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Commit bdbb776f authored by Kees Cook's avatar Kees Cook Committed by Thomas Gleixner
Browse files

futex: Do not leak robust list to unprivileged process 



It was possible to extract the robust list head address from a setuid
process if it had used set_robust_list(), allowing an ASLR info leak. This
changes the permission checks to be the same as those used for similar
info that comes out of /proc.

Running a setuid program that uses robust futexes would have had:
  cred->euid != pcred->euid
  cred->euid == pcred->uid
so the old permissions check would allow it. I'm not aware of any setuid
programs that use robust futexes, so this is just a preventative measure.

(This patch is based on changes from grsecurity.)

Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Darren Hart <dvhart@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: kernel-hardening@lists.openwall.com
Cc: spender@grsecurity.net
Link: http://lkml.kernel.org/r/20120319231253.GA20893@www.outflux.net


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent b5174fa3

kernel/futex.c

+13 −23
Original line number Diff line number Diff line
@@ -59,6 +59,7 @@ 
#include <linux/magic.h>

#include <linux/pid.h>

#include <linux/nsproxy.h>

#include <linux/ptrace.h>



#include <asm/futex.h>
@@ -2443,39 +2444,28 @@ SYSCALL_DEFINE3(get_robust_list, int, pid, 
{

	struct robust_list_head __user *head;

	unsigned long ret;

	const struct cred *cred = current_cred(), *pcred;

	struct task_struct *p;



	if (!futex_cmpxchg_enabled)

		return -ENOSYS;



	if (!pid)

		head = current->robust_list;

	else {

		struct task_struct *p;

	rcu_read_lock();



	ret = -ESRCH;

		rcu_read_lock();

	if (!pid)

		p = current;

	else {

		p = find_task_by_vpid(pid);

		if (!p)

			goto err_unlock;

		ret = -EPERM;

		pcred = __task_cred(p);

		/* If victim is in different user_ns, then uids are not

		   comparable, so we must have CAP_SYS_PTRACE */

		if (cred->user->user_ns != pcred->user->user_ns) {

			if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))

				goto err_unlock;

			goto ok;

	}

		/* If victim is in same user_ns, then uids are comparable */

		if (cred->euid != pcred->euid &&

		    cred->euid != pcred->uid &&

		    !ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))



	ret = -EPERM;

	if (!ptrace_may_access(p, PTRACE_MODE_READ))

		goto err_unlock;

ok:



	head = p->robust_list;

	rcu_read_unlock();

	}



	if (put_user(sizeof(*head), len_ptr))

		return -EFAULT;

kernel/futex_compat.c

+13 −23
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/compat.h>

#include <linux/nsproxy.h>

#include <linux/futex.h>

#include <linux/ptrace.h>



#include <asm/uaccess.h>
@@ -136,39 +137,28 @@ compat_sys_get_robust_list(int pid, compat_uptr_t __user *head_ptr, 
{

	struct compat_robust_list_head __user *head;

	unsigned long ret;

	const struct cred *cred = current_cred(), *pcred;

	struct task_struct *p;



	if (!futex_cmpxchg_enabled)

		return -ENOSYS;



	if (!pid)

		head = current->compat_robust_list;

	else {

		struct task_struct *p;

	rcu_read_lock();



	ret = -ESRCH;

		rcu_read_lock();

	if (!pid)

		p = current;

	else {

		p = find_task_by_vpid(pid);

		if (!p)

			goto err_unlock;

		ret = -EPERM;

		pcred = __task_cred(p);

		/* If victim is in different user_ns, then uids are not

		   comparable, so we must have CAP_SYS_PTRACE */

		if (cred->user->user_ns != pcred->user->user_ns) {

			if (!ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))

				goto err_unlock;

			goto ok;

	}

		/* If victim is in same user_ns, then uids are comparable */

		if (cred->euid != pcred->euid &&

		    cred->euid != pcred->uid &&

		    !ns_capable(pcred->user->user_ns, CAP_SYS_PTRACE))



	ret = -EPERM;

	if (!ptrace_may_access(p, PTRACE_MODE_READ))

		goto err_unlock;

ok:



	head = p->compat_robust_list;

	rcu_read_unlock();

	}



	if (put_user(sizeof(*head), len_ptr))

		return -EFAULT;