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    SubjectRe: [PATCH v18 01/15] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs
    From
    On Thu, Apr 12, 2012 at 2:47 PM, Will Drewry <wad@chromium.org> wrote:
    > From: Andy Lutomirski <luto@amacapital.net>
    >
    > With this change, calling
    >  prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)
    > disables privilege granting operations at execve-time.  For example, a
    > process will not be able to execute a setuid binary to change their uid
    > or gid if this bit is set.  The same is true for file capabilities.
    >
    > Additionally, LSM_UNSAFE_NO_NEW_PRIVS is defined to ensure that
    > LSMs respect the requested behavior.
    >
    > To determine if the NO_NEW_PRIVS bit is set, a task may call
    >  prctl(PR_GET_NO_NEW_PRIVS, 0, 0, 0, 0);
    > It returns 1 if set and 0 if it is not set. If any of the arguments are
    > non-zero, it will return -1 and set errno to -EINVAL.
    > (PR_SET_NO_NEW_PRIVS behaves similarly.)
    >
    > This functionality is desired for the proposed seccomp filter patch
    > series.  By using PR_SET_NO_NEW_PRIVS, it allows a task to modify the
    > system call behavior for itself and its child tasks without being
    > able to impact the behavior of a more privileged task.
    >
    > Another potential use is making certain privileged operations
    > unprivileged.  For example, chroot may be considered "safe" if it cannot
    > affect privileged tasks.
    >
    > Note, this patch causes execve to fail when PR_SET_NO_NEW_PRIVS is
    > set and AppArmor is in use.  It is fixed in a subsequent patch.
    >
    > Signed-off-by: Andy Lutomirski <luto@amacapital.net>
    > Signed-off-by: Will Drewry <wad@chromium.org>
    > Acked-by: Eric Paris <eparis@redhat.com>

    Acked-by: Kees Cook <keescook@chromium.org>

    --
    Kees Cook
    ChromeOS Security
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