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    SubjectRe: [PATCH] procfs: Prevent unpriveleged processes accessing fdinfo
    On Thu, Jul 8, 2021 at 8:57 AM Kalesh Singh <kaleshsingh@google.com> wrote:
    >
    > The file permissions on the fdinfo dir from were changed from
    > S_IRUSR|S_IXUSR to S_IRUGO|S_IXUGO, and a PTRACE_MODE_READ check was
    > added for opening the fdinfo files [1]. However, the ptrace permission
    > check was not added to the directory, allowing anyone to get the open FD
    > numbers by reading the fdinfo directory.
    >
    > Add the missing ptrace permission check for opening the fdinfo directory.

    The more I look at this, the more I feel like we should look at
    instead changing how "get_proc_task()" works.

    That's one of the core functions for /proc, and I wonder if we
    couldn't just make it refuse to look up a task that has gone through a
    suid execve() since the proc inode was opened.

    I don't think it's basically ever ok to open something for one thread,
    and then use it after the thread has gone through a suid thing.

    In fact, I wonder if we could make it even stricter, and go "any exec
    at all", but I think a suid exec might be the minimum we should do.

    Then the logic really becomes very simple: we did the permission
    checks at open time (like UNIX permission checks should be done), and
    "get_proc_task()" basically verifies that "yeah, that open-time
    decision is still valid".

    Wouldn't that make a lot of sense?

    Linus

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