From: Jann Horn <jann@thejh.net>
To: Ben Hutchings <ben@decadent.org.uk>
Cc: 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>,
linux-fsdevel@vger.kernel.org,
linux-security-module@vger.kernel.org, security@kernel.org
Subject: Re: [PATCH 4/9] futex: don't leak robust_list pointer
Date: Sun, 18 Sep 2016 20:33:42 +0200 [thread overview]
Message-ID: <20160918183342.GB17170@pc.thejh.net> (raw)
In-Reply-To: <20160918182846.GR10601@decadent.org.uk>
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On Sun, Sep 18, 2016 at 07:28:46PM +0100, Ben Hutchings wrote:
> On Sun, Sep 18, 2016 at 05:05:12PM +0200, Jann Horn wrote:
> > 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);
>
> get_task_struct() requires a non-null pointer so you can't move the
> null check below it.
Oh, right, thanks. Will fix that in v2.
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next prev parent reply other threads:[~2016-09-18 18:33 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 ` [PATCH 4/9] futex: don't leak robust_list pointer Jann Horn
2016-09-18 18:28 ` Ben Hutchings
2016-09-18 18:33 ` Jann Horn [this message]
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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