From: Oleg Nesterov <oleg@redhat.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Aleksa Sarai <asarai@suse.com>,
Andy Lutomirski <luto@amacapital.net>,
Attila Fazekas <afazekas@redhat.com>, Jann Horn <jann@thejh.net>,
Kees Cook <keescook@chromium.org>,
Michal Hocko <mhocko@kernel.org>,
Ulrich Obergfell <uobergfe@redhat.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org
Subject: Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped
Date: Sun, 2 Apr 2017 17:35:17 +0200 [thread overview]
Message-ID: <20170402153517.GA12637@redhat.com> (raw)
In-Reply-To: <87vaqooggs.fsf_-_@xmission.com>
On 04/01, Eric W. Biederman wrote:
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1052,6 +1052,7 @@ static int de_thread(struct task_struct *tsk)
> struct signal_struct *sig = tsk->signal;
> struct sighand_struct *oldsighand = tsk->sighand;
> spinlock_t *lock = &oldsighand->siglock;
> + bool may_hang;
>
> if (thread_group_empty(tsk))
> goto no_thread_group;
> @@ -1069,9 +1070,10 @@ static int de_thread(struct task_struct *tsk)
> return -EAGAIN;
> }
>
> + may_hang = atomic_read(&oldsighand->count) != 1;
> sig->group_exit_task = tsk;
> - sig->notify_count = zap_other_threads(tsk);
> - if (!thread_group_leader(tsk))
> + sig->notify_count = zap_other_threads(tsk, may_hang ? 1 : -1);
Eric, this is amazing. So with this patch exec does different things depening
on whether sighand is shared with another CLONE_SIGHAND task or not. To me
this doesn't look sane in any case.
And of course you do realize that it doesn't solve the problem entirely? If I
modify my test-case a little bit
int xxx(void *arg)
{
for (;;)
pause();
}
void *thread(void *arg)
{
ptrace(PTRACE_TRACEME, 0,0,0);
return NULL;
}
int main(void)
{
int pid = fork();
if (!pid) {
pthread_t pt;
char stack[16 * 1024];
clone(xxx, stack + 16*1024, CLONE_SIGHAND|CLONE_VM, NULL);
pthread_create(&pt, NULL, thread, NULL);
pthread_join(pt, NULL);
execlp("echo", "echo", "passed", NULL);
}
sleep(1);
// or anything else which needs ->cred_guard_mutex,
// say open(/proc/$pid/mem)
ptrace(PTRACE_ATTACH, pid, 0,0);
kill(pid, SIGCONT);
return 0;
}
it should deadlock the same way?
So what is the point to make the, well imo insane, patch if it doesn't solve
the problem?
And btw zap_other_threads(may_hang == 0) is racy. Either you need tasklist or
exit_notify() should set tsk->exit_state under siglock, otherwise zap() can
return the wrong count.
Finally. This patch creates the nice security hole. Let me modify my test-case
again:
void *thread(void *arg)
{
ptrace(PTRACE_TRACEME, 0,0,0);
return NULL;
}
int main(void)
{
int pid = fork();
if (!pid) {
pthread_t pt;
pthread_create(&pt, NULL, thread, NULL);
pthread_join(pt, NULL);
execlp(path-to-setuid-binary, args);
}
sleep(1);
// Now we can send the signals to setiuid app
kill(pid+1, ANYSIGNAL);
return 0;
}
I see another email from your with another proposal. I disagree, will reply soon.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: "Eric W. Biederman" <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
Cc: Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
Aleksa Sarai <asarai-IBi9RG/b67k@public.gmane.org>,
Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>,
Attila Fazekas <afazekas-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Jann Horn <jann-XZ1E9jl8jIdeoWH0uzbU5w@public.gmane.org>,
Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
Ulrich Obergfell
<uobergfe-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped
Date: Sun, 2 Apr 2017 17:35:17 +0200 [thread overview]
Message-ID: <20170402153517.GA12637@redhat.com> (raw)
In-Reply-To: <87vaqooggs.fsf_-_-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
On 04/01, Eric W. Biederman wrote:
>
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1052,6 +1052,7 @@ static int de_thread(struct task_struct *tsk)
> struct signal_struct *sig = tsk->signal;
> struct sighand_struct *oldsighand = tsk->sighand;
> spinlock_t *lock = &oldsighand->siglock;
> + bool may_hang;
>
> if (thread_group_empty(tsk))
> goto no_thread_group;
> @@ -1069,9 +1070,10 @@ static int de_thread(struct task_struct *tsk)
> return -EAGAIN;
> }
>
> + may_hang = atomic_read(&oldsighand->count) != 1;
> sig->group_exit_task = tsk;
> - sig->notify_count = zap_other_threads(tsk);
> - if (!thread_group_leader(tsk))
> + sig->notify_count = zap_other_threads(tsk, may_hang ? 1 : -1);
Eric, this is amazing. So with this patch exec does different things depening
on whether sighand is shared with another CLONE_SIGHAND task or not. To me
this doesn't look sane in any case.
And of course you do realize that it doesn't solve the problem entirely? If I
modify my test-case a little bit
int xxx(void *arg)
{
for (;;)
pause();
}
void *thread(void *arg)
{
ptrace(PTRACE_TRACEME, 0,0,0);
return NULL;
}
int main(void)
{
int pid = fork();
if (!pid) {
pthread_t pt;
char stack[16 * 1024];
clone(xxx, stack + 16*1024, CLONE_SIGHAND|CLONE_VM, NULL);
pthread_create(&pt, NULL, thread, NULL);
pthread_join(pt, NULL);
execlp("echo", "echo", "passed", NULL);
}
sleep(1);
// or anything else which needs ->cred_guard_mutex,
// say open(/proc/$pid/mem)
ptrace(PTRACE_ATTACH, pid, 0,0);
kill(pid, SIGCONT);
return 0;
}
it should deadlock the same way?
So what is the point to make the, well imo insane, patch if it doesn't solve
the problem?
And btw zap_other_threads(may_hang == 0) is racy. Either you need tasklist or
exit_notify() should set tsk->exit_state under siglock, otherwise zap() can
return the wrong count.
Finally. This patch creates the nice security hole. Let me modify my test-case
again:
void *thread(void *arg)
{
ptrace(PTRACE_TRACEME, 0,0,0);
return NULL;
}
int main(void)
{
int pid = fork();
if (!pid) {
pthread_t pt;
pthread_create(&pt, NULL, thread, NULL);
pthread_join(pt, NULL);
execlp(path-to-setuid-binary, args);
}
sleep(1);
// Now we can send the signals to setiuid app
kill(pid+1, ANYSIGNAL);
return 0;
}
I see another email from your with another proposal. I disagree, will reply soon.
Oleg.
next prev parent reply other threads:[~2017-04-02 15:35 UTC|newest]
Thread overview: 93+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-13 14:14 [PATCH 0/2] fix the traced mt-exec deadlock Oleg Nesterov
2017-02-13 14:15 ` [PATCH 1/2] exec: don't wait for zombie threads with cred_guard_mutex held Oleg Nesterov
2017-02-13 16:12 ` kbuild test robot
2017-02-13 16:47 ` Oleg Nesterov
2017-02-13 16:39 ` kbuild test robot
2017-02-13 17:27 ` Mika Penttilä
2017-02-13 18:01 ` Oleg Nesterov
2017-02-13 18:04 ` [PATCH V2 " Oleg Nesterov
2017-02-16 11:42 ` Eric W. Biederman
2017-02-20 15:22 ` Oleg Nesterov
2017-02-20 15:36 ` Oleg Nesterov
2017-02-20 22:30 ` Eric W. Biederman
2017-02-21 17:53 ` Oleg Nesterov
2017-02-21 20:20 ` Eric W. Biederman
2017-02-22 17:41 ` Oleg Nesterov
2017-02-17 4:42 ` Eric W. Biederman
2017-02-20 15:50 ` Oleg Nesterov
2017-02-13 14:15 ` [PATCH 2/2] ptrace: ensure PTRACE_EVENT_EXIT won't stop if the tracee is killed by exec Oleg Nesterov
2017-02-24 16:03 ` [PATCH 0/2] fix the traced mt-exec deadlock Oleg Nesterov
2017-03-03 1:05 ` Eric W. Biederman
2017-03-03 17:33 ` Oleg Nesterov
2017-03-03 18:23 ` Eric W. Biederman
2017-03-03 18:23 ` Eric W. Biederman
2017-03-03 18:59 ` Eric W. Biederman
2017-03-03 18:59 ` Eric W. Biederman
2017-03-03 20:06 ` Eric W. Biederman
2017-03-03 20:06 ` Eric W. Biederman
2017-03-03 20:11 ` [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped Eric W. Biederman
2017-03-03 20:11 ` Eric W. Biederman
2017-03-04 17:03 ` Oleg Nesterov
2017-03-30 8:07 ` Eric W. Biederman
2017-04-01 5:11 ` [RFC][PATCH 0/2] exec: Fixing ptrace'd mulit-threaded hang Eric W. Biederman
2017-04-01 5:11 ` Eric W. Biederman
2017-04-01 5:14 ` [RFC][PATCH 1/2] sighand: Count each thread group once in sighand_struct Eric W. Biederman
2017-04-01 5:14 ` Eric W. Biederman
2017-04-01 5:16 ` [RFC][PATCH 2/2] exec: If possible don't wait for ptraced threads to be reaped Eric W. Biederman
2017-04-01 5:16 ` Eric W. Biederman
2017-04-02 15:35 ` Oleg Nesterov [this message]
2017-04-02 15:35 ` Oleg Nesterov
2017-04-02 18:53 ` Eric W. Biederman
2017-04-02 18:53 ` Eric W. Biederman
2017-04-03 18:12 ` Oleg Nesterov
2017-04-03 18:12 ` Oleg Nesterov
2017-04-03 21:04 ` Eric W. Biederman
2017-04-05 16:44 ` Oleg Nesterov
2017-04-02 15:38 ` [RFC][PATCH 0/2] exec: Fixing ptrace'd mulit-threaded hang Oleg Nesterov
2017-04-02 15:38 ` Oleg Nesterov
2017-04-02 22:50 ` [RFC][PATCH v2 0/5] " Eric W. Biederman
2017-04-02 22:50 ` Eric W. Biederman
2017-04-02 22:51 ` [RFC][PATCH v2 1/5] ptrace: Don't wait in PTRACE_O_TRACEEXIT for exec or coredump Eric W. Biederman
2017-04-02 22:51 ` Eric W. Biederman
2017-04-05 16:19 ` Oleg Nesterov
2017-04-02 22:51 ` [RFC][PATCH v2 2/5] sighand: Count each thread group once in sighand_struct Eric W. Biederman
2017-04-02 22:51 ` Eric W. Biederman
2017-04-02 22:52 ` [RFC][PATCH v2 3/5] clone: Disallown CLONE_THREAD with a shared sighand_struct Eric W. Biederman
2017-04-02 22:52 ` Eric W. Biederman
2017-04-05 16:24 ` Oleg Nesterov
2017-04-05 16:24 ` Oleg Nesterov
2017-04-05 17:34 ` Eric W. Biederman
2017-04-05 18:11 ` Oleg Nesterov
2017-04-02 22:53 ` [RFC][PATCH v2 4/5] exec: If possible don't wait for ptraced threads to be reaped Eric W. Biederman
2017-04-02 22:53 ` Eric W. Biederman
2017-04-05 16:15 ` Oleg Nesterov
2017-04-02 22:57 ` [RFC][PATCH v2 5/5] signal: Don't allow accessing signal_struct by old threads after exec Eric W. Biederman
2017-04-02 22:57 ` Eric W. Biederman
2017-04-05 16:18 ` Oleg Nesterov
2017-04-05 16:18 ` Oleg Nesterov
2017-04-05 18:16 ` Eric W. Biederman
2017-04-05 18:16 ` Eric W. Biederman
2017-04-06 15:48 ` Oleg Nesterov
2017-04-06 15:48 ` Oleg Nesterov
2017-04-02 16:15 ` [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped Oleg Nesterov
2017-04-02 16:15 ` Oleg Nesterov
2017-04-02 21:07 ` Eric W. Biederman
2017-04-02 21:07 ` Eric W. Biederman
2017-04-03 18:37 ` Oleg Nesterov
2017-04-03 18:37 ` Oleg Nesterov
2017-04-03 22:49 ` Eric W. Biederman
2017-04-03 22:49 ` Eric W. Biederman
2017-04-03 22:49 ` scope of cred_guard_mutex Eric W. Biederman
2017-04-03 22:49 ` Eric W. Biederman
2017-04-05 16:08 ` Oleg Nesterov
2017-04-05 16:11 ` Kees Cook
2017-04-05 17:53 ` Eric W. Biederman
2017-04-05 18:15 ` Oleg Nesterov
2017-04-06 15:55 ` Oleg Nesterov
2017-04-06 15:55 ` Oleg Nesterov
2017-04-07 22:07 ` Kees Cook
2017-04-07 22:07 ` Kees Cook
2017-09-04 3:19 ` [RFC][PATCH] exec: Don't wait for ptraced threads to be reaped Robert O'Callahan
2017-09-04 3:19 ` Robert O'Callahan
2017-03-04 16:54 ` [PATCH 0/2] fix the traced mt-exec deadlock Oleg Nesterov
2017-03-04 16:54 ` Oleg Nesterov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170402153517.GA12637@redhat.com \
--to=oleg@redhat.com \
--cc=afazekas@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=asarai@suse.com \
--cc=ebiederm@xmission.com \
--cc=jann@thejh.net \
--cc=keescook@chromium.org \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=mhocko@kernel.org \
--cc=uobergfe@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.