ebfdfeeae8
vgacon_scrollback_update() always leaves enbough room in the scrollback
buffer for the next call, but if the console size changed that room
might not actually be enough, and so we need to re-check.
The check should be in the loop since vgacon_scrollback_cur->tail is
updated in the loop and count may be more than 1 when triggered by CSI M,
as Jiri's PoC:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
int main(int argc, char** argv)
{
int fd = open("/dev/tty1", O_RDWR);
unsigned short size[3] = {25, 200, 0};
ioctl(fd, 0x5609, size); // VT_RESIZE
write(fd, "\e[1;1H", 6);
for (int i = 0; i < 30; i++)
write(fd, "\e[10M", 5);
}
It 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
This fixes CVE-2020-14331.
Reported-by: 张云海 <zhangyunhai@nsfocus.com>
Reported-by: Yang Yingliang <yangyingliang@huawei.com>
Reported-by: Kyungtae Kim <kt0755@gmail.com>
Fixes: 15bdab959c9b ([PATCH] vgacon: Add support for soft scrollback)
Cc: stable@vger.kernel.org
Cc: linux-fbdev@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Solar Designer <solar@openwall.com>
Cc: "Srivatsa S. Bhat" <srivatsa@csail.mit.edu>
Cc: Anthony Liguori <aliguori@amazon.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Yunhai Zhang <zhangyunhai@nsfocus.com>
Link: https://lore.kernel.org/r/9fb43895-ca91-9b07-ebfd-808cf854ca95@nsfocus.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.