Description:
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This is NOT a security bug! It's only a very misleading error message.

Example:

open_basedir is set to /var/vmail/ (among other directories)
/var/vmail is drwxrwx---  9 vmail    vmail    4096 Sep  2 15:13 .
user.group for fpm pool is www-data.www-data
So, user/group www-data does not have access to it.

Trying to mkdir or write (file_put_contents) within that directory fails with message about open_basedir restriction (see below). However, this message is not correct. It fails because of insufficient permissions. It does NOT fail because of the open_basedir restriction!

If I change permissions to
/var/vmail is drwxrwx--x  9 vmail    vmail    4096 Sep  2 15:13 .
the misleading error message goes away and the file operation succeeds (if permissions in the target area below are correct).

Related to https://bugs.php.net/bug.php?id=69240, I suppose.

Expected result:
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There should be an error message about missing permissions. There should be NO warning about open_basedir at all in this case, as it's wrong: the file is clearly within the allowed paths.
It would fail to enter that directory without open_basedir set as well!
It probably fails to find the dir because it's inaccessible to the pool. I think in this case it should emit a warning "directory does not exist" or something to that effect. But saying that x is not x in an error message is confusing.


Actual result:
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I get a warning on all kinds of file operations (tried is_dir, mkdir, file_put_contents) that includes this text:

PHP Warning:  is_dir(): open_basedir restriction in effect. File(/var/vmail/sieve/whatever/whatever/whatever) is not within the allowed path(s): (...:/var/vmail/sieve/:...) in ....

file_put_contents adds a second message "failed to open stream: Operation not permitted" which might be fine, but the first warning is still wrong. The ...dir operations get only the open_basedir warning.