`cp` behaves differently on read-only directories

[suimong]

Observe the output of the following:

mkdir -p a/b/c/d
touch a/b/c/d/bar.txt

chmod -R -w a

cp -r a b
uutils-cp -r a c

tree -p a b c

All directories under a and including itself (i.e. a, b, c, d) now has permission 555. (coreutils) cp -r respects readonly flags on directories, thus each subdirectory in this tree b/b/c/d also has permission 555, the same as source a, but each subdirectory in the uutils-cped tree c/b/c/d now has permission 755.

Another observable deviation is that, cp -a a b works as expected, but uutils-cp -a a b will raise permission denied error.

[jacobgc]

As far as I can tell, cp (coreutils) seems to preserve the permission mode for files and folders by default, adding --no-preserve=mode produces the same as uuitls-cp for directories, but not for files...

You also get a permission denied error using -p. As far as I can tell it will make the subdirectory, remove the write flag, and then try and copy in bar.txt

[suimong]

@jacobgc Yes, that's my observation as well.

[ShaiKKO]

The existing code does not recognize the permissions model, looks like currently it applies a uniform umask reset on the permissions of both files, and directories which is not how GNU permission model handles this.

There is a distinction in how permissions are handled that is currently missing, the core issue is that it is treating directories and files identically when they follow different preservation rules.

The permission model should recognize three states:

• Default recursive copy: Directories maintain their original permissions & files receive umask-filtered permissions.
• Explicit --no-preserve=mode - apply umask to everything
• Explicit preservation flags - This is already being handled correctly

The fix would require intercepting the permission logic at the point where blanket umask handling then

• Detect when we're dealing with a directory vs file
• Differentiate between no preservation flag provided and if a user explicitly specified --no-preserve
• Ensure directories bypass the standard umask unless given the flag.