Damn. I don't have time to read these patches today (will try tomorrow),
but when I glanced at this patch yesterday I had some suspicions...
On 07/26, Pavel Emelyanov wrote:
>
> +++ linux-2.6.23-rc1-mm1-7/kernel/signal.c 2007-07-26
> 16:36:37.000000000 +0400
> @@ -323,6 +325,9 @@ static int collect_signal(int sig, struc
> if (first) {
> list_del_init(&first->list);
> copy_siginfo(info, &first->info);
> + if (first->flags & SIGQUEUE_CINIT)
> + kinfo->flags |= KERN_SIGINFO_CINIT;
> +
>
> [...snip...]
>
> @@ -1852,7 +1950,7 @@ relock:
> * within that pid space. It can of course get signals from
> * its parent pid space.
> */
> - if (current == task_child_reaper(current))
> + if (kinfo.flags & KERN_SIGINFO_CINIT)
> continue;
I think the whole idea is broken, it assumes the sender put something into
"struct sigqueue".
Suppose that /sbin/init has no handler for (say) SIGTERM, and we send this
signal from the same namespace. send_signal() sets SIGQUEUE_CINIT, but it
is lost because __group_complete_signal() silently "converts" sig_fatal()
signals to SIGKILL using sigaddset().
> +static void encode_sender_info(struct task_struct *t, struct sigqueue *q)
> +{
> + /*
> + * If sender (i.e 'current') and receiver have the same active
> + * pid namespace and the receiver is the container-init, set the
> + * SIGQUEUE_CINIT flag. This tells the container-init that the
> + * signal originated in its own namespace and so it can choose
> + * to ignore the signal.
> + *
> + * If the receiver is the container-init of a pid namespace,
> + * but the sender is from an ancestor pid namespace, the
> + * container-init cannot ignore the signal. So clear the
> + * SIGQUEUE_CINIT flag in this case.
> + *
> + * Also, if the sender does not have a pid_t in the receiver's
> + * active pid namespace, set si_pid to 0 and pretend it originated
> + * from the kernel.
> + */
> + if (pid_ns_equal(t)) {
> + if (is_container_init(t)) {
> + q->flags |= SIGQUEUE_CINIT;
Ironically, this change carefully preserves the bug we already have :)
This doesn't protect init from "bad" signal if we send it to sub-thread
of init. Actually, this make the behaviour a bit worse compared to what
we currently have. Currently, at least the main init's thread survives
if we send SIGKILL to sub-thread.
> static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
> struct sigpending *signals)
> {
> @@ -710,6 +781,7 @@ static int send_signal(int sig, struct s
> copy_siginfo(&q->info, info);
> break;
> }
> + encode_sender_info(t, q);
We still send the signal if __sigqueue_alloc() fails. In that case, the
dequeued siginfo won't have SIGQUEUE_CINIT/KERN_SIGINFO_CINIT, not good.
> @@ -1158,6 +1232,13 @@ static int kill_something_info(int sig,
>
> read_lock(&tasklist_lock);
> for_each_process(p) {
> + /*
> + * System-wide signals apply only to the sender's
> + * pid namespace, unless issued from init_pid_ns.
> + */
> + if (!task_visible_in_pid_ns(p, my_ns))
> + continue;
> +
> if (p->pid > 1 && p->tgid != current->tgid) {
This "p->pid > 1" check should die.
> +static int deny_signal_to_container_init(struct task_struct *tsk, int sig)
> +{
> + /*
> + * If receiver is the container-init of sender and signal is SIGKILL
> + * reject it right-away. If signal is any other one, let the container
> + * init decide (in get_signal_to_deliver()) whether to handle it or
> + * ignore it.
> + */
> + if (is_container_init(tsk) && (sig == SIGKILL) && pid_ns_equal(tsk))
> + return -EPERM;
> +
> + return 0;
> +}
> +
> /*
> * Bad permissions for sending the signal
> */
> @@ -545,6 +584,10 @@ static int check_kill_permission(int sig
> && !capable(CAP_KILL))
> return error;
>
> + error = deny_signal_to_container_init(t, sig);
> + if (error)
> + return error;
Hm. Could you explain this change? Why do we need a special check for SIGKILL?
(What about ptrace_attach() btw? If it is possible to send a signal to init
from the "parent" namespace, perhaps it makes sense to allow ptracing as
well).
Oleg.
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