Hi On Tue, Apr 22, 2014 at 8:58 PM, Pavel Machek <pavel@xxxxxx> wrote: > I don't think openat helps you. This is what we are talking about, it > is easy to reproduce. Can you reproduce it without /proc mounted? > > I think that chmod 700 . should stop you. Openat seems no worse than > just placing cwd there... Example1: $ mkdir -p subdir/next $ chmod 000 subdir $ touch subdir/next/test => EACCES $ cd subdir => EACCES Example2: $ mkdir -p subdir/next $ cd subdir/next $ chmod 000 .. $ touch test => SUCCESS This is the exact same situation. The filesystem tree is exactly the same in both situations, but in the first example CWD is outside of "subdir", in the second example CWD is inside of "subdir". Thus, they can create files in that directory, even though they have no access to _any_ absolute path to that directory. This is the exact same race that you describe via /proc/self/fd/. But instead of keeping a ref to the dir via CWD, in your example you keep the ref via a FD in that exact same directory and access it via /proc. (Hint: instead of using CWD, you can also keep an FD via open(O_PATH) and pass it to openat()) Thanks David -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
