[Ocfs2-devel] [BUG] ocfs2/dlm: possible data races in dlm_drop_lockres_ref_done() and dlm_get_lock_resource() - Tuo Li via Ocfs2-devel

From: Tuo Li via Ocfs2-devel <ocfs2-devel@oss.oracle.com>
To: mark@fasheh.com, jlbec@evilplan.org,
	Joseph Qi <joseph.qi@linux.alibaba.com>,
	akpm@linux-foundation.org
Cc: baijiaju1990@outlook.com,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	ocfs2-devel@oss.oracle.com
Subject: [Ocfs2-devel] [BUG] ocfs2/dlm: possible data races in dlm_drop_lockres_ref_done() and dlm_get_lock_resource()
Date: Tue, 13 Jun 2023 16:23:20 +0800	[thread overview]
Message-ID: <CADm8TekHVfLHzKBLRfj7TwZiw=eL=VSgPpuhdpx_FSjNUXNtHQ@mail.gmail.com> (raw)

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Hello,

Our static analysis tool finds some possible data races in the OCFS2 file
system in Linux 6.4.0-rc6.

In most calling contexts, the variables  such as res->lockname.name and
res->owner are accessed with holding the lock res->spinlock. Here is an
example:

  lockres_seq_start() --> Line 539 in dlmdebug.c
    spin_lock(&res->spinlock); --> Line 574 in dlmdebug.c (Lock
res->spinlock)
    dump_lockres(res, ...); --> Line 575 in fs/ocfs2/dlm/dlmdebug.c
      stringify_lockname(res->lockname.name, ...);  --> Line 493 in
dlmdebug.c (Access res->lockname.name)
      scnprintf(..., res->owner, ...);  -->Line 498 in dlmdebug.c (Access
res->owner)

However, in the following calling contexts:

  dlm_deref_lockres_worker() --> Line 2439 in dlmmaster.c
    dlm_drop_lockres_ref_done() --> Line 2459 in dlmmaster.c
      lockname = res->lockname.name; --> Line 2416 in dlmmaster.c (Access
res->lockname.name)

  dlm_get_lock_resource() --> Line 701 in dlmmaster.c
    if (res->owner != dlm->node_num) --> Line 1023 in dlmmaster.c (Access
res->owner)

The variables res->lockname.name and res->owner are accessed respectively
without holding the lock res->spinlock, and thus data races can occur.

I am not quite sure whether these possible data races are real and how to
fix
them if they are real.

Any feedback would be appreciated, thanks!

Reported-by: BassCheck <bass@buaa.edu.cn> <bass@buaa.edu.cn>

Best wishes,
Tuo Li

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