Re: creating backups in temporary directories

[Stefan Monnier]

>     But in a directory with mode 1777 when you open a file that *you* own,
>     nobody else can remove it or rename it, so normally nobody can replace it
>     with a symlink.  Emacs creates the problem when it moves /tmp/foo to
>     /tmp/foo~ at which point /tmp/foo is free for an attacker to take.

> This suggests that Emacs should always do backup by copying
> in such directories.  Would that solve the problem?

It replaces one problem by another.  More specifically, it's safe to do
a backup using copying on one condition: that there was already a backup
(owned by you).  Otherwise, we bump into the problem I mentioned originally:
some other user could see you're editing /tmp/foo and create a /tmp/foo~
symlink before you create it.


        Stefan