linux-kernel - [PATCH 3.2 149/164] __ptrace_may_access() should not deny sub-threads

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Message-ID: <lsq.1438473758.832893497@decadent.org.uk>
Date:	Sun, 02 Aug 2015 01:02:38 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Mark Grondona" <mgrondona@...l.gov>,
	"Ben Woodard" <woodard@...hat.com>,
	"Oleg Nesterov" <oleg@...hat.com>,
	"Sheng Yong" <shengyong1@...wei.com>
Subject: [PATCH 3.2 149/164] __ptrace_may_access() should not deny sub-threads

3.2.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Grondona <mgrondona@...l.gov>

commit 73af963f9f3036dffed55c3a2898598186db1045 upstream.

__ptrace_may_access() checks get_dumpable/ptrace_has_cap/etc if task !=
current, this can can lead to surprising results.

For example, a sub-thread can't readlink("/proc/self/exe") if the
executable is not readable.  setup_new_exec()->would_dump() notices that
inode_permission(MAY_READ) fails and then it does
set_dumpable(suid_dumpable).  After that get_dumpable() fails.

(It is not clear why proc_pid_readlink() checks get_dumpable(), perhaps we
could add PTRACE_MODE_NODUMPABLE)

Change __ptrace_may_access() to use same_thread_group() instead of "task
== current".  Any security check is pointless when the tasks share the
same ->mm.

Signed-off-by: Mark Grondona <mgrondona@...l.gov>
Signed-off-by: Ben Woodard <woodard@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Cc: Sheng Yong <shengyong1@...wei.com>
---
 kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -225,7 +225,7 @@ int __ptrace_may_access(struct task_stru
 	 */
 	int dumpable = 0;
 	/* Don't let security modules deny introspection */
-	if (task == current)
+	if (same_thread_group(task, current))
 		return 0;
 	rcu_read_lock();
 	tcred = __task_cred(task);

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