Re: new ...at() flag: AT_NO_JUMPS

[Linus Torvalds]

On Thu, May 4, 2017 at 7:47 PM, Jann Horn <jannh@xxxxxxxxxx> wrote:
>
> Thread 1 starts an AT_BENEATH path walk using an O_PATH fd
> pointing to /srv/www/example.org/foo; the path given to the syscall is
> "bar/../../../../etc/passwd". The path walk enters the "bar" directory.
> Thread 2 moves /srv/www/example.org/foo/bar to
> /srv/www/example.org/bar.
> Thread 1 processes the rest of the path ("../../../../etc/passwd"), never
> hitting /srv/www/example.org/foo in the process.
>
> I'm not really familiar with the VFS internals, but from a coarse look
> at the patch, it seems like it wouldn't block this?

I think you're right.

I guess it would be safe for the RCU case due to the sequence number
check, but not the non-RCU case.

Al?

                 Linus