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Greg Kroah-Hartman fedb576064 serial: fix race between flush_to_ldisc and tty_open 
There still is a race window after the commit b027e2298b
("tty: fix data race between tty_init_dev and flush of buf"),
and we encountered this crash issue if receive_buf call comes
before tty initialization completes in tty_open and
tty->driver_data may be NULL.

CPU0                                    CPU1
----                                    ----
                                  tty_open
                                   tty_init_dev
                                     tty_ldisc_unlock
                                       schedule
flush_to_ldisc
 receive_buf
  tty_port_default_receive_buf
   tty_ldisc_receive_buf
    n_tty_receive_buf_common
      __receive_buf
       uart_flush_chars
        uart_start
        /*tty->driver_data is NULL*/
                                   tty->ops->open
                                   /*init tty->driver_data*/

it can be fixed by extending ldisc semaphore lock in tty_init_dev
to driver_data initialized completely after tty->ops->open(), but
this will lead to get lock on one function and unlock in some other
function, and hard to maintain, so fix this race only by checking
tty->driver_data when receiving, and return if tty->driver_data
is NULL, and n_tty_receive_buf_common maybe calls uart_unthrottle,
so add the same check.

Because the tty layer knows nothing about the driver associated with the
device, the tty layer can not do anything here, it is up to the tty
driver itself to check for this type of race.  Fix up the serial driver
to correctly check to see if it is finished binding with the device when
being called, and if not, abort the tty calls.

[Description and problem report and testing from Li RongQing, I rewrote
the patch to be in the serial layer, not in the tty core - gregkh]

Reported-by: Li RongQing <lirongqing@baidu.com>
Tested-by: Li RongQing <lirongqing@baidu.com>
Signed-off-by: Wang Li <wangli39@baidu.com>
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-01-31 19:43:04 +01:00
arch Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-01-27 12:02:00 -08:00
block Revert "block: cover another queue enter recursion via BIO_QUEUE_ENTERED" 2019-01-27 06:35:28 -07:00
certs kbuild: remove redundant target cleaning on failure 2019-01-06 09:46:51 +09:00
crypto crypto: sm3 - fix undefined shift by >= width of value 2019-01-10 21:37:32 +08:00
Documentation drm fixes. msm, sun4i, amdgpu, i915 gvt 2019-01-25 12:19:10 +13:00
drivers serial: fix race between flush_to_ldisc and tty_open 2019-01-31 19:43:04 +01:00
firmware kbuild: change filechk to surround the given command with { } 2019-01-06 09:46:51 +09:00
fs a set of small smb3 fixes, some fixing various crediting issues discovered during xfstest runs, five for stable 2019-01-26 15:38:22 -08:00
include Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-01-27 11:52:50 -08:00
init kbuild: Disable LD_DEAD_CODE_DATA_ELIMINATION with ftrace & GCC <= 4.7 2019-01-14 10:37:09 +09:00
ipc ipc: IPCMNI limit check for semmni 2018-10-31 08:54:14 -07:00
kernel Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-01-27 11:55:06 -08:00
lib XArray updates for 5.0-rc3 2019-01-22 17:08:30 +13:00
LICENSES This is a fairly typical cycle for documentation. There's some welcome 2018-10-24 18:01:11 +01:00
mm for-linus-20190125 2019-01-26 12:42:41 -08:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-01-27 08:59:12 -08:00
samples samples/bpf: workaround clang asm goto compilation errors 2019-01-15 20:57:30 +01:00
scripts Bug fixes for gcc-plugins 2019-01-21 13:07:03 +13:00
security Merge branch 'fixes-v5.0-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2019-01-17 16:54:58 +12:00
sound sound fixes for 5.0-rc4 2019-01-25 05:55:26 +13:00
tools Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-01-27 12:02:00 -08:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt KVM: validate userspace input in kvm_clear_dirty_log_protect() 2019-01-11 18:38:07 +01:00
.clang-format clang-format: Update .clang-format with the latest for_each macro list 2019-01-19 19:26:06 +01:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap A few early MIPS fixes for 4.21: 2019-01-05 12:48:25 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Add CREDITS entry for Shaohua Li 2019-01-04 14:27:09 -07:00
Kbuild kbuild: use assignment instead of define ... endef for filechk_* rules 2019-01-06 10:22:35 +09:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-01-27 08:59:12 -08:00
Makefile Linux 5.0-rc4 2019-01-27 15:18:05 -08:00
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.