linux-kernel - [PATCH 3.12 163/235] sysctl: Drop reference added by grab_header in proc_sys

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <baa7295e1d686a443c0c23156b0bc9058d783aa4.1485514374.git.jslaby@suse.cz>
Date:   Fri, 27 Jan 2017 11:54:56 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Zhou Chengming <zhouchengming1@...wei.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 163/235] sysctl: Drop reference added by grab_header in proc_sys_readdir

From: Zhou Chengming <zhouchengming1@...wei.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...hat.com>
Tested-by: Yang Shukui <yangshukui@...wei.com>
Signed-off-by: Zhou Chengming <zhouchengming1@...wei.com>
Acked-by: Al Viro <viro@...IV.linux.org.uk>
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 fs/proc/proc_sysctl.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 71290463a1d3..c615a4592572 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -666,7 +666,7 @@ static int proc_sys_readdir(struct file *file, struct dir_context *ctx)
 	ctl_dir = container_of(head, struct ctl_dir, header);
 
 	if (!dir_emit_dots(file, ctx))
-		return 0;
+		goto out;
 
 	pos = 2;
 
@@ -676,6 +676,7 @@ static int proc_sys_readdir(struct file *file, struct dir_context *ctx)
 			break;
 		}
 	}
+out:
 	sysctl_head_finish(head);
 	return 0;
 }
-- 
2.11.0