On Mon, May 24, 2010 at 6:30 AM, Andrew Reid <rei...@bellatlantic.net> wrote: > On Sunday 23 May 2010 18:46:29 Tom Furie wrote: >> On Sun, May 23, 2010 at 10:38:48AM -0400, Andrew Reid wrote: >> > Setting the *directory* noexec seems very bad, since the exec bit >> > on directories controls the ability to cd to it, and turning that >> > off would make it largely useless. >> >> Just for the sake of argument *why* is setting /tmp rw- a bad thing? >> Surely if you put a file there, you know the full pathname, why would >> you need to list or search /tmp? > > Well, I don't actually know for sure that it's bad, but it seems > to invite broken-ness. > > Recursive Makefiles are notorious for cd-ing all over the place, > but then again, that's usually in the source tree, which may or > may not be in /tmp, depending where you unpacked it. > > As a theoretical example, I can easily imagine an installer that > might unpack a set of example configurations into /tmp, and then do > an "ls" to grep out the one that matches the local output of "uname -m" > to select it for further architecture-specific processing. I can easily > imagine myself writing such a thing. > > So, I confess "making it largely useless" was hyperbolic, but I still > think it's a bad idea.
Hmm. You're talking about why setting -wx on a /tmp is a bad thing: it will work but it may break some software trying to do ls /tmp, that's true. But Tom was asking why it's bad to set rw- which is much much worse because you need an x on a dir bit not to just cd but to access its contents in any way. Example: sal...@salmin:~$ mkdir dir sal...@salmin:~$ ls -ld dir drwxr-xr-x 2 salmin salmin 4096 May 24 11:01 dir sal...@salmin:~$ echo 123 > dir/a sal...@salmin:~$ cat dir/a 123 sal...@salmin:~$ chmod 111 dir sal...@salmin:~$ ls -ld dir d--x--x--x 2 salmin salmin 4096 May 24 11:01 dir sal...@salmin:~$ ls -l dir ls: cannot open directory dir: Permission denied sal...@salmin:~$ cat dir/a 123 x is set, r is not: can access dir/a but can't read dir contents sal...@salmin:~$ chmod 444 dir sal...@salmin:~$ ls -ld dir dr--r--r-- 2 salmin salmin 4096 May 24 11:01 dir sal...@salmin:~$ ls -l dir ls: cannot access dir/a: Permission denied total 0 -????????? ? ? ? ? ? a sal...@salmin:~$ cat dir/a cat: dir/a: Permission denied r is set, x is not: can read dir contents but can not access dir/a. That's way we can possibly set -wx on /tmp but setting rw- on any dir will make it completely unusable. Alexey -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/aanlktikr3nfnxsppr_6lbkvehslkrhxjmk7xdykdi...@mail.gmail.com
