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Baokun Li 3c6fc37be2 writeback, cgroup: fix null-ptr-deref write in bdi_split_work_to_wbs 
[ Upstream commit 1ba1199ec5 ]

KASAN report null-ptr-deref:
==================================================================
BUG: KASAN: null-ptr-deref in bdi_split_work_to_wbs+0x5c5/0x7b0
Write of size 8 at addr 0000000000000000 by task sync/943
CPU: 5 PID: 943 Comm: sync Tainted: 6.3.0-rc5-next-20230406-dirty #461
Call Trace:
 <TASK>
 dump_stack_lvl+0x7f/0xc0
 print_report+0x2ba/0x340
 kasan_report+0xc4/0x120
 kasan_check_range+0x1b7/0x2e0
 __kasan_check_write+0x24/0x40
 bdi_split_work_to_wbs+0x5c5/0x7b0
 sync_inodes_sb+0x195/0x630
 sync_inodes_one_sb+0x3a/0x50
 iterate_supers+0x106/0x1b0
 ksys_sync+0x98/0x160
[...]
==================================================================

The race that causes the above issue is as follows:

           cpu1                     cpu2
-------------------------|-------------------------
inode_switch_wbs
 INIT_WORK(&isw->work, inode_switch_wbs_work_fn)
 queue_rcu_work(isw_wq, &isw->work)
 // queue_work async
  inode_switch_wbs_work_fn
   wb_put_many(old_wb, nr_switched)
    percpu_ref_put_many
     ref->data->release(ref)
     cgwb_release
      queue_work(cgwb_release_wq, &wb->release_work)
      // queue_work async
       &wb->release_work
       cgwb_release_workfn
                            ksys_sync
                             iterate_supers
                              sync_inodes_one_sb
                               sync_inodes_sb
                                bdi_split_work_to_wbs
                                 kmalloc(sizeof(*work), GFP_ATOMIC)
                                 // alloc memory failed
        percpu_ref_exit
         ref->data = NULL
         kfree(data)
                                 wb_get(wb)
                                  percpu_ref_get(&wb->refcnt)
                                   percpu_ref_get_many(ref, 1)
                                    atomic_long_add(nr, &ref->data->count)
                                     atomic64_add(i, v)
                                     // trigger null-ptr-deref

bdi_split_work_to_wbs() traverses &bdi->wb_list to split work into all
wbs.  If the allocation of new work fails, the on-stack fallback will be
used and the reference count of the current wb is increased afterwards.
If cgroup writeback membership switches occur before getting the reference
count and the current wb is released as old_wd, then calling wb_get() or
wb_put() will trigger the null pointer dereference above.

This issue was introduced in v4.3-rc7 (see fix tag1).  Both
sync_inodes_sb() and __writeback_inodes_sb_nr() calls to
bdi_split_work_to_wbs() can trigger this issue.  For scenarios called via
sync_inodes_sb(), originally commit 7fc5854f8c ("writeback: synchronize
sync(2) against cgroup writeback membership switches") reduced the
possibility of the issue by adding wb_switch_rwsem, but in v5.14-rc1 (see
fix tag2) removed the "inode_io_list_del_locked(inode, old_wb)" from
inode_switch_wbs_work_fn() so that wb->state contains WB_has_dirty_io,
thus old_wb is not skipped when traversing wbs in bdi_split_work_to_wbs(),
and the issue becomes easily reproducible again.

To solve this problem, percpu_ref_exit() is called under RCU protection to
avoid race between cgwb_release_workfn() and bdi_split_work_to_wbs().
Moreover, replace wb_get() with wb_tryget() in bdi_split_work_to_wbs(),
and skip the current wb if wb_tryget() fails because the wb has already
been shutdown.

Link: https://lkml.kernel.org/r/20230410130826.1492525-1-libaokun1@huawei.com
Fixes: b817525a4a ("writeback: bdi_writeback iteration must not skip dying ones")
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Hou Tao <houtao1@huawei.com>
Cc: yangerkun <yangerkun@huawei.com>
Cc: Zhang Yi <yi.zhang@huawei.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2023-06-06 18:34:53 +08:00
arch KVM: nVMX: Emulate NOPs in L2, and PAUSE if it's not intercepted 2023-06-06 18:34:53 +08:00
block blk-crypto: make blk_crypto_evict_key() more robust 2023-06-06 18:34:51 +08:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2023-04-19 17:50:34 +08:00
crypto crypto: api - Demote BUG_ON() in crypto_unregister_alg() to a WARN_ON() 2023-06-06 18:34:52 +08:00
Documentation riscv: Move early dtb mapping into the fixmap region 2023-06-06 18:19:52 +08:00
drivers crypto: safexcel - Cleanup ring IRQ workqueues on load failure 2023-06-06 18:34:52 +08:00
fs writeback, cgroup: fix null-ptr-deref write in bdi_split_work_to_wbs 2023-06-06 18:34:53 +08:00
include tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem 2023-06-06 18:34:51 +08:00
init kbuild: Add CONFIG_PAHOLE_VERSION 2023-04-19 17:59:33 +08:00
io_uring io_uring: avoid null-ptr-deref in io_arm_poll_handler 2023-04-19 18:00:57 +08:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2023-04-19 17:56:54 +08:00
kernel relayfs: fix out-of-bounds access in relay_file_read 2023-06-06 18:34:53 +08:00
lib kobject: Fix slab-out-of-bounds in fill_kobj_path() 2023-04-19 18:00:00 +08:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm writeback, cgroup: fix null-ptr-deref write in bdi_split_work_to_wbs 2023-06-06 18:34:53 +08:00
net bluetooth: Perform careful capability checks in hci_sock_ioctl() 2023-06-06 18:07:05 +08:00
samples samples: vfio-mdev: Fix missing pci_disable_device() in mdpy_fb_probe() 2023-04-19 17:57:46 +08:00
scripts ASN.1: Fix check for strdup() success 2023-06-06 18:06:47 +08:00
security IMA: allow/fix UML builds 2023-06-06 18:34:50 +08:00
sound ASoC: Intel: bytcr_rt5640: Add quirk for the Acer Iconia One 7 B1-750 2023-06-06 18:34:49 +08:00
tools selftests mount: Fix mount_setattr_test builds failed 2023-06-06 18:34:49 +08:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2023-04-19 17:44:58 +08:00
virt KVM: fix memoryleak in kvm_init() 2023-04-19 18:00:47 +08:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.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: add Andrej Shadura 2021-10-18 20:22:03 -10:00
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 counter: Internalize sysfs interface code 2023-06-06 18:05:09 +08:00
Makefile Linux 5.15.110 2023-06-06 18:19:52 +08:00
README

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.