From: Christian Brauner <christian.brauner@ubuntu.com>
To: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com
Cc: bsingharora@gmail.com, elver@google.com,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
Christian Brauner <christian.brauner@ubuntu.com>
Subject: [PATCH] taskstats: fix data-race
Date: Sat, 5 Oct 2019 13:28:06 +0200 [thread overview]
Message-ID: <20191005112806.13960-1-christian.brauner@ubuntu.com> (raw)
In-Reply-To: <0000000000009b403005942237bf@google.com>
When assiging and testing taskstats in taskstats
taskstats_exit() there's a race around writing and reading sig->stats.
cpu0:
task calls exit()
do_exit()
-> taskstats_exit()
-> taskstats_tgid_alloc()
The task takes sighand lock and assigns new stats to sig->stats.
cpu1:
task catches signal
do_exit()
-> taskstats_tgid_alloc()
-> taskstats_exit()
The tasks reads sig->stats __without__ holding sighand lock seeing
garbage.
Fix this by taking sighand lock when reading sig->stats.
Reported-by: syzbot+c5d03165a1bd1dead0c1@syzkaller.appspotmail.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
kernel/taskstats.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 13a0f2e6ebc2..58b145234c4a 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -553,26 +553,32 @@ static int taskstats_user_cmd(struct sk_buff *skb, struct genl_info *info)
static struct taskstats *taskstats_tgid_alloc(struct task_struct *tsk)
{
+ int empty;
+ struct taskstats *stats_new, *stats = NULL;
struct signal_struct *sig = tsk->signal;
- struct taskstats *stats;
-
- if (sig->stats || thread_group_empty(tsk))
- goto ret;
/* No problem if kmem_cache_zalloc() fails */
- stats = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
+ stats_new = kmem_cache_zalloc(taskstats_cache, GFP_KERNEL);
+
+ empty = thread_group_empty(tsk);
spin_lock_irq(&tsk->sighand->siglock);
+ if (sig->stats || empty) {
+ stats = sig->stats;
+ spin_unlock_irq(&tsk->sighand->siglock);
+ goto free_cache;
+ }
+
if (!sig->stats) {
- sig->stats = stats;
- stats = NULL;
+ sig->stats = stats_new;
+ spin_unlock_irq(&tsk->sighand->siglock);
+ return stats_new;
}
spin_unlock_irq(&tsk->sighand->siglock);
- if (stats)
- kmem_cache_free(taskstats_cache, stats);
-ret:
- return sig->stats;
+free_cache:
+ kmem_cache_free(taskstats_cache, stats_new);
+ return stats;
}
/* Send pid data out on exit */
--
2.23.0
next prev parent reply other threads:[~2019-10-05 11:28 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 ` Christian Brauner [this message]
2019-10-05 13:33 ` [PATCH] taskstats: fix data-race 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
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
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