Re: [PATCH] kernel/rcutorture.c: use scnprintf() instead of sprintf()

[Chen Gang <gang.chen@asianux.com>]

On 10/15/2013 08:54 AM, Chen Gang wrote:
> On 10/14/2013 07:28 PM, Paul E. McKenney wrote:
>> On Mon, Oct 14, 2013 at 04:38:55PM +0800, Chen Gang wrote:
>>> If the contents is more than 4096 bytes (e.g. if have 1K cpus), current
>>> sprintf() will cause memory overflow.
>>>
>>> They are all test information which can be truncated, so use scnprintf()
>>> instead of sprintf(), also add 'max' parameter for related functions,
>>> also notice 80 columns boundary and parameters alignments.
>>>
>>> Test case:
>>>
>>>   Fedora16 x86_64, 2 CPUs, 2GB RAM, [in/rm]mod with "torture_type=srcu".
>>>
>>>     let maximize buffer to 256 to truncate in rcu_torture_printk().
>>>     let maximize buffer to 410 to may truncate in srcu_torture_stats().
>>>     let maximize buffer to 4096 (original size) to print full.
>>>
>>>   it is a rcu test module, so not need additional test or consideration.
>>>
>>> Signed-off-by: Chen Gang <gang.chen@asianux.com>
>>
>> At first glance, not a bad start.
>>
>> Suppose that your goal was to make it avoid truncation.  What would you
>> do differently?
>>
> 
> One simple way: using snprintf() instead of scnprintf() in the related
> printing functions. Then call them with "buffer == NULL" to get buffer
> size, next allocate it and call it again ...
> 

Oh, this simple way assumes the printing contents will not be changed
during the 2 calls.

> Hmm... it is only a test module, is it worth enough to try to make it
> avoid truncation? If some members (quite few members) find truncation,
> they can simply extend maximize buffer to avoid it when testing.
> 
> But if we do not fix this bug, when memory overflow, the OS may not stop
> immediately, then it will/may lead the testers to face various amazing
> things (which is not quite easy to find root cause).
> 
> 
> All together, making contribution with efficiency and without negative
> effect is our goal, so ...
> 
> 
> Thanks.
> 
>> 							Thanx, Paul
>>
>>> ---
>>>  kernel/rcutorture.c |  110 +++++++++++++++++++++++++++-----------------------
>>>  1 files changed, 59 insertions(+), 51 deletions(-)
>>>
>>> diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
>>> index be63101..107fd76 100644
>>> --- a/kernel/rcutorture.c
>>> +++ b/kernel/rcutorture.c
>>> @@ -370,7 +370,7 @@ struct rcu_torture_ops {
>>>  	void (*call)(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
>>>  	void (*cb_barrier)(void);
>>>  	void (*fqs)(void);
>>> -	int (*stats)(char *page);
>>> +	int (*stats)(char *page, int max);
>>>  	int irq_capable;
>>>  	int can_boost;
>>>  	const char *name;
>>> @@ -572,20 +572,20 @@ static void srcu_torture_barrier(void)
>>>  	srcu_barrier(&srcu_ctl);
>>>  }
>>>
>>> -static int srcu_torture_stats(char *page)
>>> +static int srcu_torture_stats(char *page, int max)
>>>  {
>>>  	int cnt = 0;
>>>  	int cpu;
>>>  	int idx = srcu_ctl.completed & 0x1;
>>>
>>> -	cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
>>> -		       torture_type, TORTURE_FLAG, idx);
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "%s%s per-CPU(idx=%d):",
>>> +			torture_type, TORTURE_FLAG, idx);
>>>  	for_each_possible_cpu(cpu) {
>>> -		cnt += sprintf(&page[cnt], " %d(%lu,%lu)", cpu,
>>> -			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
>>> -			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
>>> +		cnt += scnprintf(&page[cnt], max - cnt, " %d(%lu,%lu)", cpu,
>>> +				per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
>>> +				per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
>>>  	}
>>> -	cnt += sprintf(&page[cnt], "\n");
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n");
>>>  	return cnt;
>>>  }
>>>
>>> @@ -1047,7 +1047,7 @@ rcu_torture_reader(void *arg)
>>>   * Create an RCU-torture statistics message in the specified buffer.
>>>   */
>>>  static int
>>> -rcu_torture_printk(char *page)
>>> +rcu_torture_printk(char *page, int max)
>>>  {
>>>  	int cnt = 0;
>>>  	int cpu;
>>> @@ -1065,61 +1065,69 @@ rcu_torture_printk(char *page)
>>>  		if (pipesummary[i] != 0)
>>>  			break;
>>>  	}
>>> -	cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG);
>>> -	cnt += sprintf(&page[cnt],
>>> -		       "rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
>>> -		       rcu_torture_current,
>>> -		       rcu_torture_current_version,
>>> -		       list_empty(&rcu_torture_freelist),
>>> -		       atomic_read(&n_rcu_torture_alloc),
>>> -		       atomic_read(&n_rcu_torture_alloc_fail),
>>> -		       atomic_read(&n_rcu_torture_free));
>>> -	cnt += sprintf(&page[cnt], "rtmbe: %d rtbke: %ld rtbre: %ld ",
>>> -		       atomic_read(&n_rcu_torture_mberror),
>>> -		       n_rcu_torture_boost_ktrerror,
>>> -		       n_rcu_torture_boost_rterror);
>>> -	cnt += sprintf(&page[cnt], "rtbf: %ld rtb: %ld nt: %ld ",
>>> -		       n_rcu_torture_boost_failure,
>>> -		       n_rcu_torture_boosts,
>>> -		       n_rcu_torture_timers);
>>> -	cnt += sprintf(&page[cnt],
>>> -		       "onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
>>> -		       n_online_successes, n_online_attempts,
>>> -		       n_offline_successes, n_offline_attempts,
>>> -		       min_online, max_online,
>>> -		       min_offline, max_offline,
>>> -		       sum_online, sum_offline, HZ);
>>> -	cnt += sprintf(&page[cnt], "barrier: %ld/%ld:%ld",
>>> -		       n_barrier_successes,
>>> -		       n_barrier_attempts,
>>> -		       n_rcu_torture_barrier_error);
>>> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "%s%s ",
>>> +			torture_type, TORTURE_FLAG);
>>> +	cnt += scnprintf(&page[cnt], max - cnt,
>>> +			"rtc: %p ver: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
>>> +			rcu_torture_current,
>>> +			rcu_torture_current_version,
>>> +			list_empty(&rcu_torture_freelist),
>>> +			atomic_read(&n_rcu_torture_alloc),
>>> +			atomic_read(&n_rcu_torture_alloc_fail),
>>> +			atomic_read(&n_rcu_torture_free));
>>> +	cnt += scnprintf(&page[cnt], max - cnt,
>>> +			"rtmbe: %d rtbke: %ld rtbre: %ld ",
>>> +			atomic_read(&n_rcu_torture_mberror),
>>> +			n_rcu_torture_boost_ktrerror,
>>> +			n_rcu_torture_boost_rterror);
>>> +	cnt += scnprintf(&page[cnt], max - cnt,
>>> +			"rtbf: %ld rtb: %ld nt: %ld ",
>>> +			n_rcu_torture_boost_failure,
>>> +			n_rcu_torture_boosts,
>>> +			n_rcu_torture_timers);
>>> +	cnt += scnprintf(&page[cnt], max - cnt,
>>> +			"onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
>>> +			n_online_successes, n_online_attempts,
>>> +			n_offline_successes, n_offline_attempts,
>>> +			min_online, max_online,
>>> +			min_offline, max_offline,
>>> +			sum_online, sum_offline, HZ);
>>> +	cnt += scnprintf(&page[cnt], max - cnt,
>>> +			"barrier: %ld/%ld:%ld",
>>> +			n_barrier_successes,
>>> +			n_barrier_attempts,
>>> +			n_rcu_torture_barrier_error);
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n%s%s ",
>>> +			torture_type, TORTURE_FLAG);
>>>  	if (atomic_read(&n_rcu_torture_mberror) != 0 ||
>>>  	    n_rcu_torture_barrier_error != 0 ||
>>>  	    n_rcu_torture_boost_ktrerror != 0 ||
>>>  	    n_rcu_torture_boost_rterror != 0 ||
>>>  	    n_rcu_torture_boost_failure != 0 ||
>>>  	    i > 1) {
>>> -		cnt += sprintf(&page[cnt], "!!! ");
>>> +		cnt += scnprintf(&page[cnt], max - cnt, "!!! ");
>>>  		atomic_inc(&n_rcu_torture_error);
>>>  		WARN_ON_ONCE(1);
>>>  	}
>>> -	cnt += sprintf(&page[cnt], "Reader Pipe: ");
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "Reader Pipe: ");
>>>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
>>> -		cnt += sprintf(&page[cnt], " %ld", pipesummary[i]);
>>> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
>>> -	cnt += sprintf(&page[cnt], "Reader Batch: ");
>>> +		cnt += scnprintf(&page[cnt], max - cnt, " %ld", pipesummary[i]);
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n%s%s ",
>>> +			torture_type, TORTURE_FLAG);
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "Reader Batch: ");
>>>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
>>> -		cnt += sprintf(&page[cnt], " %ld", batchsummary[i]);
>>> -	cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
>>> -	cnt += sprintf(&page[cnt], "Free-Block Circulation: ");
>>> +		cnt += scnprintf(&page[cnt], max - cnt, " %ld",
>>> +				batchsummary[i]);
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n%s%s ",
>>> +			torture_type, TORTURE_FLAG);
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "Free-Block Circulation: ");
>>>  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
>>> -		cnt += sprintf(&page[cnt], " %d",
>>> -			       atomic_read(&rcu_torture_wcount[i]));
>>> +		cnt += scnprintf(&page[cnt], max - cnt, " %d",
>>> +				atomic_read(&rcu_torture_wcount[i]));
>>>  	}
>>> -	cnt += sprintf(&page[cnt], "\n");
>>> +	cnt += scnprintf(&page[cnt], max - cnt, "\n");
>>>  	if (cur_ops->stats)
>>> -		cnt += cur_ops->stats(&page[cnt]);
>>> +		cnt += cur_ops->stats(&page[cnt], max - cnt);
>>>  	return cnt;
>>>  }
>>>
>>> @@ -1136,7 +1144,7 @@ rcu_torture_stats_print(void)
>>>  {
>>>  	int cnt;
>>>
>>> -	cnt = rcu_torture_printk(printk_buf);
>>> +	cnt = rcu_torture_printk(printk_buf, sizeof(printk_buf));
>>>  	pr_alert("%s", printk_buf);
>>>  }
>>>
>>> -- 
>>> 1.7.7.6
>>>
>>
>>
>>
> 
> 


-- 
Chen Gang