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From: Jann Horn <jann@thejh.net>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
	Roland McGrath <roland@hack.frob.com>,
	Oleg Nesterov <oleg@redhat.com>,
	John Johansen <john.johansen@canonical.com>,
	James Morris <james.l.morris@oracle.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Paul Moore <aul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Kees Cook <eescook@chromium.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Janis Danisevskis <jdanis@google.com>,
	Seth Forshee <seth.forshee@canonical.com>,
	"Eric . Biederman" <ebiederm@xmission.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Benjamin LaHaise <bcrl@kvack.org>
Cc: linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, security@kernel.org
Subject: [PATCH 4/9] futex: don't leak robust_list pointer
Date: Sun, 18 Sep 2016 17:05:12 +0200	[thread overview]
Message-ID: <1474211117-16674-5-git-send-email-jann@thejh.net> (raw)
In-Reply-To: <1474211117-16674-1-git-send-email-jann@thejh.net>

This prevents an attacker from determining the robust_list or
compat_robust_list userspace pointer of a process created by executing
a setuid binary. Such an attack could be performed by racing
get_robust_list() with a setuid execution. The impact of this issue is that
an attacker could theoretically bypass ASLR when attacking setuid binaries.

Signed-off-by: Jann Horn <jann@thejh.net>
---
 kernel/futex.c        | 31 +++++++++++++++++++++----------
 kernel/futex_compat.c | 31 +++++++++++++++++++++----------
 2 files changed, 42 insertions(+), 20 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 46cb3a3..002f056 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3007,31 +3007,42 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
 	if (!futex_cmpxchg_enabled)
 		return -ENOSYS;
 
-	rcu_read_lock();
-
-	ret = -ESRCH;
-	if (!pid)
+	if (!pid) {
 		p = current;
-	else {
+		get_task_struct(p);
+	} else {
+		rcu_read_lock();
 		p = find_task_by_vpid(pid);
-		if (!p)
-			goto err_unlock;
+		/* pin the task to permit dropping the RCU read lock before
+		 * acquiring the mutex
+		 */
+		get_task_struct(p);
+		rcu_read_unlock();
 	}
+	if (!p)
+		return -ESRCH;
+
+	ret = mutex_lock_killable(&p->signal->cred_guard_light);
+	if (ret)
+		goto err_put;
 
 	ret = -EPERM;
 	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
 		goto err_unlock;
 
 	head = p->robust_list;
-	rcu_read_unlock();
+
+	mutex_unlock(&p->signal->cred_guard_light);
+	put_task_struct(p);
 
 	if (put_user(sizeof(*head), len_ptr))
 		return -EFAULT;
 	return put_user(head, head_ptr);
 
 err_unlock:
-	rcu_read_unlock();
-
+	mutex_unlock(&current->signal->cred_guard_light);
+err_put:
+	put_task_struct(p);
 	return ret;
 }
 
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 4ae3232..241b4a9 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -143,31 +143,42 @@ COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
 	if (!futex_cmpxchg_enabled)
 		return -ENOSYS;
 
-	rcu_read_lock();
-
-	ret = -ESRCH;
-	if (!pid)
+	if (!pid) {
 		p = current;
-	else {
+		get_task_struct(p);
+	} else {
+		rcu_read_lock();
 		p = find_task_by_vpid(pid);
-		if (!p)
-			goto err_unlock;
+		/* pin the task to permit dropping the RCU read lock before
+		 * acquiring the mutex
+		 */
+		get_task_struct(p);
+		rcu_read_unlock();
 	}
+	if (!p)
+		return -ESRCH;
+
+	ret = mutex_lock_killable(&p->signal->cred_guard_light);
+	if (ret)
+		goto err_put;
 
 	ret = -EPERM;
 	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
 		goto err_unlock;
 
 	head = p->compat_robust_list;
-	rcu_read_unlock();
+
+	mutex_unlock(&p->signal->cred_guard_light);
+	put_task_struct(p);
 
 	if (put_user(sizeof(*head), len_ptr))
 		return -EFAULT;
 	return put_user(ptr_to_compat(head), head_ptr);
 
 err_unlock:
-	rcu_read_unlock();
-
+	mutex_unlock(&current->signal->cred_guard_light);
+err_put:
+	put_task_struct(p);
 	return ret;
 }
 
-- 
2.1.4


  parent reply	other threads:[~2016-09-18 15:05 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-18 15:05 [PATCH 0/9] Various fixes related to ptrace_may_access() Jann Horn
2016-09-18 15:05 ` [PATCH 1/9] exec: introduce cred_guard_light Jann Horn
2016-09-18 15:05 ` [PATCH 2/9] exec: turn self_exec_id into self_privunit_id Jann Horn
2016-09-18 18:13   ` Ben Hutchings
2016-09-18 18:31     ` Jann Horn
2016-09-18 18:45       ` Ben Hutchings
2016-09-18 19:08         ` Jann Horn
2016-09-18 19:57         ` Andy Lutomirski
2016-09-19 15:31           ` Jann Horn
2016-09-18 15:05 ` [PATCH 3/9] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-19 13:01   ` Stephen Smalley
2016-09-19 14:32     ` Jann Horn
2016-09-19 14:45       ` Stephen Smalley
2016-09-18 15:05 ` Jann Horn [this message]
2016-09-18 18:28   ` [PATCH 4/9] futex: don't leak robust_list pointer Ben Hutchings
2016-09-18 18:33     ` Jann Horn
2016-09-18 15:05 ` [PATCH 5/9] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-18 19:15   ` Jann Horn
2016-09-18 15:05 ` [PATCH 6/9] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-18 15:05 ` [PATCH 7/9] ptrace: forbid ptrace checks against current_cred() from VFS context Jann Horn
2016-09-18 18:38   ` Ben Hutchings
2016-09-18 18:40     ` Jann Horn
2016-09-18 19:57   ` Andy Lutomirski
2016-09-18 20:38     ` Jann Horn
2016-09-18 20:18   ` Linus Torvalds
2016-09-18 20:52     ` Jann Horn
2016-09-18 15:05 ` [PATCH 8/9] fs/proc: fix attr access check Jann Horn
2016-09-18 15:05 ` [PATCH 9/9] Documentation: add security/ptrace_checks.txt Jann Horn

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