, Sep 30, 2020 at 01:52:11PM +0200, Greg Kroah-Hartman wrote:
> 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:
> > > 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.
I see, I'll just let them start out with 1, and only check `->name !=
NULL` in kern_font_put(). Thank you!
Peilin Ye
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next prev parent reply other threads:[~2020-09-30 12:59 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <0000000000006b9e8d059952095e@google.com>
2020-09-24 13:38 ` [Linux-kernel-mentees] [PATCH 0/3] Prevent out-of-bounds access for built-in font data buffers Peilin Ye
2020-09-24 13:40 ` [Linux-kernel-mentees] [PATCH 1/3] fbdev, newport_con: Move FONT_EXTRA_WORDS macros into linux/font.h Peilin Ye
2020-09-24 13:42 ` [Linux-kernel-mentees] [PATCH 2/3] Fonts: Support FONT_EXTRA_WORDS macros for built-in fonts Peilin Ye
2020-09-24 13:43 ` [Linux-kernel-mentees] [PATCH 3/3] fbcon: Fix global-out-of-bounds read in fbcon_get_font() Peilin Ye
2020-09-24 14:09 ` [Linux-kernel-mentees] [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
2020-09-30 12:58 ` Peilin Ye [this message]
2020-09-30 5:26 ` Jiri Slaby
2020-09-30 7:16 ` Peilin Ye
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