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Baokun Li 3cbf0e392f ubi: Fix race condition between ctrl_cdev_ioctl and ubi_cdev_ioctl 
Hulk Robot reported a KASAN report about use-after-free:
 ==================================================================
 BUG: KASAN: use-after-free in __list_del_entry_valid+0x13d/0x160
 Read of size 8 at addr ffff888035e37d98 by task ubiattach/1385
 [...]
 Call Trace:
  klist_dec_and_del+0xa7/0x4a0
  klist_put+0xc7/0x1a0
  device_del+0x4d4/0xed0
  cdev_device_del+0x1a/0x80
  ubi_attach_mtd_dev+0x2951/0x34b0 [ubi]
  ctrl_cdev_ioctl+0x286/0x2f0 [ubi]

 Allocated by task 1414:
  device_add+0x60a/0x18b0
  cdev_device_add+0x103/0x170
  ubi_create_volume+0x1118/0x1a10 [ubi]
  ubi_cdev_ioctl+0xb7f/0x1ba0 [ubi]

 Freed by task 1385:
  cdev_device_del+0x1a/0x80
  ubi_remove_volume+0x438/0x6c0 [ubi]
  ubi_cdev_ioctl+0xbf4/0x1ba0 [ubi]
 [...]
 ==================================================================

The lock held by ctrl_cdev_ioctl is ubi_devices_mutex, but the lock held
by ubi_cdev_ioctl is ubi->device_mutex. Therefore, the two locks can be
concurrent.

ctrl_cdev_ioctl contains two operations: ubi_attach and ubi_detach.
ubi_detach is bug-free because it uses reference counting to prevent
concurrency. However, uif_init and uif_close in ubi_attach may race with
ubi_cdev_ioctl.

uif_init will race with ubi_cdev_ioctl as in the following stack.
           cpu1                   cpu2                  cpu3
_______________________|________________________|______________________
ctrl_cdev_ioctl
 ubi_attach_mtd_dev
  uif_init
                           ubi_cdev_ioctl
                            ubi_create_volume
                             cdev_device_add
   ubi_add_volume
   // sysfs exist
   kill_volumes
                                                    ubi_cdev_ioctl
                                                     ubi_remove_volume
                                                      cdev_device_del
                                                       // first free
    ubi_free_volume
     cdev_del
     // double free
   cdev_device_del

And uif_close will race with ubi_cdev_ioctl as in the following stack.
           cpu1                   cpu2                  cpu3
_______________________|________________________|______________________
ctrl_cdev_ioctl
 ubi_attach_mtd_dev
  uif_init
                           ubi_cdev_ioctl
                            ubi_create_volume
                             cdev_device_add
  ubi_debugfs_init_dev
  //error goto out_uif;
  uif_close
   kill_volumes
                                                    ubi_cdev_ioctl
                                                     ubi_remove_volume
                                                      cdev_device_del
                                                       // first free
    ubi_free_volume
    // double free

The cause of this problem is that commit 714fb87e8b make device
"available" before it becomes accessible via sysfs. Therefore, we
roll back the modification. We will fix the race condition between
ubi device creation and udev by removing ubi_get_device in
vol_attribute_show and dev_attribute_show.This avoids accessing
uninitialized ubi_devices[ubi_num].

ubi_get_device is used to prevent devices from being deleted during
sysfs execution. However, now kernfs ensures that devices will not
be deleted before all reference counting are released.
The key process is shown in the following stack.

device_del
  device_remove_attrs
    device_remove_groups
      sysfs_remove_groups
        sysfs_remove_group
          remove_files
            kernfs_remove_by_name
              kernfs_remove_by_name_ns
                __kernfs_remove
                  kernfs_drain

Fixes: 714fb87e8b ("ubi: Fix race condition between ubi device creation and udev")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
History 2022-01-09 21:13:28 +01:00
arch Two small fixes, one of which was being worked around in selftests. 2021-12-19 12:44:03 -08:00
block block-5.16-2021-12-19 2021-12-19 12:38:53 -08:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto Update to zstd-1.4.10 2021-11-13 15:32:30 -08:00
Documentation ubifs: Document sysfs nodes 2021-12-23 20:23:42 +01:00
drivers
fs jffs2: GC deadlock reading a page that is used in jffs2_write_begin() 2021-12-23 22:33:41 +01:00
include Networking fixes for 5.16-rc6, including fixes from mac80211, wifi, bpf. 2021-12-16 15:02:14 -08:00
init kbuild: Fix -Wimplicit-fallthrough=5 error for GCC 5.x and 6.x 2021-11-14 18:59:49 -08:00
ipc shm: extend forced shm destroy to support objects from several IPC nses 2021-11-20 10:35:54 -08:00
kernel - Make sure the CLOCK_REALTIME to CLOCK_MONOTONIC offset is never positive 2021-12-19 12:23:18 -08:00
lib Merge https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 2021-12-08 16:06:44 -08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm Merge branch 'for-5.16-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu 2021-12-11 16:14:17 -08:00
net Networking fixes for 5.16-rc6, including fixes from mac80211, wifi, bpf. 2021-12-16 15:02:14 -08:00
samples ftrace/samples: Add module to test multi direct modify interface 2021-12-09 13:02:44 -05:00
scripts recordmcount.pl: look for jgnop instruction as well as bcrl on s390 2021-12-12 18:52:26 +01:00
security selinux: fix sleeping function called from invalid context 2021-12-16 17:47:39 -05:00
sound sound fixes for 5.16-rc5 2021-12-10 11:43:00 -08:00
tools Two small fixes, one of which was being worked around in selftests. 2021-12-19 12:44:03 -08:00
usr initramfs: Check timestamp to prevent broken cpio archive 2021-10-24 13:48:40 +09:00
virt KVM: downgrade two BUG_ONs to WARN_ON_ONCE 2021-11-26 06:43:28 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +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: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update email address for Guo Ren 2021-12-10 17:10:55 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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 ubifs: Document sysfs nodes 2021-12-23 20:23:42 +01:00
Makefile Linux 5.16-rc6 2021-12-19 14:14:33 -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.