[RFC][PATCH 3/5] Determine if sender is from ancestor ns

Sukadev Bhattiprolu
2008-11-26T03:46:38Z

>From 95ae5f7dfaa77158b07d2cbdc8e5df0a81c93194 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Tue, 18 Nov 2008 16:55:06 -0800
Subject: [PATCH 3/5] Determine if sender is from ancestor ns

To implement container-init semantics, send_signal() must compute the pid
namespace of the sender, but since signals may originate in workqueues/
interrupt handlers, computing the namespace of sender is not always
possible/safe.

Define a flag, SIG_FROM_USER and set this flag when a signal originates
from user-space (i.e in kill(), tkill(), rt_sigqueueinfo()). When this
flag is set, send_signal() can safely compute the pid namespace of the
sender.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
kernel/signal.c | 35 ++++++++++++++++++++++++++++++++---
1 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index d8d20d6..45aebf0 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -793,14 +793,42 @@ static inline int legacy_queue(struct sigpending *signals, int sig)
return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);
}

+/*
+ * Return 1 if this signal originated directly from a user process (i.e via
+ * kill(), tkill(), sigqueue()) that is in an ancestor pid namespace of @t.
+ * Return 0 otherwise.
+ */
+#ifdef CONFIG_PID_NS
+#define SIG_FROM_USER INT_MIN /* MSB */
+static inline int siginfo_from_ancestor_ns(struct task_struct *t,
+ siginfo_t *info)
+{
+ if (!is_si_special(info) && (info->si_signo & SIG_FROM_USER)) {
+ /* if t can't see us we are from parent ns */
+ if (task_pid_nr_ns(current, task_active_pid_ns(t)) <= 0)
+ return 1;
+ }
+ return 0;
+}
+#else
+static inline int siginfo_from_ancestor_ns(struct task_struct *t,
+ siginfo_t *info)
+{
+ return 0;
+}
+#endif
+
static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
int group)
{
struct sigpending *pending;
struct sigqueue *q;
+ int from_ancestor_ns;

trace_sched_signal_send(sig, t);

+ from_ancestor_ns = siginfo_from_ancestor_ns(t, info);
+
assert_spin_locked(&t->sighand->siglock);
if (!prepare_signal(sig, t))
return 0;
@@ -850,6 +878,7 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
break;
default:
copy_siginfo(&q->info, info);
+ q->info.si_signo &= ~SIG_FROM_USER;
break;
}
} else if (!is_si_special(info)) {
@@ -2202,7 +2231,7 @@ sys_kill(pid_t pid, int sig)
{
struct siginfo info;

- info.si_signo = sig;
+ info.si_signo = sig | SIG_FROM_USER;
info.si_errno = 0;
info.si_code = SI_USER;
info.si_pid = task_tgid_vnr(current);
@@ -2219,7 +2248,7 @@ static int do_tkill(pid_t tgid, pid_t pid, int sig)
unsigned long flags;

error = -ESRCH;
- info.si_signo = sig;
+ info.si_signo = sig | SIG_FROM_USER;
info.si_errno = 0;
info.si_code = SI_TKILL;
info.si_pid = task_tgid_vnr(current);
@@ -2291,7 +2320,7 @@ sys_rt_sigqueueinfo(pid_t pid, int sig, siginfo_t __user *uinfo)
Nor can they impersonate a kill(), which adds source info. */
if (info.si_code >= 0)
return -EPERM;
- info.si_signo = sig;
+ info.si_signo = sig | SIG_FROM_USER;

/* POSIX.1b doesn't mention process groups. */
return kill_proc_info(sig, &info, pid);
--
1.5.2.5