| From 93362fa47fe98b62e4a34ab408c4a418432e7939 Mon Sep 17 00:00:00 2001 |
| From: Zhou Chengming <zhouchengming1@huawei.com> |
| Date: Fri, 6 Jan 2017 09:32:32 +0800 |
| Subject: sysctl: Drop reference added by grab_header in proc_sys_readdir |
| |
| From: Zhou Chengming <zhouchengming1@huawei.com> |
| |
| commit 93362fa47fe98b62e4a34ab408c4a418432e7939 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: f0c3b5093add ("[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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/proc/proc_sysctl.c | 3 ++- |
| 1 file changed, 2 insertions(+), 1 deletion(-) |
| |
| --- a/fs/proc/proc_sysctl.c |
| +++ b/fs/proc/proc_sysctl.c |
| @@ -703,7 +703,7 @@ static int proc_sys_readdir(struct file |
| ctl_dir = container_of(head, struct ctl_dir, header); |
| |
| if (!dir_emit_dots(file, ctx)) |
| - return 0; |
| + goto out; |
| |
| pos = 2; |
| |
| @@ -713,6 +713,7 @@ static int proc_sys_readdir(struct file |
| break; |
| } |
| } |
| +out: |
| sysctl_head_finish(head); |
| return 0; |
| } |