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linux/fs/proc
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Zhou Chengming 0b66ea3bca sysctl: Drop reference added by grab_header in proc_sys_readdir 
commit 93362fa47f upstream.

Fixes CVE-2016-9191, proc_sys_readdir doesn't drop reference
added by grab_header when return from !dir_emit_dots path.
It can cause any path called unregister_sysctl_table will
wait forever.

The calltrace of CVE-2016-9191:

[ 5535.960522] Call Trace:
[ 5535.963265]  [<ffffffff817cdaaf>] schedule+0x3f/0xa0
[ 5535.968817]  [<ffffffff817d33fb>] schedule_timeout+0x3db/0x6f0
[ 5535.975346]  [<ffffffff817cf055>] ? wait_for_completion+0x45/0x130
[ 5535.982256]  [<ffffffff817cf0d3>] wait_for_completion+0xc3/0x130
[ 5535.988972]  [<ffffffff810d1fd0>] ? wake_up_q+0x80/0x80
[ 5535.994804]  [<ffffffff8130de64>] drop_sysctl_table+0xc4/0xe0
[ 5536.001227]  [<ffffffff8130de17>] drop_sysctl_table+0x77/0xe0
[ 5536.007648]  [<ffffffff8130decd>] unregister_sysctl_table+0x4d/0xa0
[ 5536.014654]  [<ffffffff8130deff>] unregister_sysctl_table+0x7f/0xa0
[ 5536.021657]  [<ffffffff810f57f5>] unregister_sched_domain_sysctl+0x15/0x40
[ 5536.029344]  [<ffffffff810d7704>] partition_sched_domains+0x44/0x450
[ 5536.036447]  [<ffffffff817d0761>] ? __mutex_unlock_slowpath+0x111/0x1f0
[ 5536.043844]  [<ffffffff81167684>] rebuild_sched_domains_locked+0x64/0xb0
[ 5536.051336]  [<ffffffff8116789d>] update_flag+0x11d/0x210
[ 5536.057373]  [<ffffffff817cf61f>] ? mutex_lock_nested+0x2df/0x450
[ 5536.064186]  [<ffffffff81167acb>] ? cpuset_css_offline+0x1b/0x60
[ 5536.070899]  [<ffffffff810fce3d>] ? trace_hardirqs_on+0xd/0x10
[ 5536.077420]  [<ffffffff817cf61f>] ? mutex_lock_nested+0x2df/0x450
[ 5536.084234]  [<ffffffff8115a9f5>] ? css_killed_work_fn+0x25/0x220
[ 5536.091049]  [<ffffffff81167ae5>] cpuset_css_offline+0x35/0x60
[ 5536.097571]  [<ffffffff8115aa2c>] css_killed_work_fn+0x5c/0x220
[ 5536.104207]  [<ffffffff810bc83f>] process_one_work+0x1df/0x710
[ 5536.110736]  [<ffffffff810bc7c0>] ? process_one_work+0x160/0x710
[ 5536.117461]  [<ffffffff810bce9b>] worker_thread+0x12b/0x4a0
[ 5536.123697]  [<ffffffff810bcd70>] ? process_one_work+0x710/0x710
[ 5536.130426]  [<ffffffff810c3f7e>] kthread+0xfe/0x120
[ 5536.135991]  [<ffffffff817d4baf>] ret_from_fork+0x1f/0x40
[ 5536.142041]  [<ffffffff810c3e80>] ? kthread_create_on_node+0x230/0x230

One cgroup maintainer mentioned that "cgroup is trying to offline
a cpuset css, which takes place under cgroup_mutex.  The offlining
ends up trying to drain active usages of a sysctl table which apprently
is not happening."
The real reason is that proc_sys_readdir doesn't drop reference added
by grab_header when return from !dir_emit_dots path. So this cpuset
offline path will wait here forever.

See here for details: http://www.openwall.com/lists/oss-security/2016/11/04/13

Fixes: f0c3b5093a ("[readdir] convert procfs")
Reported-by: CAI Qian <caiqian@redhat.com>
Tested-by: Yang Shukui <yangshukui@huawei.com>
Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
History 2017-02-23 03:54:47 +00:00
..
array.c fs/proc, core/debug: Don't expose absolute kernel addresses via wchan 2015-12-13 17:49:51 +00:00
base.c fs: Give dentry to inode_change_ok() instead of inode 2017-02-23 03:53:52 +00:00
cmdline.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
consoles.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
cpuinfo.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
devices.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
fd.c proc: actually make proc_fd_permission() thread-friendly 2015-12-13 17:49:12 +00:00
fd.h proc: Move proc_fd() to fs/proc/fd.h 2013-05-01 17:29:39 -04:00
generic.c fs: Give dentry to inode_change_ok() instead of inode 2017-02-23 03:53:52 +00:00
inode.c proc: Allow creating permanently empty directories that serve as mount points 2015-07-15 10:01:06 +01:00
internal.h proc: Allow creating permanently empty directories that serve as mount points 2015-07-15 10:01:06 +01:00
interrupts.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
Kconfig kcore: add Kconfig help text 2013-11-13 12:09:33 +09:00
kcore.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
kmsg.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
loadavg.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
Makefile of: remove /proc/device-tree 2014-03-11 20:48:32 +00:00
meminfo.c fs/proc/meminfo: meminfo_proc_show(): fix typo in comment 2014-04-07 16:36:04 -07:00
namespaces.c new helper: readlink_copy() 2014-04-01 23:19:15 -04:00
nommu.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
page.c mm: close PageTail race 2014-03-04 07:55:47 -08:00
proc_net.c [readdir] convert procfs 2013-06-29 12:56:32 +04:00
proc_sysctl.c sysctl: Drop reference added by grab_header in proc_sys_readdir 2017-02-23 03:54:47 +00:00
proc_tty.c proc: use seq_puts()/seq_putc() where possible 2011-01-13 08:03:16 -08:00
root.c proc: prevent stacking filesystems on top 2016-08-22 22:38:27 +01:00
self.c new helper: readlink_copy() 2014-04-01 23:19:15 -04:00
softirqs.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
stat.c genirq: Prevent proc race against freeing of irq descriptors 2015-01-15 10:44:31 +00:00
task_mmu.c pagemap: do not leak physical addresses to non-privileged userspace 2015-03-30 11:11:38 +01:00
task_nommu.c seq_file: remove "%n" usage from seq_file users 2013-11-15 09:32:20 +09:00
uptime.c cputime: Default implementation of nsecs -> cputime conversion 2014-03-13 15:56:43 +01:00
version.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
vmcore.c fs/proc/vmcore.c: remove NULL assignment to static 2014-06-06 16:08:12 -07:00