Description:
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On all current PHP versions, move_uploaded_file() creates a 
destination file that is either mode 0600 or 0644 (on Linux, 
anyway), depending on whether move_uploaded_file() needed to copy 
the file across filesystems.

If the file can be moved (renamed), then the resulting file is mode 
0600, because the file was originally created with mkstemp. If the 
file needs to be copied, the resulting mode is 0644 instead 
(assuming a "normal" umask of 022).

This behavior appears (to the script author who isn't familiar with 
how move_uploaded_file works internally) inconsistent and 
surprising, and is undocumented.

Expected result:
----------------
Permissions given to uploaded files should be consistent, depending 
only on the umask setting. In other words, if I pass 
move_uploaded_file() the same parameters with the same umask value, 
I would expect to see the same resulting permissions, regardless of 
whether PHP's temporary file location happens to be on the same file 
system as the final destination.

One could argue that a script author should be aware of this 
behavior, and should therefore find out whether the temporary 
location is on the same file system and plan for the resulting 
behavior. However, that doesn't seem practical. First of all, the 
current behavior isn't documented, so few people are aware of it. 
Secondly, the file system that is used for temporary files may be 
out of the script author's control, and may change without his or 
her knowledge (especially in a shared hosting environment, etc.)

This could have security implications: Uploaded files that used to 
be given mode 0600 and were therefore considered "secure" because 
the script author thought that's "just how PHP works" will suddenly 
start getting mode 0644 if the server admin moves /tmp to a 
dedicated partition, for example. Making the behavior consistent 
(one way or the other) would avoid confusion.

If the behavior can't be made consistent, it would be good to 
document the current behavior so that authors know that relying on 
the mode is not safe.

Actual result:
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Permissions are set to either 0600 or 0644 depending on 
filesystem configuration.