[Rd] unlink() on "~" removes the home directory

Tomas Kalibera tom@@@k@||ber@ @end|ng |rom gm@||@com
Mon Mar 23 18:03:58 CET 2020

To clarify, these issues are about deleting the contents of the home 
directory, not the directory itself, which cannot be deleted by ordinary 
users on today's systems. Unfortunately this has to be fixed in the code 
that calls unlink(), such code must be aware of the expansions. The "R 
CMD build" case as you write has been fixed, if anyone finds any other 
instance of this problem in base R, please report, it will be fixed as 
well. The new argument "expand" has been added to unlink() to make these 
fixes easier.

A variation on what you propose: tilde ("~") is now treated the same way 
as "." and ".." have already been by unlink(), which means it will never 
be considered for deletion (not even with expand=TRUE). There are still 
a number of ways to delete the contents of one's home directory, 
including tilde expansion with user name, with directory separators, 
etc.  This special treatment of "~" will prevent only one pattern of the 
problem. One should always be careful when recursively/programmatically 
deleting files.

Also, the new behavior can cause trouble in some cases when a file or 
directory named tilde exists, but hopefully not as bad as deleting the 
contents of user home directory. In principle, such file can still be 
deleted from R using a combination of tilde and wildcards with wildcard 
expansion enabled.


On 2/26/20 11:47 PM, Gábor Csárdi wrote:
> Well, unlink() does what it is supposed to do, so you could argue that
> there is nothing wrong with it. Also, nobody would call unlink() on
> "~", right?
> The situation is not so simple, however. E.g. if you happen to have a
> directory called "~", and you iterate over all files and directories
> to selectively remove some of them, then your code might end up
> calling unlink on the local "~" directory, and then your home is gone.
> But you would not create a directory named "~", that is just asking
> for trouble. Well, surely, _intentionally_ you would not do that.
> Unintentionally, you might. E.g. something like this is enough:
> # Create a subpath within a base directory
> badfun <- function(base = ".", path) {
>    dir.create(file.path(base, path), recursive = TRUE, showWarnings = FALSE)
> }
> badfun(path = "~/foo")
> (If you did run this, be very careful how you remove the directory called "~"!)
> A real example is `R CMD build` which deletes the home directory of
> the current user if the root of the package contains a non-empty "~"
> directory. Luckily this is now fixed in R-devel, so R 4.0.0 will do
> better. (R 3.6.3 will not.) See
> https://github.com/wch/r-source/commit/1d4f7aa1dac427ea2213d1f7cd7b5c16e896af22
> I have seen several bug reports about various packages (that call R
> CMD build) removing the home directory, so this indeed happens in
> practice to a number of people. The commit above will fix `R CMD
> build`, but it would be great to "fix" this in general.
> It seems pretty hard to prevent users from creating of a "~"
> directory. But preventing unlink() from deleting "~" does not actually
> seem too hard. If unlink() could just refuse removing "~" (when expand
> = TRUE), that would be great. It seems to me that the current behavior
> is very-very rarely intended, and its consequences are potentially
> disastrous.
> If unlink("~", recursive = TRUE) errors, you can still remove a local
> "~" file/dir with unlink("./~", ...). And you can still remove your
> home directory if you really want to do that, with
> unlink(path.expand("~"), ...). So no functionality is lost.
> Also, if anyone is aware of packages/functions that tend to create "~"
> directories or files, please let me know.
> I would be happy to submit a patch for the new unlink("~") behavior.
> Thanks,
> Gabor
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