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Daiyue Zhang 14fbbc8297 configfs: fix a use-after-free in __configfs_open_file 
Commit b0841eefd9 ("configfs: provide exclusion between IO and removals")
uses ->frag_dead to mark the fragment state, thus no bothering with extra
refcount on config_item when opening a file. The configfs_get_config_item
was removed in __configfs_open_file, but not with config_item_put. So the
refcount on config_item will lost its balance, causing use-after-free
issues in some occasions like this:

Test:
1. Mount configfs on /config with read-only items:
drwxrwx--- 289 root   root            0 2021-04-01 11:55 /config
drwxr-xr-x   2 root   root            0 2021-04-01 11:54 /config/a
--w--w--w-   1 root   root         4096 2021-04-01 11:53 /config/a/1.txt
......

2. Then run:
for file in /config
do
echo $file
grep -R 'key' $file
done

3. __configfs_open_file will be called in parallel, the first one
got called will do:
if (file->f_mode & FMODE_READ) {
	if (!(inode->i_mode & S_IRUGO))
		goto out_put_module;
			config_item_put(buffer->item);
				kref_put()
					package_details_release()
						kfree()

the other one will run into use-after-free issues like this:
BUG: KASAN: use-after-free in __configfs_open_file+0x1bc/0x3b0
Read of size 8 at addr fffffff155f02480 by task grep/13096
CPU: 0 PID: 13096 Comm: grep VIP: 00 Tainted: G        W       4.14.116-kasan #1
TGID: 13096 Comm: grep
Call trace:
dump_stack+0x118/0x160
kasan_report+0x22c/0x294
__asan_load8+0x80/0x88
__configfs_open_file+0x1bc/0x3b0
configfs_open_file+0x28/0x34
do_dentry_open+0x2cc/0x5c0
vfs_open+0x80/0xe0
path_openat+0xd8c/0x2988
do_filp_open+0x1c4/0x2fc
do_sys_open+0x23c/0x404
SyS_openat+0x38/0x48

Allocated by task 2138:
kasan_kmalloc+0xe0/0x1ac
kmem_cache_alloc_trace+0x334/0x394
packages_make_item+0x4c/0x180
configfs_mkdir+0x358/0x740
vfs_mkdir2+0x1bc/0x2e8
SyS_mkdirat+0x154/0x23c
el0_svc_naked+0x34/0x38

Freed by task 13096:
kasan_slab_free+0xb8/0x194
kfree+0x13c/0x910
package_details_release+0x524/0x56c
kref_put+0xc4/0x104
config_item_put+0x24/0x34
__configfs_open_file+0x35c/0x3b0
configfs_open_file+0x28/0x34
do_dentry_open+0x2cc/0x5c0
vfs_open+0x80/0xe0
path_openat+0xd8c/0x2988
do_filp_open+0x1c4/0x2fc
do_sys_open+0x23c/0x404
SyS_openat+0x38/0x48
el0_svc_naked+0x34/0x38

To fix this issue, remove the config_item_put in
__configfs_open_file to balance the refcount of config_item.

Fixes: b0841eefd9 ("configfs: provide exclusion between IO and removals")
Signed-off-by: Daiyue Zhang <zhangdaiyue1@huawei.com>
Signed-off-by: Yi Chen <chenyi77@huawei.com>
Signed-off-by: Ge Qiu <qiuge@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
2021-03-11 12:13:48 +01:00
arch s390 updates for 5.12-rc3 2021-03-10 13:15:16 -08:00
block block/bfq: update comments and default value in docs for fifo_expire 2021-03-02 11:25:38 -07:00
certs certs: Replace K{U,G}IDT_INIT() with GLOBAL_ROOT_{U,G}ID 2021-01-21 16:16:10 +00:00
crypto crypto: mips/poly1305 - enable for all MIPS processors 2021-03-08 11:52:17 +01:00
Documentation Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
drivers s390 updates for 5.12-rc3 2021-03-10 13:15:16 -08:00
fs configfs: fix a use-after-free in __configfs_open_file 2021-03-11 12:13:48 +01:00
include Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
init kbuild: fix UNUSED_KSYMS_WHITELIST for Clang LTO 2021-02-28 15:19:21 +09:00
ipc fs: make helpers idmap mount aware 2021-01-24 14:27:20 +01:00
kernel Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
lib Merge git://git.kernel.org:/pub/scm/linux/kernel/git/davem/sparc 2021-03-08 22:01:58 -08:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm Revert "mm, slub: consider rest of partial list if acquire_slab() fails" 2021-03-10 10:18:04 -08:00
net Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
samples Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
scripts gcc-plugins fixes for v5.12-rc2 2021-03-05 17:23:03 -08:00
security Keyrings miscellany 2021-02-23 16:09:23 -08:00
sound ALSA: hda/realtek: Apply dual codec quirks for MSI Godlike X570 board 2021-03-03 15:25:03 +01:00
tools Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
usr Kbuild updates for v5.12 2021-02-25 10:17:31 -08:00
virt KVM: x86/mmu: Consider the hva in mmu_notifier retry 2021-02-22 13:16:53 -05:00
.clang-format cxl for 5.12 2021-02-24 09:38:36 -08:00
.cocciconfig
.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 clang-lto series for v5.12-rc1 2021-02-23 09:28:51 -08:00
.mailmap treewide: Miguel has moved 2021-02-26 09:41:03 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS treewide: Miguel has moved 2021-02-26 09:41:03 -08:00
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 Merge git://git.kernel.org:/pub/scm/linux/kernel/git/netdev/net 2021-03-09 17:15:56 -08:00
Makefile Linux 5.12-rc2 2021-03-05 17:33:41 -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.