[PATCH 03/05]
This patch uses the value written into the next_syscall_data proc file
as a target upid nr for the next process to be created.
The following syscalls have a new behavior if next_syscall_data is set:
. fork()
. vfork()
. clone()
In the current version, if the process belongs to nested namespaces, only
the upper namespace level upid nr is allowed to be predefined, since there
is not yet a way to take a snapshot of upid nrs at all namespaces levels.
But this can easily be extended in the future.
Signed-off-by: Nadia Derbey <[EMAIL PROTECTED]>
---
include/linux/next_syscall_data.h | 2
kernel/fork.c | 5 -
kernel/pid.c | 116 +++++++++++++++++++++++++++++++-------
3 files changed, 102 insertions(+), 21 deletions(-)
Index: linux-2.6.26-rc8-mm1/kernel/pid.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/kernel/pid.c 2008-07-08 12:12:39.000000000
+0200
+++ linux-2.6.26-rc8-mm1/kernel/pid.c 2008-07-08 12:24:04.000000000 +0200
@@ -122,6 +122,26 @@ static void free_pidmap(struct upid *upi
atomic_inc(&map->nr_free);
}
+static inline 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)
+ kfree(page);
+ else
+ map->page = page;
+ spin_unlock_irq(&pidmap_lock);
+ if (unlikely(!map->page))
+ return -1;
+ }
+ return 0;
+}
+
static int alloc_pidmap(struct pid_namespace *pid_ns)
{
int i, offset, max_scan, pid, last = pid_ns->last_pid;
@@ -134,21 +154,8 @@ static int alloc_pidmap(struct pid_names
map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
max_scan = (pid_max + BITS_PER_PAGE - 1)/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)
- kfree(page);
- else
- map->page = page;
- spin_unlock_irq(&pidmap_lock);
- if (unlikely(!map->page))
- break;
- }
+ if (unlikely(alloc_pidmap_page(map)))
+ break;
if (likely(atomic_read(&map->nr_free))) {
do {
if (!test_and_set_bit(offset, map->page)) {
@@ -182,6 +189,33 @@ static int alloc_pidmap(struct pid_names
return -1;
}
+/*
+ * Return 0 if successful (i.e. next_nr could be assigned as a upid nr).
+ * -errno else
+ */
+static int alloc_fixed_pidmap(struct pid_namespace *pid_ns, int next_nr)
+{
+ int offset;
+ struct pidmap *map;
+
+ if (next_nr < RESERVED_PIDS || next_nr >= pid_max)
+ return -EINVAL;
+
+ map = &pid_ns->pidmap[next_nr / BITS_PER_PAGE];
+
+ if (unlikely(alloc_pidmap_page(map)))
+ return -ENOMEM;
+
+ offset = next_nr & BITS_PER_PAGE_MASK;
+ if (test_and_set_bit(offset, map->page))
+ return -EBUSY;
+
+ atomic_dec(&map->nr_free);
+ pid_ns->last_pid = max(pid_ns->last_pid, next_nr);
+
+ return 0;
+}
+
int next_pidmap(struct pid_namespace *pid_ns, int last)
{
int offset;
@@ -239,6 +273,24 @@ void free_pid(struct pid *pid)
call_rcu(&pid->rcu, delayed_put_pid);
}
+/*
+ * Sets a predefined upid nr for the process' upper namespace level
+ */
+static int set_predefined_pid(struct pid_namespace *ns, struct pid *pid,
+ int next_nr)
+{
+ int i = ns->level;
+ int rc;
+
+ rc = alloc_fixed_pidmap(ns, next_nr);
+ if (rc < 0)
+ return rc;
+
+ pid->numbers[i].nr = next_nr;
+ pid->numbers[i].ns = ns;
+ return 0;
+}
+
struct pid *alloc_pid(struct pid_namespace *ns)
{
struct pid *pid;
@@ -248,14 +300,41 @@ struct pid *alloc_pid(struct pid_namespa
struct upid *upid;
pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
- if (!pid)
+ if (!pid) {
+ pid = ERR_PTR(-ENOMEM);
goto out;
+ }
tmp = ns;
- for (i = ns->level; i >= 0; i--) {
+ i = ns->level;
+ if (unlikely(next_data_set(current))) {
+ /*
+ * There is a upid nr specified, use it instead of letting
+ * the kernel chose it for us.
+ */
+ int next_nr = get_next_data(current);
+ int rc;
+
+ reset_next_syscall_data(current);
+ rc = set_predefined_pid(tmp, pid, next_nr);
+ if (rc < 0) {
+ pid = ERR_PTR(rc);
+ goto out_free;
+ }
+ /* Go up one level */
+ tmp = tmp->parent;
+ i--;
+ }
+
+ /*
+ * Let the lower levels upid nrs be automatically allocated
+ */
+ for ( ; i >= 0; i--) {
nr = alloc_pidmap(tmp);
- if (nr < 0)
+ if (nr < 0) {
+ pid = ERR_PTR(-ENOMEM);
goto out_free;
+ }
pid->numbers[i].nr = nr;
pid->numbers[i].ns = tmp;
@@ -284,7 +363,6 @@ out_free:
free_pidmap(pid->numbers + i);
kmem_cache_free(ns->pid_cachep, pid);
- pid = NULL;
goto out;
}
Index: linux-2.6.26-rc8-mm1/kernel/fork.c
===================================================================
--- linux-2.6.26-rc8-mm1.orig/kernel/fork.c 2008-07-08 12:12:39.000000000
+0200
+++ linux-2.6.26-rc8-mm1/kernel/fork.c 2008-07-08 12:22:47.000000000 +0200
@@ -1118,10 +1118,11 @@ static struct task_struct *copy_process(
goto bad_fork_cleanup_io;
if (pid != &init_struct_pid) {
- retval = -ENOMEM;
pid = alloc_pid(task_active_pid_ns(p));
- if (!pid)
+ if (IS_ERR(pid)) {
+ retval = PTR_ERR(pid);
goto bad_fork_cleanup_io;
+ }
if (clone_flags & CLONE_NEWPID) {
retval = pid_ns_prepare_proc(task_active_pid_ns(p));
Index: linux-2.6.26-rc8-mm1/include/linux/next_syscall_data.h
===================================================================
--- linux-2.6.26-rc8-mm1.orig/include/linux/next_syscall_data.h 2008-07-08
12:12:39.000000000 +0200
+++ linux-2.6.26-rc8-mm1/include/linux/next_syscall_data.h 2008-07-08
12:22:47.000000000 +0200
@@ -5,6 +5,7 @@
* following is supported today:
* . object creation with a predefined id
* . for a sysv ipc object
+ * . for a process
*/
#ifndef _LINUX_NEXT_SYSCALL_DATA_H
@@ -18,6 +19,7 @@
* For example, it can be used to pre-set the id of the object to be created
* by next syscall. The following syscalls support this feature:
* . msgget(), semget(), shmget()
+ * . fork(), vfork(), clone()
*/
struct next_syscall_data {
int ndata;
--
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