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    Subject[PATCH] Forbid invocation of kexec_load() outside initial PID namespace
    Date
    From: "Daniel P. Berrange" <berrange@redhat.com>

    The following commit

    commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
    Author: Daniel Lezcano <daniel.lezcano@free.fr>
    Date: Wed Mar 28 14:42:51 2012 -0700

    pidns: add reboot_pid_ns() to handle the reboot syscall

    introduced custom handling of the reboot() syscall when invoked
    from a non-initial PID namespace. The intent was that a process
    in a container can be allowed to keep CAP_SYS_BOOT and execute
    reboot() to shutdown/reboot just their private container, rather
    than the host.

    Unfortunately the kexec_load() syscall also relies on the
    CAP_SYS_BOOT capability. So by allowing a container to keep
    this capability to safely invoke reboot(), they mistakenly
    also gain the ability to use kexec_load(). The solution is
    to make kexec_load() return -EPERM if invoked from a PID
    namespace that is not the initial namespace

    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
    Cc: Serge Hallyn <serge.hallyn@canonical.com>
    Cc: Daniel Lezcano <daniel.lezcano@free.fr>
    Cc: Michael Kerrisk <mtk.manpages@gmail.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Oleg Nesterov <oleg@redhat.com>
    ---
    kernel/kexec.c | 5 +++++
    1 file changed, 5 insertions(+)

    diff --git a/kernel/kexec.c b/kernel/kexec.c
    index 0668d58..b152bde 100644
    --- a/kernel/kexec.c
    +++ b/kernel/kexec.c
    @@ -947,6 +947,11 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
    if (!capable(CAP_SYS_BOOT))
    return -EPERM;

    + /* Processes in containers must not be allowed to load a new
    + * kernel, even if they have CAP_SYS_BOOT */
    + if (task_active_pid_ns(current) != &init_pid_ns)
    + return -EPERM;
    +
    /*
    * Verify we have a legal set of flags
    * This leaves us room for future extensions.
    --
    1.7.11.2


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