2017-10-31 13:24:35 -04:00
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From 93362fa47fe98b62e4a34ab408c4a418432e7939 Mon Sep 17 00:00:00 2001
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From: Zhou Chengming <zhouchengming1@huawei.com>
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Date: Fri, 6 Jan 2017 09:32:32 +0800
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Subject: sysctl: Drop reference added by grab_header in proc_sys_readdir
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Fixes CVE-2016-9191, proc_sys_readdir doesn't drop reference
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added by grab_header when return from !dir_emit_dots path.
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It can cause any path called unregister_sysctl_table will
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wait forever.
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The calltrace of CVE-2016-9191:
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[ 5535.960522] Call Trace:
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[ 5535.963265] [<ffffffff817cdaaf>] schedule+0x3f/0xa0
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[ 5535.968817] [<ffffffff817d33fb>] schedule_timeout+0x3db/0x6f0
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[ 5535.975346] [<ffffffff817cf055>] ? wait_for_completion+0x45/0x130
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[ 5535.982256] [<ffffffff817cf0d3>] wait_for_completion+0xc3/0x130
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[ 5535.988972] [<ffffffff810d1fd0>] ? wake_up_q+0x80/0x80
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[ 5535.994804] [<ffffffff8130de64>] drop_sysctl_table+0xc4/0xe0
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[ 5536.001227] [<ffffffff8130de17>] drop_sysctl_table+0x77/0xe0
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[ 5536.007648] [<ffffffff8130decd>] unregister_sysctl_table+0x4d/0xa0
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[ 5536.014654] [<ffffffff8130deff>] unregister_sysctl_table+0x7f/0xa0
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[ 5536.021657] [<ffffffff810f57f5>] unregister_sched_domain_sysctl+0x15/0x40
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[ 5536.029344] [<ffffffff810d7704>] partition_sched_domains+0x44/0x450
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[ 5536.036447] [<ffffffff817d0761>] ? __mutex_unlock_slowpath+0x111/0x1f0
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[ 5536.043844] [<ffffffff81167684>] rebuild_sched_domains_locked+0x64/0xb0
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[ 5536.051336] [<ffffffff8116789d>] update_flag+0x11d/0x210
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[ 5536.057373] [<ffffffff817cf61f>] ? mutex_lock_nested+0x2df/0x450
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[ 5536.064186] [<ffffffff81167acb>] ? cpuset_css_offline+0x1b/0x60
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[ 5536.070899] [<ffffffff810fce3d>] ? trace_hardirqs_on+0xd/0x10
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[ 5536.077420] [<ffffffff817cf61f>] ? mutex_lock_nested+0x2df/0x450
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[ 5536.084234] [<ffffffff8115a9f5>] ? css_killed_work_fn+0x25/0x220
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[ 5536.091049] [<ffffffff81167ae5>] cpuset_css_offline+0x35/0x60
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[ 5536.097571] [<ffffffff8115aa2c>] css_killed_work_fn+0x5c/0x220
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[ 5536.104207] [<ffffffff810bc83f>] process_one_work+0x1df/0x710
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[ 5536.110736] [<ffffffff810bc7c0>] ? process_one_work+0x160/0x710
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[ 5536.117461] [<ffffffff810bce9b>] worker_thread+0x12b/0x4a0
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[ 5536.123697] [<ffffffff810bcd70>] ? process_one_work+0x710/0x710
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[ 5536.130426] [<ffffffff810c3f7e>] kthread+0xfe/0x120
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[ 5536.135991] [<ffffffff817d4baf>] ret_from_fork+0x1f/0x40
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[ 5536.142041] [<ffffffff810c3e80>] ? kthread_create_on_node+0x230/0x230
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One cgroup maintainer mentioned that "cgroup is trying to offline
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a cpuset css, which takes place under cgroup_mutex. The offlining
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ends up trying to drain active usages of a sysctl table which apprently
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is not happening."
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The real reason is that proc_sys_readdir doesn't drop reference added
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by grab_header when return from !dir_emit_dots path. So this cpuset
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offline path will wait here forever.
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See here for details: http://www.openwall.com/lists/oss-security/2016/11/04/13
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Fixes: f0c3b5093add ("[readdir] convert procfs")
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Cc: stable@vger.kernel.org
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Reported-by: CAI Qian <caiqian@redhat.com>
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Tested-by: Yang Shukui <yangshukui@huawei.com>
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Signed-off-by: Zhou Chengming <zhouchengming1@huawei.com>
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Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
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Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
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---
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fs/proc/proc_sysctl.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
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index 55313d9..d4e37ac 100644
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--- a/fs/proc/proc_sysctl.c
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+++ b/fs/proc/proc_sysctl.c
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@@ -709,7 +709,7 @@ static int proc_sys_readdir(struct file *file, struct dir_context *ctx)
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ctl_dir = container_of(head, struct ctl_dir, header);
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if (!dir_emit_dots(file, ctx))
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- return 0;
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+ goto out;
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pos = 2;
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@@ -719,6 +719,7 @@ static int proc_sys_readdir(struct file *file, struct dir_context *ctx)
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break;
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}
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}
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+out:
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sysctl_head_finish(head);
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return 0;
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}
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--
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cgit v1.1
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