From: Jiri Slaby <jslaby@suse.cz>
To: b.zolnierkie@samsung.com
Cc: "Security Officers" <security@kernel.org>,
"Kyungtae Kim" <kt0755@gmail.com>,
"Anthony Liguori" <aliguori@amazon.com>,
"Jiri Slaby" <jslaby@suse.cz>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
"Srivatsa S. Bhat" <srivatsa@csail.mit.edu>,
linux-distros@vs.openwall.org, linux-fbdev@vger.kernel.org,
"Greg KH" <greg@kroah.com>, "Solar Designer" <solar@openwall.com>,
"Yang Yingliang" <yangyingliang@huawei.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
张云海 <zhangyunhai@nsfocus.com>
Subject: [PATCH] vgacon: fix out of bounds write to the scrollback buffer
Date: Wed, 29 Jul 2020 09:02:49 +0200 [thread overview]
Message-ID: <20200729070249.20892-1-jslaby@suse.cz> (raw)
The current vgacon's scroll up implementation uses a circural buffer
in vgacon_scrollback_cur. It always advances tail to prepare it for the
next write and caps it to zero if the next ->vc_size_row bytes won't fit.
But when we change the VT size (e.g. by VT_RESIZE) in the meantime, the new
line might not fit to the end of the scrollback buffer in the next
attempt to scroll. This leads to various crashes as
vgacon_scrollback_update writes out of the buffer:
BUG: unable to handle page fault for address: ffffc900001752a0
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
RIP: 0010:mutex_unlock+0x13/0x30
...
Call Trace:
n_tty_write+0x1a0/0x4d0
tty_write+0x1a0/0x2e0
Or to KASAN reports:
BUG: KASAN: slab-out-of-bounds in vgacon_scroll+0x57a/0x8ed
So check whether the line fits in the buffer and wrap if needed. Do it
before the loop as console_sem is held and ->vc_size_row cannot change
during the execution of vgacon_scrollback_cur. If it does change, we
need to ensure it does not change elsewhere, not here.
Also, we do not split the write of a line into chunks as that would
break the consumers of the buffer. They expect ->cnt, ->tail and ->size
to be in harmony and advanced by ->vc_size_row.
I found few reports of this in the past, some with patches included,
some even 2 years old:
https://lore.kernel.org/lkml/CAEAjamsJnG-=TSOwgRbbb3B9Z-PA63oWmNPoKYWQ=Z=+X49akg@mail.gmail.com/
https://lore.kernel.org/lkml/1589336932-35508-1-git-send-email-yangyingliang@huawei.com/
This fixes CVE-2020-14331.
Big thanks to guys mentioned in the Reported-and-debugged-by lines below
who actually found the root cause.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-and-debugged-by: 张云海 <zhangyunhai@nsfocus.com>
Reported-and-debugged-by: Yang Yingliang <yangyingliang@huawei.com>
Reported-by: Kyungtae Kim <kt0755@gmail.com>
Fixes: 15bdab959c9b ([PATCH] vgacon: Add support for soft scrollback)
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Greg KH <greg@kroah.com>
Cc: Solar Designer <solar@openwall.com>
Cc: "Srivatsa S. Bhat" <srivatsa@csail.mit.edu>
Cc: Anthony Liguori <aliguori@amazon.com>
Cc: Security Officers <security@kernel.org>
Cc: linux-distros@vs.openwall.org
Cc: Yang Yingliang <yangyingliang@huawei.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
---
drivers/video/console/vgacon.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index f0f3d573f848..13194bb246f8 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c
@@ -250,6 +250,11 @@ static void vgacon_scrollback_update(struct vc_data *c, int t, int count)
p = (void *) (c->vc_origin + t * c->vc_size_row);
+ /* vc_size_row might have changed by VT_RESIZE in the meantime */
+ if ((vgacon_scrollback_cur->tail + c->vc_size_row) >=
+ vgacon_scrollback_cur->size)
+ vgacon_scrollback_cur->tail = 0;
+
while (count--) {
scr_memcpyw(vgacon_scrollback_cur->data +
vgacon_scrollback_cur->tail,
--
2.28.0
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
next reply other threads:[~2020-07-29 7:02 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20200729070257eucas1p1f5841756104301e67907136e45d6e9f5@eucas1p1.samsung.com>
2020-07-29 7:02 ` Jiri Slaby [this message]
2020-07-29 7:53 ` [PATCH] vgacon: fix out of bounds write to the scrollback buffer 张云海
2020-07-29 8:11 ` Jiri Slaby
2020-07-29 8:19 ` 张云海
2020-07-29 11:20 ` Jiri Slaby
2020-07-29 13:37 ` Bartlomiej Zolnierkiewicz
[not found] <20200729130710.GA13262@openwall.com>
[not found] ` <b764c575-70be-80dd-6718-e84370a7b2b3@nsfocus.com>
2020-07-30 6:46 ` Jiri Slaby
2020-07-30 7:38 ` Jiri Slaby
2020-07-30 10:39 ` 张云海
2020-07-31 5:22 ` 张云海
2020-08-03 8:08 ` Jiri Slaby
2020-08-03 8:18 ` Greg KH
2020-08-03 8:45 ` Daniel Vetter
2020-08-03 9:47 ` Greg KH
2020-08-03 11:07 ` Bartlomiej Zolnierkiewicz
2020-08-04 7:37 ` Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200729070249.20892-1-jslaby@suse.cz \
--to=jslaby@suse.cz \
--cc=aliguori@amazon.com \
--cc=b.zolnierkie@samsung.com \
--cc=dri-devel@lists.freedesktop.org \
--cc=greg@kroah.com \
--cc=kt0755@gmail.com \
--cc=linux-distros@vs.openwall.org \
--cc=linux-fbdev@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=security@kernel.org \
--cc=solar@openwall.com \
--cc=srivatsa@csail.mit.edu \
--cc=torvalds@linux-foundation.org \
--cc=yangyingliang@huawei.com \
--cc=zhangyunhai@nsfocus.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).