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Jiri Slaby 52c3c3a592 Revert "vc_screen: extract vcs_read_buf_header"
This reverts commit b1c32fcfad, because
Syzkaller reports a use-after-free, a write in vcs_read:

BUG: KASAN: use-after-free in vcs_read_buf drivers/tty/vt/vc_screen.c:357 [inline]
BUG: KASAN: use-after-free in vcs_read+0xaa7/0xb40 drivers/tty/vt/vc_screen.c:449
Write of size 2 at addr ffff8880a8014000 by task syz-executor.5/16936
CPU: 1 PID: 16936 Comm: syz-executor.5 Not tainted 5.9.0-rc1-next-20200820-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
...
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
 vcs_read_buf drivers/tty/vt/vc_screen.c:357 [inline]
 vcs_read+0xaa7/0xb40 drivers/tty/vt/vc_screen.c:449

There are two issues with the patch:
1) vcs_read rounds the 'count' *up* to an even number. So if we read odd
   bytes from the header (3 bytes in the reproducer), the second byte of
   a (2-byte/ushort) write to temporary con_buf won't fit. It is because
   with the patch applied, we only subtract the real number read (3 bytes)
   and not the whole header (4 bytes).

2) in this scenario, we perform unaligned accesses now: there are
   2-byte/ushort writes to odd addresses. Due to the same reason as
   above.

Revert this for now, re-think and retry later.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: syzbot+ad1f53726c3bd11180cb@syzkaller.appspotmail.com
Fixes: b1c32fcfad ("vc_screen: extract vcs_read_buf_header")
Cc: akpm@linux-foundation.org
Cc: nico@fluxnic.net
Link: https://lore.kernel.org/r/20200824095425.4376-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2020-08-24 19:51:56 +02:00
Documentation dt-bindings: timer: Add compatible for Mediatek MT8192 2020-08-19 07:46:42 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch parisc: fix PMD pages allocation by restoring pmd_alloc_one() 2020-08-16 10:53:13 -07:00
block block-5.9-2020-08-14 2020-08-15 20:36:42 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-08-14 13:09:15 -07:00
drivers Revert "vc_screen: extract vcs_read_buf_header" 2020-08-24 19:51:56 +02:00
fs io_uring-5.9-2020-08-15 2020-08-16 10:55:12 -07:00
include vc: propagate "viewed as bool" from screenpos up 2020-08-18 13:45:20 +02:00
init OpenRISC updates for 5.9 2020-08-14 14:04:53 -07:00
ipc ipc/shm.c: remove the superfluous break 2020-08-12 10:58:02 -07:00
kernel io_uring-5.9-2020-08-15 2020-08-16 10:55:12 -07:00
lib iomap: constify ioreadX() iomem argument (as in generic implementation) 2020-08-14 19:56:57 -07:00
mm Merge branch 'akpm' (patches from Andrew) 2020-08-15 08:02:03 -07:00
net 9p pull request for inclusion in 5.9 2020-08-15 08:34:36 -07:00
samples Kbuild updates for v5.9 2020-08-09 14:10:26 -07:00
scripts Kconfig updates for v5.9 2020-08-14 11:04:45 -07:00
security Merge branch 'akpm' (patches from Andrew) 2020-08-12 11:24:12 -07:00
sound sound fixes for 5.9-rc1 2020-08-14 15:58:57 -07:00
tools Cleanup, SECCOMP_FILTER support, message printing fixes, and other 2020-08-15 18:50:32 -07:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt Merge branch 'akpm' (patches from Andrew) 2020-08-12 11:24:12 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Add ZSTD-compressed files 2020-07-31 11:50:49 +02:00
.mailmap mailmap: add entry for Greg Kurz 2020-08-14 19:56:56 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Replace HTTP links with HTTPS ones 2020-07-23 14:53:58 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS perf tools changes for v5.9: 2nd batch 2020-08-15 11:17:15 -07:00
Makefile Linux 5.9-rc1 2020-08-16 13:04:57 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

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.