linux-kernel - Re: [PATCH v2] locktorture: Fix NULL pointer when torture

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Date:	Sun, 6 Mar 2016 21:40:07 -0800
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	peterz@...radead.org, mingo@...hat.com,
	Josh Triplett <josh@...htriplett.org>,
	"Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>
Subject: Re: [PATCH v2] locktorture: Fix NULL pointer when torture_type is
 invalid

On Mon, 07 Mar 2016, Kefeng Wang wrote:
>On 2016/3/3 16:36, Davidlohr Bueso wrote:

>> +    /*
>> +     * Indicates early cleanup, meaning that the test has not run,
>> +     * such as when passing bogus args when loading the module. As
>> +     * such, only perform the underlying torture-specific cleanups,
>> +     * and avoid anything related to locktorture.
>> +     */
>> +    if (!cxt.lwsa)
>> +        goto end;
>
>Sorry for the late response, the cxt.lrsa should be taken into account too.

I am taking it into account, note that we kfree lwsa if lrsa fails memory
allocation. Of course we should be defensive, so go ahead and explicitly set
it to nil. v2 below, otherwise same patch.

-----8<--------------------------
Subject: [PATCH v2] locktorture: Fix nil pointer dereferencing for cleanup paths

It has been found that paths that invoke cleanups through
lock_torture_cleanup() can incur in nil pointer dereferencing
bugs during the statistics printing phase. This is mainly
because we should not be calling into statistics before we are
sure things have been setup correctly.

Specifically, early checks (and the need for handling this in
the cleanup call) only include parameter checks and basic
statistics allocation. Once we start write/read kthreads
we then consider the test as started. As such, update the func
in question to check for cxt.lwsa writer stats, if not set,
we either have a bogus parameter or ENOMEM situation and
therefore only need to deal with general torture calls

Reported-by: Kefeng Wang <wangkefeng.wang@...wei.com>
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
  kernel/locking/locktorture.c | 12 ++++++++++++
  1 file changed, 12 insertions(+)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 8ef1919..b5bc243 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -748,6 +748,15 @@ static void lock_torture_cleanup(void)
  	if (torture_cleanup_begin())
  		return;
  
+	/*
+	 * Indicates early cleanup, meaning that the test has not run,
+	 * such as when passing bogus args when loading the module. As
+	 * such, only perform the underlying torture-specific cleanups,
+	 * and avoid anything related to locktorture.
+	 */
+	if (!cxt.lwsa)
+		goto end;
+
  	if (writer_tasks) {
  		for (i = 0; i < cxt.nrealwriters_stress; i++)
  			torture_stop_kthread(lock_torture_writer,
@@ -776,6 +785,7 @@ static void lock_torture_cleanup(void)
  	else
  		lock_torture_print_module_parms(cxt.cur_ops,
  						"End of test: SUCCESS");
+end:
  	torture_cleanup_end();
  }
  
@@ -870,6 +880,7 @@ static int __init lock_torture_init(void)
  			VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
  			firsterr = -ENOMEM;
  			kfree(cxt.lwsa);
+			cxt.lwsa = NULL;
  			goto unwind;
  		}
  
@@ -878,6 +889,7 @@ static int __init lock_torture_init(void)
  			cxt.lrsa[i].n_lock_acquired = 0;
  		}
  	}
+
  	lock_torture_print_module_parms(cxt.cur_ops, "Start of test");
  
  	/* Prepare torture context. */
-- 
2.1.4