From: Khalid Masum <khalid.masum.92@gmail.com>
To: Helge Deller <deller@gmx.de>,
syzbot <syzbot+14b0e8f3fd1612e35350@syzkaller.appspotmail.com>,
dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>
Subject: Re: [syzbot] KASAN: vmalloc-out-of-bounds Write in imageblit (2)
Date: Mon, 1 Aug 2022 10:09:45 +0600 [thread overview]
Message-ID: <3d33d2c6-ad56-a442-2458-5892138a4d9d@gmail.com> (raw)
In-Reply-To: <f15c9525-f21f-0599-3d5e-d9cbedc683df@gmx.de>
On 7/31/22 21:39, Helge Deller wrote:
> On 7/31/22 15:55, Khalid Masum wrote:
>> On 7/30/22 23:25, Helge Deller wrote:
>>> On 7/29/22 08:51, Khalid Masum wrote:
>>>> Here is a simplified reproducer for the issue:
>>>>
>>>> https://gist.githubusercontent.com/Labnann/923d6b9b3a19848fc129637b839b8a55/raw/a68271fcc724569735fe27f80817e561b3ff629a/reproducer.c
>>>
>>> The reproducer does this:
>>> ioctl(3, TIOCLINUX, TIOCL_SETSEL, selection: xs:3 ys:0 xe:0 ye:0 mode:0) = 0
>>> -> sets the text selection area
>>> ioctl(4, KDFONTOP) with op=0 (con_font_set), charcount=512 width=8 height=32, 0x20000000) = 0
>>> -> changes the font size.
>>>
>>> It does not crash with current Linus' head (v5.19-rc8).
>>> Kernel v5.16, which was used by this KASAN report, hasn't received backports
>>> since months, so I tried stable kernel v5.15.58 instead, and this
>>> kernel crashed with the reproducer.
>>>
>>> The reproducer brings up two issues with current code:
>>> 1. The reproducer uses ioctl(TIOCLINUX, TIOCL_SETSEL) and hands over (invalid)
>>> zero-values for ys and ye for the starting lines.
>>> This is wrong, since the API seems to expect a "1" as the very first line for the selection.
>>
>> Why do you think that API expects a 1?
>
> because the code in drivers/tty/vt/selection.c indicates this:
> See:
> static int vc_selection(struct vc_data *vc, struct tiocl_selection *v, struct tty_struct *tty)
> {
> int ps, pe;
> ...
> v->xs = min_t(u16, v->xs - 1, vc->vc_cols - 1);
> v->ys = min_t(u16, v->ys - 1, vc->vc_rows - 1);
> v->xe = min_t(u16, v->xe - 1, vc->vc_cols - 1);
> v->ye = min_t(u16, v->ye - 1, vc->vc_rows - 1);
> ...
> ps = v->ys * vc->vc_size_row + (v->xs << 1);
> pe = v->ye * vc->vc_size_row + (v->xe << 1);
>
> The userspace-provided xs,ys,xe and ye values are decremented by one
> before ps and pe (the pointers into the text screen array) are calculated.
> So, for the xs...ye values in the range from 1..max-screen-lines/columns
> are expected.
Oh. I got it. It is pretty simple. Thanks again for explaining.
>
> Helge
Khalid Masum
next prev parent reply other threads:[~2022-08-01 4:10 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-19 9:18 [syzbot] KASAN: vmalloc-out-of-bounds Write in imageblit (2) syzbot
2022-01-20 22:58 ` syzbot
2022-01-21 1:48 ` syzbot
2022-07-29 6:51 ` Khalid Masum
2022-07-30 17:25 ` Helge Deller
2022-07-30 18:49 ` [PATCH] tty: vt: selection: Add check for valid tiocl_selection values Helge Deller
2022-08-04 5:47 ` Jiri Slaby
2022-08-04 7:15 ` Helge Deller
2022-08-04 8:44 ` Helge Deller
2022-08-04 9:22 ` Jiri Slaby
2022-08-05 11:13 ` Adam Borowski
2022-08-05 11:13 ` Adam Borowski
2022-07-30 18:50 ` [PATCH] vt: Clear selection before changing the font Helge Deller
2022-07-31 11:32 ` Khalid Masum
2022-07-31 10:03 ` [syzbot] KASAN: vmalloc-out-of-bounds Write in imageblit (2) Khalid Masum
2022-07-31 10:54 ` Helge Deller
2022-07-31 10:54 ` Helge Deller
2022-07-31 11:23 ` Khalid Masum
2022-07-31 11:23 ` Khalid Masum
2022-07-31 13:55 ` Khalid Masum
2022-07-31 15:39 ` Helge Deller
2022-08-01 4:09 ` Khalid Masum [this message]
2022-07-30 8:12 ` Khalid Masum
2022-07-30 10:55 ` syzbot
2022-08-01 10:43 ` Dan Carpenter
2022-08-01 14:06 ` Khalid Masum
2022-07-30 11:45 ` Khalid Masum
2022-07-30 15:39 ` syzbot
2022-08-01 15:42 Khalid Masum
2022-08-01 15:53 ` syzbot
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