Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) client-ip=2620:137:e000::3:5;
Message-ID: <1793b780-cd15-b6a3-f951-c19a14a1310c@linux.intel.com>
Date:   Tue, 10 Oct 2023 11:51:32 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101
 Thunderbird/102.15.1
Subject: Re: [PATCH] selftests/x86/lam: Zero out buffer for readlink()
To:     kirill.shutemov@linux.intel.com
Cc:     dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org,
        shuah@kernel.org, linux-kselftest@vger.kernel.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, weihong.zhang@intel.com
References: <20230923233346.12726-1-binbin.wu@linux.intel.com>
 <20230927110219.b5n3fbbwrxtcwtzp@box.shutemov.name>
From:   Binbin Wu <binbin.wu@linux.intel.com>
In-Reply-To: <20230927110219.b5n3fbbwrxtcwtzp@box.shutemov.name>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk


On 9/27/2023 7:02 PM, kirill.shutemov@linux.intel.com wrote:
> On Sun, Sep 24, 2023 at 07:33:46AM +0800, Binbin Wu wrote:
>> Zero out the buffer for readlink() since readlink() does not append a
>> terminating null byte to the buffer.
>>
>> Fixes: 833c12ce0f430 ("selftests/x86/lam: Add inherit test cases for linear-address masking")
>>
>> Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
>> ---
>>   tools/testing/selftests/x86/lam.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/x86/lam.c b/tools/testing/selftests/x86/lam.c
>> index eb0e46905bf9..9f06942a8e25 100644
>> --- a/tools/testing/selftests/x86/lam.c
>> +++ b/tools/testing/selftests/x86/lam.c
>> @@ -680,7 +680,7 @@ static int handle_execve(struct testcases *test)
>>   		perror("Fork failed.");
>>   		ret = 1;
>>   	} else if (pid == 0) {
>> -		char path[PATH_MAX];
>> +		char path[PATH_MAX] = {0};
> Shouldn't it be PATH_MAX+1 to handle the case when readlink(2) stores
> exactly PATH_MAX bytes into the buffer?
According to the definition of PATH_MAX in include/uapi/linux/limits.h
#define PATH_MAX        4096    /* # chars in a path name including nul */

IIUC, Linux limits the path length to 4095 and PATH_MAX includes the 
terminating nul.


>
>>   
>>   		/* Set LAM mode in parent process */
>>   		if (set_lam(lam) != 0)
>>
>> base-commit: ce9ecca0238b140b88f43859b211c9fdfd8e5b70
>> -- 
>> 2.25.1
>>