Re: [PATCH] proc: make proc_fd_permission() thread-friendly

[Eric W. Biederman]

Oleg Nesterov <oleg@xxxxxxxxxx> writes:

> proc_fd_permission() says "process can still access /proc/self/fd
> after it has executed a setuid()", but the "task_pid() = proc_pid()
> check only helps if the task is group leader, /proc/self points to
> /proc/leader-pid.
>
> Change this check to use task_tgid() so that the whole process can
> access /proc/self/fd.

There is at least a semantic goofiness here.

There is /proc/<tgid>/fd and /proc/<tgid>/task/<pid>/fd, and the same
permission check is used by both.

We might just want to have a /proc/thread symlink as well so people
don't have this issue.  Of course that would require people to use it,
and I think the common case if people care is call gettid() and build
the path themselves.

Eric
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