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Message-ID: <20111013140216.GD11230@moon>
Date: Thu, 13 Oct 2011 18:02:16 +0400
From: Cyrill Gorcunov <gorcunov@...nvz.org>
To: LKML <linux-kernel@...r.kernel.org>, Nathan Lynch <ntl@...ox.com>,
Oren Laadan <orenl@...columbia.edu>,
Daniel Lezcano <dlezcano@...ibm.com>,
Serge Hallyn <serue@...ibm.com>, Tejun Heo <tj@...nel.org>
Cc: Pavel Emelyanov <xemul@...allels.com>,
Glauber Costa <glommer@...allels.com>,
Linux Containers <containers@...ts.osdl.org>,
James Bottomley <jbottomley@...allels.com>
Subject: [PATCH] clone: Introduce the CLONE_CHILD_USEPID functionality
At previous review session seems no final conclusion was made so this is
a second attempt to step forward.
---
From: Pavel Emelyanov <xemul@...nvz.org>
Subject: [PATCH] clone: Introduce the CLONE_CHILD_USEPID functionality
When restoring a task (or a set of tasks) we need to recreate them with
exactly the same pid as they had before. Thus we need the ability to create
a task with specified pid.
The proposal is to reuse the already free CLONE_STOPPED clone flag.
About the security implication - this can create some problems with pids
wraparound and similar, so this approach can be restricted with the "don't
allow for CLONE_CHILD_USEPID when the current pid namespace has ever done
real pid allocation". This will work perfectly for checkpoint-restore and
will not give anyone chances for screwing pids up on a living system.
Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
---
include/linux/pid.h | 2 -
include/linux/sched.h | 1
kernel/fork.c | 10 ++++++-
kernel/pid.c | 70 ++++++++++++++++++++++++++++++++++++--------------
4 files changed, 62 insertions(+), 21 deletions(-)
Index: linux-2.6.git/include/linux/pid.h
===================================================================
--- linux-2.6.git.orig/include/linux/pid.h
+++ linux-2.6.git/include/linux/pid.h
@@ -119,7 +119,7 @@ extern struct pid *find_get_pid(int nr);
extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
-extern struct pid *alloc_pid(struct pid_namespace *ns);
+extern struct pid *alloc_pid(struct pid_namespace *ns, int pid);
extern void free_pid(struct pid *pid);
/*
Index: linux-2.6.git/include/linux/sched.h
===================================================================
--- linux-2.6.git.orig/include/linux/sched.h
+++ linux-2.6.git/include/linux/sched.h
@@ -23,6 +23,7 @@
#define CLONE_CHILD_SETTID 0x01000000 /* set the TID in the child */
/* 0x02000000 was previously the unused CLONE_STOPPED (Start in stopped state)
and is now available for re-use. */
+#define CLONE_CHILD_USEPID 0x02000000 /* use the given pid */
#define CLONE_NEWUTS 0x04000000 /* New utsname group? */
#define CLONE_NEWIPC 0x08000000 /* New ipcs */
#define CLONE_NEWUSER 0x10000000 /* New user namespace */
Index: linux-2.6.git/kernel/fork.c
===================================================================
--- linux-2.6.git.orig/kernel/fork.c
+++ linux-2.6.git/kernel/fork.c
@@ -1239,8 +1239,16 @@ static struct task_struct *copy_process(
goto bad_fork_cleanup_io;
if (pid != &init_struct_pid) {
+ int want_pid = 0;
+
+ if (clone_flags & CLONE_CHILD_USEPID) {
+ retval = get_user(want_pid, child_tidptr);
+ if (retval)
+ goto bad_fork_cleanup_io;
+ }
+
retval = -ENOMEM;
- pid = alloc_pid(p->nsproxy->pid_ns);
+ pid = alloc_pid(p->nsproxy->pid_ns, want_pid);
if (!pid)
goto bad_fork_cleanup_io;
}
Index: linux-2.6.git/kernel/pid.c
===================================================================
--- linux-2.6.git.orig/kernel/pid.c
+++ linux-2.6.git/kernel/pid.c
@@ -159,11 +159,55 @@ static void set_last_pid(struct pid_name
} while ((prev != last_write) && (pid_before(base, last_write, pid)));
}
-static int alloc_pidmap(struct pid_namespace *pid_ns)
+static int alloc_pidmap_page(struct pidmap *map)
+{
+ if (unlikely(!map->page)) {
+ void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ /*
+ * Free the page if someone raced with us
+ * installing it:
+ */
+ spin_lock_irq(&pidmap_lock);
+ if (!map->page) {
+ map->page = page;
+ page = NULL;
+ }
+ spin_unlock_irq(&pidmap_lock);
+ kfree(page);
+ if (unlikely(!map->page))
+ return -ENOMEM;
+ }
+
+ return 0;
+}
+
+static int set_pidmap(struct pid_namespace *pid_ns, int pid)
+{
+ int offset;
+ struct pidmap *map;
+
+ offset = pid & BITS_PER_PAGE_MASK;
+ map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
+
+ if (alloc_pidmap_page(map) < 0)
+ return -ENOMEM;
+
+ if (!test_and_set_bit(offset, map->page)) {
+ atomic_dec(&map->nr_free);
+ return pid;
+ }
+
+ return -EBUSY;
+}
+
+static int alloc_pidmap(struct pid_namespace *pid_ns, int desired_pid)
{
int i, offset, max_scan, pid, last = pid_ns->last_pid;
struct pidmap *map;
+ if (desired_pid)
+ return set_pidmap(pid_ns, desired_pid);
+
pid = last + 1;
if (pid >= pid_max)
pid = RESERVED_PIDS;
@@ -176,22 +220,9 @@ static int alloc_pidmap(struct pid_names
*/
max_scan = DIV_ROUND_UP(pid_max, BITS_PER_PAGE) - !offset;
for (i = 0; i <= max_scan; ++i) {
- if (unlikely(!map->page)) {
- void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
- /*
- * Free the page if someone raced with us
- * installing it:
- */
- spin_lock_irq(&pidmap_lock);
- if (!map->page) {
- map->page = page;
- page = NULL;
- }
- spin_unlock_irq(&pidmap_lock);
- kfree(page);
- if (unlikely(!map->page))
- break;
- }
+ if (alloc_pidmap_page(map) < 0)
+ break;
+
if (likely(atomic_read(&map->nr_free))) {
do {
if (!test_and_set_bit(offset, map->page)) {
@@ -277,7 +308,7 @@ void free_pid(struct pid *pid)
call_rcu(&pid->rcu, delayed_put_pid);
}
-struct pid *alloc_pid(struct pid_namespace *ns)
+struct pid *alloc_pid(struct pid_namespace *ns, int this_ns_pid)
{
struct pid *pid;
enum pid_type type;
@@ -291,13 +322,14 @@ struct pid *alloc_pid(struct pid_namespa
tmp = ns;
for (i = ns->level; i >= 0; i--) {
- nr = alloc_pidmap(tmp);
+ nr = alloc_pidmap(tmp, this_ns_pid);
if (nr < 0)
goto out_free;
pid->numbers[i].nr = nr;
pid->numbers[i].ns = tmp;
tmp = tmp->parent;
+ this_ns_pid = 0;
}
get_pid_ns(ns);
--
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