| In the order I happen to think of them: Filenames may be straightforward on the filesystem level, but a lot of UNIX programs do weird things with them. Many programs use "-" to mean STDIN or STDOUT as appropriate where it is used. Bash has a somewhat ill-conceived feature where it synthesizes a /dev/tcp/$host/$port filesystem that will write to TCP or UDP sockets. Most people don't know about this, a few people think it's a UNIX feature rather than a bash-ism. The fact that multiple /s will be normalized to be the same as one sometimes trips up security code or code trying to validate that some particular file isn't used (i.e., checking that the filename doesn't start with /dev or a list of other blacklisted directories will fail if the user passes //dev). Symlinks! Oh, gosh, symlinks. Were this not a stream-of-consciousness dump they probably should come first. You can do terrible things with symlinks, like upload a tarball or zip file that creates a symlink to an arbitrary location in the system, then use that symlink reference as a directory reference to plop a file down. (Some archivers prevent this, others don't.) Also, /dev is just a convention, it's possible to place device nodes anywhere you want. You can also pretty much mount arbitrary things in arbitrary places via bind mounts. Hard links can also cause some fun with code that assumes file systems aren't cyclic. Windows technically has a lot of these features but they're harder to get to and less well known whereas UNIX uses the various links in base Linux installs and they're readily available. |