From: Eric Dumazet <eric.dumazet@gmail.com>
To: syzbot <syzbot+3ef049d50587836c0606@syzkaller.appspotmail.com>,
elver@google.com, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
viro@zeniv.linux.org.uk,
Linus Torvalds <torvalds@linux-foundation.org>,
Eric Dumazet <edumazet@google.com>
Subject: Re: KCSAN: data-race in __alloc_file / __alloc_file
Date: Fri, 8 Nov 2019 05:28:02 -0800 [thread overview]
Message-ID: <6bddae34-93df-6820-0390-ac18dcbf0927@gmail.com> (raw)
In-Reply-To: <000000000000c422a80596d595ee@google.com>
On 11/8/19 5:16 AM, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 05f22368 x86, kcsan: Enable KCSAN for x86
> git tree: https://github.com/google/ktsan.git kcsan
> console output: https://syzkaller.appspot.com/x/log.txt?x=10d7fd88e00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=87d111955f40591f
> dashboard link: https://syzkaller.appspot.com/bug?extid=3ef049d50587836c0606
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+3ef049d50587836c0606@syzkaller.appspotmail.com
>
> ==================================================================
> BUG: KCSAN: data-race in __alloc_file / __alloc_file
>
> write to 0xffff8880bb157398 of 4 bytes by task 10993 on cpu 0:
> get_cred include/linux/cred.h:253 [inline]
> __alloc_file+0x74/0x210 fs/file_table.c:105
> alloc_empty_file+0x8f/0x180 fs/file_table.c:151
> alloc_file+0x4e/0x2b0 fs/file_table.c:193
> alloc_file_pseudo+0x11c/0x1b0 fs/file_table.c:232
> anon_inode_getfile fs/anon_inodes.c:91 [inline]
> anon_inode_getfile+0x103/0x1d0 fs/anon_inodes.c:74
> __do_sys_perf_event_open+0xd32/0x1ac0 kernel/events/core.c:11100
> __se_sys_perf_event_open kernel/events/core.c:10867 [inline]
> __x64_sys_perf_event_open+0x70/0x90 kernel/events/core.c:10867
> do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> write to 0xffff8880bb157398 of 4 bytes by task 11004 on cpu 1:
> get_cred include/linux/cred.h:253 [inline]
> __alloc_file+0x74/0x210 fs/file_table.c:105
> alloc_empty_file+0x8f/0x180 fs/file_table.c:151
> path_openat+0x74/0x36e0 fs/namei.c:3514
> do_filp_open+0x11e/0x1b0 fs/namei.c:3555
> do_sys_open+0x3b3/0x4f0 fs/open.c:1097
> __do_sys_open fs/open.c:1115 [inline]
> __se_sys_open fs/open.c:1110 [inline]
> __x64_sys_open+0x55/0x70 fs/open.c:1110
> do_syscall_64+0xcc/0x370 arch/x86/entry/common.c:290
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 1 PID: 11004 Comm: syz-executor.5 Not tainted 5.4.0-rc3+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> ==================================================================
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
Linus, what do you think of the following fix ?
I also took the opportunity avoiding dirtying a cache line if this was possible.
diff --git a/include/linux/cred.h b/include/linux/cred.h
index 18639c069263fbe79dfd5a36163c656dca5da220..01b5b7d4e054ddca0df676dc1ceb068e5d71a3f8 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -250,7 +250,14 @@ static inline const struct cred *get_cred(const struct cred *cred)
if (!cred)
return cred;
validate_creds(cred);
- nonconst_cred->non_rcu = 0;
+
+ /*
+ * Avoid dirtying one cache line. The WRITE_ONCE() also pairs
+ * with itself, since we run without protection of a lock.
+ */
+ if (READ_ONCE(nonconst_cred->non_rcu))
+ WRITE_ONCE(nonconst_cred->non_rcu, 0);
+
return get_new_cred(nonconst_cred);
}
@@ -262,7 +269,14 @@ static inline const struct cred *get_cred_rcu(const struct cred *cred)
if (!atomic_inc_not_zero(&nonconst_cred->usage))
return NULL;
validate_creds(cred);
- nonconst_cred->non_rcu = 0;
+
+ /*
+ * Avoid dirtying one cache line. The WRITE_ONCE() also pairs
+ * with itself, since we run without protection of a lock.
+ */
+ if (READ_ONCE(nonconst_cred->non_rcu))
+ WRITE_ONCE(nonconst_cred->non_rcu, 0);
+
return cred;
}
next prev parent reply other threads:[~2019-11-08 13:28 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 13:16 KCSAN: data-race in __alloc_file / __alloc_file syzbot
2019-11-08 13:28 ` Eric Dumazet [this message]
2019-11-08 17:01 ` Linus Torvalds
2019-11-08 17:22 ` Eric Dumazet
2019-11-08 17:38 ` Linus Torvalds
2019-11-08 17:53 ` Eric Dumazet
2019-11-08 17:55 ` Eric Dumazet
2019-11-08 18:02 ` Eric Dumazet
2019-11-08 18:12 ` Linus Torvalds
2019-11-08 20:30 ` Linus Torvalds
2019-11-08 20:53 ` Eric Dumazet
2019-11-08 21:36 ` Linus Torvalds
2019-11-08 18:05 ` Linus Torvalds
2019-11-08 18:15 ` Marco Elver
2019-11-08 18:40 ` Linus Torvalds
2019-11-08 19:48 ` Marco Elver
2019-11-08 20:26 ` Linus Torvalds
2019-11-08 21:57 ` Alan Stern
2019-11-08 22:06 ` Linus Torvalds
2019-11-09 23:08 ` Alan Stern
[not found] <CAHk-=wjB61GNmqpX0BLA5tpL4tsjWV7akaTc2Roth7uGgax+mw@mail.gmail.com>
2019-11-10 16:09 ` Alan Stern
2019-11-10 19:10 ` Marco Elver
2019-11-11 15:51 ` Alan Stern
2019-11-11 16:51 ` Linus Torvalds
2019-11-11 17:52 ` Eric Dumazet
2019-11-11 18:04 ` Linus Torvalds
2019-11-11 18:31 ` Eric Dumazet
2019-11-11 18:44 ` Eric Dumazet
2019-11-11 19:00 ` Linus Torvalds
2019-11-11 19:13 ` Eric Dumazet
2019-11-11 20:43 ` Linus Torvalds
2019-11-11 20:46 ` Linus Torvalds
2019-11-11 21:53 ` Eric Dumazet
2019-11-11 23:51 ` Linus Torvalds
2019-11-12 16:50 ` Kirill Smelkov
2019-11-12 17:23 ` Linus Torvalds
2019-11-12 17:36 ` Linus Torvalds
2019-11-17 18:56 ` Kirill Smelkov
2019-11-17 19:20 ` Linus Torvalds
2019-11-11 18:50 ` Linus Torvalds
2019-11-11 18:59 ` Marco Elver
2019-11-11 18:59 ` Eric Dumazet
2019-11-10 19:12 ` Linus Torvalds
2019-11-10 19:20 ` Linus Torvalds
2019-11-10 20:44 ` Paul E. McKenney
2019-11-10 21:10 ` Linus Torvalds
2019-11-10 21:31 ` Paul E. McKenney
2019-11-11 14:17 ` Marco Elver
2019-11-11 14:31 ` Paul E. McKenney
2019-11-11 15:10 ` Marco Elver
2019-11-13 0:25 ` Paul E. McKenney
2019-11-12 19:14 ` Alan Stern
2019-11-12 19:47 ` Linus Torvalds
2019-11-12 20:29 ` Alan Stern
2019-11-12 20:58 ` Linus Torvalds
2019-11-12 21:13 ` Linus Torvalds
2019-11-12 22:05 ` Marco Elver
2019-11-12 21:48 ` Alan Stern
2019-11-12 22:07 ` Eric Dumazet
2019-11-12 22:44 ` Alexei Starovoitov
2019-11-12 23:17 ` Eric Dumazet
2019-11-12 23:40 ` Linus Torvalds
2019-11-13 15:00 ` Marco Elver
2019-11-13 16:57 ` Linus Torvalds
2019-11-13 21:33 ` Marco Elver
2019-11-13 21:50 ` Alan Stern
2019-11-13 22:48 ` Marco Elver
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