linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Christian Brauner <christian.brauner@ubuntu.com>
To: christian.brauner@ubuntu.com
Cc: bsingharora@gmail.com, elver@google.com,
	linux-kernel@vger.kernel.org,
	syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com,
	syzkaller-bugs@googlegroups.com,
	Dmitry Vyukov <dvyukov@google.com>
Subject: [PATCH] taskstats: fix data-race
Date: Mon,  7 Oct 2019 01:52:16 +0200	[thread overview]
Message-ID: <20191006235216.7483-1-christian.brauner@ubuntu.com> (raw)
In-Reply-To: <20191005112806.13960-1-christian.brauner@ubuntu.com>

When assiging and testing taskstats in taskstats_exit() there's a race
when writing and reading sig->stats when a thread-group with more than
one thread exits:

cpu0:
thread catches fatal signal and whole thread-group gets taken down
 do_exit()
 do_group_exit()
 taskstats_exit()
 taskstats_tgid_alloc()
The tasks reads sig->stats holding sighand lock seeing garbage.

cpu1:
task calls exit_group()
 do_exit()
 do_group_exit()
 taskstats_exit()
 taskstats_tgid_alloc()
The task takes sighand lock and assigns new stats to sig->stats.

Fix this by using READ_ONCE() and smp_store_release().

Reported-by: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v1 */
Link: https://lore.kernel.org/r/20191005112806.13960-1-christian.brauner@ubuntu.com

/* v2 */
- Dmitry Vyukov <dvyukov@google.com>, Marco Elver <elver@google.com>:
  - fix the original double-checked locking using memory barriers
---
 kernel/taskstats.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 13a0f2e6ebc2..8ee046e8a792 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -554,24 +554,25 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
 static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
 {
 	struct signal_struct *sig = tsk->signal;
-	struct taskstats *stats;
+	struct taskstats *stats_new, *stats;
 
-	if (sig->stats || thread_group_empty(tsk))
-		goto ret;
+	stats = READ_ONCE(sig->stats);
+	if (stats || thread_group_empty(tsk))
+		return stats;
 
 	/* No problem if kmem_cache_zalloc() fails */
-	stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
+	stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
 
 	spin_lock_irq(&tsk->sighand->siglock);
 	if (!sig->stats) {
-		sig->stats = stats;
-		stats = NULL;
+		smp_store_release(&sig->stats, stats_new);
+		stats_new = NULL;
 	}
 	spin_unlock_irq(&tsk->sighand->siglock);
 
-	if (stats)
-		kmem_cache_free(taskstats_cache, stats);
-ret:
+	if (stats_new)
+		kmem_cache_free(taskstats_cache, stats_new);
+
 	return sig->stats;
 }
 
-- 
2.23.0


  parent reply	other threads:[~2019-10-06 23:52 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-05  4:26 KCSAN: data-race in taskstats_exit / taskstats_exit syzbot
2019-10-05  4:29 ` Dmitry Vyukov
2019-10-05 11:29   ` Christian Brauner
2019-10-05 11:28 ` [PATCH] taskstats: fix data-race Christian Brauner
2019-10-05 13:33   ` Marco Elver
2019-10-05 14:15     ` Christian Brauner
2019-10-05 14:34       ` Marco Elver
2019-10-06 10:00   ` Dmitry Vyukov
2019-10-06 10:59     ` Christian Brauner
2019-10-06 23:52   ` Christian Brauner [this message]
2019-10-07  7:31     ` Dmitry Vyukov
2019-10-07  9:29       ` Christian Brauner
2019-10-07 10:40     ` Andrea Parri
2019-10-07 10:50       ` Christian Brauner
2019-10-07 11:01       ` [PATCH v2] " Christian Brauner
2019-10-07 13:18         ` Andrea Parri
2019-10-07 13:28           ` Christian Brauner
2019-10-07 13:50           ` Dmitry Vyukov
2019-10-07 13:55             ` Christian Brauner
2019-10-07 14:08               ` Dmitry Vyukov
2019-10-07 14:10                 ` Christian Brauner
2019-10-07 14:14             ` Andrea Parri
2019-10-07 14:18               ` Dmitry Vyukov
2019-10-08 14:20                 ` Andrea Parri
2019-10-08 14:24                   ` Christian Brauner
2019-10-08 15:26                     ` Andrea Parri
2019-10-08 15:35                       ` Christian Brauner
2019-10-08 15:44                         ` Andrea Parri
2019-10-09 11:31                           ` [PATCH] " Christian Brauner
2019-10-09 11:40                             ` Christian Brauner
2019-10-09 11:48                             ` [PATCH v5] " Christian Brauner
2019-10-09 12:08                               ` Andrea Parri
2019-10-09 13:26                               ` Christian Brauner
2019-10-21 11:33                               ` [PATCH v6] " Christian Brauner
2019-10-21 12:19                                 ` Rasmus Villemoes
2019-10-21 13:04                                   ` Christian Brauner
2019-11-29 17:56                                     ` Will Deacon
2019-11-30 15:08                                       ` Christian Brauner
2019-10-23 12:16                                 ` Andrea Parri
2019-10-23 12:39                                   ` Dmitry Vyukov
2019-10-23 13:11                                     ` Christian Brauner
2019-10-23 13:20                                       ` Dmitry Vyukov
2019-10-24 11:31                                     ` Andrea Parri
2019-10-24 11:51                                       ` Dmitry Vyukov
2019-10-24 13:05                                         ` Andrea Parri
2019-10-24 13:13                                           ` Dmitry Vyukov
2019-10-24 13:21                                             ` Christian Brauner
2019-10-24 13:34                                               ` Dmitry Vyukov
2019-10-24 13:43                                             ` Andrea Parri
2019-10-24 13:58                                               ` Dmitry Vyukov
2019-10-24 14:40                                                 ` Andrea Parri
2019-10-24 14:49                                                   ` Dmitry Vyukov
2019-11-29 17:57                                 ` Will Deacon
2019-10-09 11:48                             ` [PATCH] " Marco Elver
2019-10-09 11:53                               ` Christian Brauner
2019-11-06  0:27   ` Balbir Singh
2019-11-06  0:09 ` KCSAN: data-race in taskstats_exit / taskstats_exit Balbir Singh
2019-11-06 10:23   ` Marco Elver
2019-11-07 10:39     ` Balbir Singh
2019-11-08  0:54     ` Balbir Singh
2019-11-08  8:55       ` Dmitry Vyukov
2019-11-09  3:42         ` Balbir Singh

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=20191006235216.7483-1-christian.brauner@ubuntu.com \
    --to=christian.brauner@ubuntu.com \
    --cc=bsingharora@gmail.com \
    --cc=dvyukov@google.com \
    --cc=elver@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com \
    --cc=syzkaller-bugs@googlegroups.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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).