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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Greg KH <greg@kroah.com>,
	mingo@kernel.org, mgorman@suse.de, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, bristot@redhat.com,
	joshdon@google.com, valentin.schneider@arm.com,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/9] debugfs: Implement debugfs_create_str()
Date: Fri, 26 Mar 2021 15:58:37 +0100	[thread overview]
Message-ID: <c1be3728-40e7-f200-ece0-cd3f11349f65@rasmusvillemoes.dk> (raw)
In-Reply-To: <20210326142230.GJ4746@worktop.programming.kicks-ass.net>

On 26/03/2021 15.22, Peter Zijlstra wrote:
> On Fri, Mar 26, 2021 at 01:53:59PM +0100, Rasmus Villemoes wrote:
>> On 26/03/2021 12.38, Peter Zijlstra wrote:
> 
>>> +
>>> +again:
>>> +	rcu_read_lock();
>>> +	str = rcu_dereference(*(char **)file->private_data);
>>> +	len = strlen(str) + 1;
>>> +
>>> +	if (!copy || copy_len < len) {
>>> +		rcu_read_unlock();
>>> +		kfree(copy);
>>> +		copy = kmalloc(len + 1, GFP_KERNEL);
>>> +		if (!copy) {
>>> +			debugfs_file_put(dentry);
>>> +			return -ENOMEM;
>>> +		}
>>> +		copy_len = len;
>>> +		goto again;
>>> +	}
>>> +
>>> +	strncpy(copy, str, len);
>>> +	copy[len] = '\n';
>>> +	copy[len+1] = '\0';
>>> +	rcu_read_unlock();
>>
>> As noted (accidentally off-list), this is broken. I think you want this
>> on top
>>
>> - len = strlen(str) + 1;
>> + len = strlen(str);
> 
>   kmalloc(len + 2, ...);

No, because nul-terminating the stuff you pass to
simple_read_from_buffer is pointless cargo-culting. Yeah, read_file_bool
does it, but that's just bogus.

>> - strncpy(copy, str, len);
>> + memcpy(copy, str, len);
>>   copy[len] = '\n';
>> - copy[len+1] = '\0';
> 
> I'll go with strscpy() I tihnk, something like:
> 
> 	len = strscpy(copy, str, len);
> 	if (len < 0)
> 		return len;

To what end? The only way that could possibly return -EFOO is if the
nul-terminator in str vanished between the strlen() and here, and in
that case you have bigger problems.

> 	copy[len] = '\n';
> 	copy[len + 1] = '\0';
> 
>>> +EXPORT_SYMBOL_GPL(debugfs_read_file_str);
>>
>> Why?
> 
> Copy-pasta from debugfs_*_bool(). This thing seems to export everything
> and I figured I'd go along with that.

I thought the convention was not to export anything until the kernel
itself had a (modular) user. But I can't find that stated under
Documentation/ anywhere - but it does say "Every function that is
exported to loadable modules using
``EXPORT_SYMBOL`` or ``EXPORT_SYMBOL_GPL`` should have a kernel-doc
comment.". Anyway, the *_bool stuff doesn't seem to be something to be
copy-pasted.

Rasmus

  reply	other threads:[~2021-03-26 14:59 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-26 10:33 [PATCH 0/9] sched: Clean up SCHED_DEBUG Peter Zijlstra
2021-03-26 10:33 ` [PATCH 1/9] sched/numa: Allow runtime enabling/disabling of NUMA balance without SCHED_DEBUG Peter Zijlstra
2021-03-26 10:33 ` [PATCH 2/9] sched: Remove sched_schedstats sysctl out from under SCHED_DEBUG Peter Zijlstra
2021-03-26 10:33 ` [PATCH 3/9] sched: Dont make LATENCYTOP select SCHED_DEBUG Peter Zijlstra
2021-03-26 10:33 ` [PATCH 4/9] sched: Move SCHED_DEBUG to debugfs Peter Zijlstra
2021-03-26 11:06   ` Greg KH
2021-04-07 10:46   ` Valentin Schneider
2021-04-07 12:26     ` Peter Zijlstra
2021-04-07 12:57       ` Valentin Schneider
2021-03-26 10:33 ` [PATCH 5/9] sched,preempt: Move preempt_dynamic to debug.c Peter Zijlstra
2021-03-26 10:33 ` [PATCH 6/9] debugfs: Implement debugfs_create_str() Peter Zijlstra
2021-03-26 11:05   ` Greg KH
2021-03-26 11:18     ` Peter Zijlstra
2021-03-26 11:30       ` Greg KH
2021-03-26 11:38         ` [PATCH v2 " Peter Zijlstra
2021-03-26 12:18           ` Greg KH
2021-03-26 12:53           ` Rasmus Villemoes
2021-03-26 12:57             ` Greg KH
2021-03-26 13:10               ` Rasmus Villemoes
2021-03-26 14:12                 ` Peter Zijlstra
2021-03-26 14:19                   ` Greg KH
2021-03-26 14:22             ` Peter Zijlstra
2021-03-26 14:58               ` Rasmus Villemoes [this message]
2021-03-26 15:19                 ` Peter Zijlstra
2021-03-27 10:41                   ` Greg KH
2021-03-26 14:50   ` [PATCH v3 " Peter Zijlstra
2021-03-27 10:42     ` Greg KH
2021-03-27 22:24   ` [PATCH " Al Viro
2021-03-28  0:33     ` Steven Rostedt
2021-03-26 10:33 ` [PATCH 7/9] sched,debug: Convert sysctl sched_domains to debugfs Peter Zijlstra
2021-03-26 13:11   ` Dietmar Eggemann
2021-04-07 10:46   ` Valentin Schneider
2021-04-07 12:18     ` Peter Zijlstra
2021-03-26 10:34 ` [PATCH 8/9] sched: Move /proc/sched_debug " Peter Zijlstra
2021-03-26 11:05   ` Greg KH
2021-03-26 10:34 ` [PATCH 9/9] sched,fair: Alternative sched_slice() Peter Zijlstra
2021-03-26 12:08   ` Dietmar Eggemann
2021-03-26 14:07     ` Peter Zijlstra
2021-03-26 15:37   ` Vincent Guittot
2021-03-26 18:30     ` Peter Zijlstra
2021-04-12 10:14 [PATCH v2 0/9] sched: Clean up SCHED_DEBUG Peter Zijlstra
2021-04-12 10:14 ` [PATCH v2 6/9] debugfs: Implement debugfs_create_str() Peter Zijlstra

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