How cheating is PHP file_exists_PHP Tutorial

I found a problem and share it with you today. Let me describe the whole process.

Problem

The company has a framework written based on smarty. I am responsible for the upgrade of PHP. After the maintenance staff deployed the new environment, the testers came to me and asked me frequently An error is reported (error: file cannot be found). I traced the code and it turned out to be an error reported by smarty.

Error: The file reported here does not exist.

Thought process:

1. I thought it was because there was no such file in the program, but it turned out that the file was. What happened?

2. Later, I guessed whether there was a problem with the PHP kernel. I looked through the relevant PHP kernel files and found no problem. As a result, I told the project manager about the entire process. ——The matter has not been resolved, so let’s just let it go. The upgrade is delayed for now.

I discovered this problem again today. My first reaction was whether the PHP version had been upgraded. I found out that it had not. ——Later, I set the entire directory to 777 and everything was fine (chmod 777 -R directory). I wonder if it is a problem with the file_exists() method.

So, I conducted relevant debugging and experiments.

Debugging process

Debugging code:

Directory:

Observe each permission: test does not have any permissions for www, while the execution file index.php has read and write execution permissions, and the included file test.txt has read and write permissions.

Run result:

The execution permission of the directory affects file_exists()

1. Give test the maximum permission - 755

Since it is successful, it means that the file_exists() function is restricted by directory permissions.

So what kind of directory permissions affect file_exists()?

I did a few experiments:

1. In any superior directory of the file, if it only has write permission, the file does not exist;

2. File Any parent directory with only read permission will report that the file does not exist;

3. When all parent directories have execution permission, the file will be reported to exist and everything is normal.

The result shows that file_exists() recursively determines whether each directory has execution permission when determining whether a file exists.

Change the file path to a relative path and get the same result.

Summary

It is not mentioned in the PHP manual that file_exists will be affected by the execution permission of the directory. This article is used to inform developers who also have this problem. Just take this as a warning.

Additional information

Thank you everyone for your comments, they are very useful. After everyone's opinions, I checked the manual again. Indeed, if the directory does not have execution permissions, the php-fpm application process cannot search for files in this directory. Of course, it will be considered that the file does not exist (actually it is considered that there is no executable directory). does not exist).

You can consider the contents of the manual together, mainly about execution permissions. I won’t go into details about read and write permissions here (generally they are easy to understand).

Obviously in the manual, there are clear instructions on the execution permission of the directory. Execute permission on the directory means having the right to be searched.

Recommendation

If this article is helpful to you or helps you solve this kind of problem, please recommend it. Let me have stronger motivation for writing.