From: Oleg Nesterov <oleg@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>,
Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
Eric Dumazet <edumazet@google.com>,
Jan Kratochvil <jan.kratochvil@redhat.com>,
Julien Tinnes <jln@google.com>, Kees Cook <keescook@google.com>,
Kostya Serebryany <kcc@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
Pedro Alves <palves@redhat.com>,
Robert Swiecki <swiecki@google.com>,
Roland McGrath <roland@hack.frob.com>,
syzkaller@googlegroups.com, linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] wait/ptrace: always assume __WALL if the child is traced
Date: Tue, 20 Oct 2015 19:17:54 +0200 [thread overview]
Message-ID: <20151020171754.GA29304@redhat.com> (raw)
In-Reply-To: <20151020171740.GA29290@redhat.com>
The following program (simplified version of generated by syzkaller)
#include <pthread.h>
#include <unistd.h>
#include <sys/ptrace.h>
#include <stdio.h>
#include <signal.h>
void *thread_func(void *arg)
{
ptrace(PTRACE_TRACEME, 0,0,0);
return 0;
}
int main(void)
{
pthread_t thread;
if (fork())
return 0;
while (getppid() != 1)
;
pthread_create(&thread, NULL, thread_func, NULL);
pthread_join(thread, NULL);
return 0;
}
creates the unreapable zombie if /sbin/init doesn't use __WALL.
This is not a kernel bug, at least in a sense that everything works as
expected: debugger should reap a traced sub-thread before it can reap
the leader, but without __WALL/__WCLONE do_wait() ignores sub-threads.
Unfortunately, it seems that /sbin/init in most (all?) distributions
doesn't use it and we have to change the kernel to avoid the problem.
This patch just adds the "ptrace" check into eligible_child(). To some
degree this matches the "tsk->ptrace" in exit_notify(), ->exit_signal
is mostly ignored when the tracee reports to debugger.
This obviously means the user-visible change: __WCLONE and __WALL no
longer have any meaning for debugger. And I can only hope that this
won't break something.
We could make a more conservative change. Say, we can take __WCLONE
into account, or !thread_group_leader(). But it would be nice to not
complicate these historical/confusing checks.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
---
kernel/exit.c | 29 ++++++++++++++++++++---------
1 files changed, 20 insertions(+), 9 deletions(-)
diff --git a/kernel/exit.c b/kernel/exit.c
index 22fcc05..819f51e 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -914,17 +914,28 @@ static int eligible_pid(struct wait_opts *wo, struct task_struct *p)
task_pid_type(p, wo->wo_type) == wo->wo_pid;
}
-static int eligible_child(struct wait_opts *wo, struct task_struct *p)
+static int
+eligible_child(struct wait_opts *wo, bool ptrace, struct task_struct *p)
{
if (!eligible_pid(wo, p))
return 0;
- /* Wait for all children (clone and not) if __WALL is set;
- * otherwise, wait for clone children *only* if __WCLONE is
- * set; otherwise, wait for non-clone children *only*. (Note:
- * A "clone" child here is one that reports to its parent
- * using a signal other than SIGCHLD.) */
- if (((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
- && !(wo->wo_flags & __WALL))
+
+ /*
+ * Wait for all children (clone and not) if __WALL is set or
+ * if it is traced by us.
+ */
+ if (ptrace || (wo->wo_flags & __WALL))
+ return 1;
+
+ /*
+ * Otherwise, wait for clone children *only* if __WCLONE is set;
+ * otherwise, wait for non-clone children *only*.
+ *
+ * Note: a "clone" child here is one that reports to its parent
+ * using a signal other than SIGCHLD, or a non-leader thread which
+ * we can only see if it is traced by us.
+ */
+ if ((p->exit_signal != SIGCHLD) ^ !!(wo->wo_flags & __WCLONE))
return 0;
return 1;
@@ -1297,7 +1308,7 @@ static int wait_consider_task(struct wait_opts *wo, int ptrace,
if (unlikely(exit_state == EXIT_DEAD))
return 0;
- ret = eligible_child(wo, p);
+ ret = eligible_child(wo, ptrace, p);
if (!ret)
return ret;
--
1.5.5.1
next prev parent reply other threads:[~2015-10-20 17:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-20 17:17 [PATCH 0/2] wait/ptrace: always assume __WALL if the child is traced Oleg Nesterov
2015-10-20 17:17 ` Oleg Nesterov [this message]
2015-10-20 22:31 ` [PATCH 1/2] " Andrew Morton
2015-10-21 3:27 ` Vasily Averin
2015-10-21 17:41 ` Oleg Nesterov
2015-10-21 19:47 ` Andrew Morton
2015-10-21 20:44 ` Oleg Nesterov
2015-10-21 19:59 ` Denys Vlasenko
2015-10-21 20:31 ` Denys Vlasenko
2015-10-21 21:47 ` Oleg Nesterov
2015-10-21 23:27 ` Denys Vlasenko
2015-10-25 15:54 ` Oleg Nesterov
2015-10-26 12:08 ` Pedro Alves
2015-10-28 16:11 ` Oleg Nesterov
2015-10-28 15:43 ` Pedro Alves
2015-10-28 19:02 ` Oleg Nesterov
2015-10-22 13:51 ` Denys Vlasenko
2015-10-20 17:17 ` [PATCH 2/2] wait: allow sys_waitid() to use __WNOTHREAD/__WCLONE/__WALL Oleg Nesterov
2015-10-20 17:36 ` [PATCH 0/2] wait/ptrace: always assume __WALL if the child is traced Oleg Nesterov
2015-10-22 14:40 ` Pedro Alves
2015-10-25 15:42 ` Oleg Nesterov
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