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523cd85198
The patch "sysctl: Add the kernel.ns_last_pid control" is not yet handled by crtools, still it's staged here to not loose it and collect all Acks in place. Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
103 lines
3.5 KiB
Text
103 lines
3.5 KiB
Text
sysctl: Add the kernel.ns_last_pid control
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From: Pavel Emelyanov <xemul@parallels.com>
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The sysctl works on the current task's pid namespace, getting and setting its
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last_pid field.
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Writing is allowed for CAP_SYS_ADMIN-capable tasks thus making it possible to
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create a task with desired pid value. This ability is required badly for the
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checkpoint/restore in userspace.
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This approach suits all the parties for now.
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Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
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Acked-by: Tejun Heo <tj@kernel.org>
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CC: Oleg Nesterov <oleg@redhat.com>
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CC: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
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---
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Documentation/sysctl/kernel.txt | 8 ++++++++
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kernel/pid.c | 4 +++-
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kernel/pid_namespace.c | 31 +++++++++++++++++++++++++++++++
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3 files changed, 42 insertions(+), 1 deletion(-)
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Index: linux-2.6.git/Documentation/sysctl/kernel.txt
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===================================================================
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--- linux-2.6.git.orig/Documentation/sysctl/kernel.txt
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+++ linux-2.6.git/Documentation/sysctl/kernel.txt
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@@ -401,6 +401,14 @@ PIDs of value pid_max or larger are not
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==============================================================
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+ns_last_pid:
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+
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+The last pid allocated in the current (the one task using this sysctl
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+lives in) pid namespace. When selecting a pid for a next task on fork
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+kernel tries to allocate a number starting from this one.
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+
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+==============================================================
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+
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powersave-nap: (PPC only)
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If set, Linux-PPC will use the 'nap' mode of powersaving,
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Index: linux-2.6.git/kernel/pid.c
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===================================================================
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--- linux-2.6.git.orig/kernel/pid.c
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+++ linux-2.6.git/kernel/pid.c
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@@ -137,7 +137,9 @@ static int pid_before(int base, int a, i
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}
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/*
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- * We might be racing with someone else trying to set pid_ns->last_pid.
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+ * We might be racing with someone else trying to set pid_ns->last_pid
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+ * at the pid allocation time (there's also a sysctl for this, but racing
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+ * with this one is OK, see comment in kernel/pid_namespace.c about it).
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* We want the winner to have the "later" value, because if the
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* "earlier" value prevails, then a pid may get reused immediately.
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*
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Index: linux-2.6.git/kernel/pid_namespace.c
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===================================================================
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--- linux-2.6.git.orig/kernel/pid_namespace.c
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+++ linux-2.6.git/kernel/pid_namespace.c
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@@ -191,9 +191,40 @@ void zap_pid_ns_processes(struct pid_nam
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return;
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}
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+static int pid_ns_ctl_handler(struct ctl_table *table, int write,
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+ void __user *buffer, size_t *lenp, loff_t *ppos)
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+{
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+ struct ctl_table tmp = *table;
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+
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+ if (write && !capable(CAP_SYS_ADMIN))
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+ return -EPERM;
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+
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+ /*
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+ * Writing directly to ns' last_pid field is OK, since this field
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+ * is volatile in a living namespace anyway and a code writing to
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+ * it should synchronize its usage with external means.
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+ */
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+
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+ tmp.data = ¤t->nsproxy->pid_ns->last_pid;
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+ return proc_dointvec(&tmp, write, buffer, lenp, ppos);
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+}
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+
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+static struct ctl_table pid_ns_ctl_table[] = {
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+ {
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+ .procname = "ns_last_pid",
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+ .maxlen = sizeof(int),
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+ .mode = 0666, /* permissions are checked in the handler */
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+ .proc_handler = pid_ns_ctl_handler,
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+ },
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+ { }
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+};
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+
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+static struct ctl_path kern_path[] = { { .procname = "kernel", }, { } };
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+
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static __init int pid_namespaces_init(void)
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{
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pid_ns_cachep = KMEM_CACHE(pid_namespace, SLAB_PANIC);
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+ register_sysctl_paths(kern_path, pid_ns_ctl_table);
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return 0;
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}
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