linux-kernel - Re: [PATCH V2] perf cpumap: Fix snprintf overflow check

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Date:   Tue, 24 Mar 2020 15:44:15 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     peterz@...radead.org, mingo@...hat.com, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, kan.liang@...ux.intel.com,
        zhe.he@...driver.com, dzickus@...hat.com, jstancek@...hat.com,
        David Laight <David.Laight@...lab.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH V2] perf cpumap: Fix snprintf overflow check

Le 24/03/2020 à 13:50, Arnaldo Carvalho de Melo a écrit :
> Em Tue, Mar 24, 2020 at 08:03:19AM +0100, Christophe JAILLET escreveu:
>> 'snprintf' returns the number of characters which would be generated for
>> the given input.
>>
>> If the returned value is *greater than* or equal to the buffer size, it
>> means that the output has been truncated.
>>
>> Fix the overflow test accordingling.
>                                    y
>
> You forgot to CC David and add this to your patch, which I did:
>
> Suggested-by: David Laight <David.Laight@...LAB.COM>
>
> Ok?

No problem for me.

The to: and cc: list are (at least should be :)) the ones given by 
get_maintainer, and I was not aware of the 'Suggested-by' tag.

BTW, thanks for fixing the typo in the description.

CJ


> - Arnaldo
>   
>> Fixes: 7780c25bae59f ("perf tools: Allow ability to map cpus to nodes easily")
>> Fixes: 92a7e1278005b ("perf cpumap: Add cpu__max_present_cpu()")
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
>> ---
>> V2: keep snprintf
>>      modifiy the tests for truncated output
>>      Update subject and description
>> ---
>>   tools/perf/util/cpumap.c | 10 +++++-----
>>   1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/tools/perf/util/cpumap.c b/tools/perf/util/cpumap.c
>> index 983b7388f22b..dc5c5e6fc502 100644
>> --- a/tools/perf/util/cpumap.c
>> +++ b/tools/perf/util/cpumap.c
>> @@ -317,7 +317,7 @@ static void set_max_cpu_num(void)
>>   
>>   	/* get the highest possible cpu number for a sparse allocation */
>>   	ret = snprintf(path, PATH_MAX, "%s/devices/system/cpu/possible", mnt);
>> -	if (ret == PATH_MAX) {
>> +	if (ret >= PATH_MAX) {
>>   		pr_err("sysfs path crossed PATH_MAX(%d) size\n", PATH_MAX);
>>   		goto out;
>>   	}
>> @@ -328,7 +328,7 @@ static void set_max_cpu_num(void)
>>   
>>   	/* get the highest present cpu number for a sparse allocation */
>>   	ret = snprintf(path, PATH_MAX, "%s/devices/system/cpu/present", mnt);
>> -	if (ret == PATH_MAX) {
>> +	if (ret >= PATH_MAX) {
>>   		pr_err("sysfs path crossed PATH_MAX(%d) size\n", PATH_MAX);
>>   		goto out;
>>   	}
>> @@ -356,7 +356,7 @@ static void set_max_node_num(void)
>>   
>>   	/* get the highest possible cpu number for a sparse allocation */
>>   	ret = snprintf(path, PATH_MAX, "%s/devices/system/node/possible", mnt);
>> -	if (ret == PATH_MAX) {
>> +	if (ret >= PATH_MAX) {
>>   		pr_err("sysfs path crossed PATH_MAX(%d) size\n", PATH_MAX);
>>   		goto out;
>>   	}
>> @@ -441,7 +441,7 @@ int cpu__setup_cpunode_map(void)
>>   		return 0;
>>   
>>   	n = snprintf(path, PATH_MAX, "%s/devices/system/node", mnt);
>> -	if (n == PATH_MAX) {
>> +	if (n >= PATH_MAX) {
>>   		pr_err("sysfs path crossed PATH_MAX(%d) size\n", PATH_MAX);
>>   		return -1;
>>   	}
>> @@ -456,7 +456,7 @@ int cpu__setup_cpunode_map(void)
>>   			continue;
>>   
>>   		n = snprintf(buf, PATH_MAX, "%s/%s", path, dent1->d_name);
>> -		if (n == PATH_MAX) {
>> +		if (n >= PATH_MAX) {
>>   			pr_err("sysfs path crossed PATH_MAX(%d) size\n", PATH_MAX);
>>   			continue;
>>   		}
>> -- 
>> 2.20.1
>>