Files without write permission can be deleted

[bbaldino]

Given the following code:

val fs = MemoryFileSystemBuilder.newLinux().build()
val readOnlyFile = fs.getPath("file1.txt")
Files.createFile(readOnlyFile)
val perms = PosixFilePermissions.fromString("r--r--r--")
Files.setPosixFilePermissions(readOnlyFile, perms)
println("writable? ${Files.isWritable(readOnlyFile)}")
Files.delete(readOnlyFile)
println("exists? ${Files.exists(readOnlyFile)}")

It will print:

writable? false
exists? false

So even though the file only has read permissions, it can still be deleted.

[bbaldino]

It looks like maybe it's just a missing call to checkAccess around here? I'll take a shot at a PR with a change there and see how it goes.

[marschall]

It is my understanding that only a write permission on the parent directory is needed to delete a file. (And probably also the execute permission on all parents).

The following works for me

touch to-delete
chmod a-w to-delete
rm to-delete

https://en.wikipedia.org/wiki/Rm_(Unix)

Usually, on most filesystems, deleting a file requires write permission on the parent directory

[bbaldino]

When I try that, I get a prompt:

-r--r--r-- 1 bbaldino bbaldino      0 May 25 05:30 to-delete
bbaldino:/tmp$ rm to-delete
rm: remove write-protected regular empty file 'to-delete'? y

And it does delete it. Trying it from a different user gives the same prompt but fails even if they enter 'y'. So I guess it depends on the user doing the delete?

bbaldino:/tmp$ touch to-delete
bbaldino:/tmp$ chmod a-w to-delete
bbaldino:/tmp$ sudo su other_user
other_user:/tmp$ rm to-delete
rm: remove write-protected regular empty file 'to-delete'? y
rm: cannot remove 'to-delete': Operation not permitted

Even though the containing directory (tmp) is

drwxrwxrwt 239 root root 20480 May 25 05:35 tmp

EDIT: Interesting! The bit right after what you pasted explains it I guess:

(Note that, confusingly for beginners, permissions on the file itself are irrelevant. However, GNU rm asks for confirmation if a write-protected file is to be deleted, unless the -f option is used.)

Good to know, that does seem counterintuitive but I guess no bug here. Though wonder why it doesn't work for the other user.

Thanks for the great library, saved me when testing some complicated filesystem interactions.

[marschall]

Yeah, UNIX permission can be confusing at first.

Though wonder why it doesn't work for the other user.

Does the other have execute permission on all parent folders?

You're welcome.

[bbaldino]

Though wonder why it doesn't work for the other user.

Does the other have execute permission on all parent folders?

Yeah this was in /tmp/ so tmp was the only parent.

[marschall]

Yeah this was in /tmp/ so tmp was the only parent.

Strictly speaking / as well but the other user will have execute permission there as well.