The main motivation to add set_tid to clone3() is CRIU.
To restore a process with the same PID/TID CRIU currently uses
/proc/sys/kernel/ns_last_pid. It writes the desired (PID - 1) to
ns_last_pid and then (quickly) does a clone(). This works most of the
time, but it is racy. It is also slow as it requires multiple syscalls.
Extending clone3() to support *set_tid makes it possible restore a
process using CRIU without accessing /proc/sys/kernel/ns_last_pid and
race free (as long as the desired PID/TID is available).
This clone3() extension places the same restrictions (CAP_SYS_ADMIN)
on clone3() with *set_tid as they are currently in place for ns_last_pid.
The original version of this change was using a single value for
set_tid. At the 2019 LPC, after presenting set_tid, it was, however,
decided to change set_tid to an array to enable setting the PID of a
process in multiple PID namespaces at the same time. If a process is
created in a PID namespace it is possible to influence the PID inside
and outside of the PID namespace. Details also in the corresponding
selftest.
To create a process with the following PIDs:
PID NS level Requested PID
0 (host) 31496
1 42
2 1
For that example the two newly introduced parameters to struct
clone_args (set_tid and set_tid_size) would need to be:
set_tid[0] = 1;
set_tid[1] = 42;
set_tid[2] = 31496;
set_tid_size = 3;
If only the PIDs of the two innermost nested PID namespaces should be
defined it would look like this:
set_tid[0] = 1;
set_tid[1] = 42;
set_tid_size = 2;
The PID of the newly created process would then be the next available
free PID in the PID namespace level 0 (host) and 42 in the PID namespace
at level 1 and the PID of the process in the innermost PID namespace
would be 1.
The set_tid array is used to specify the PID of a process starting
from the innermost nested PID namespaces up to set_tid_size PID namespaces.
set_tid_size cannot be larger then the current PID namespace level.
Signed-off-by: Adrian Reber <areber@redhat.com>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>
Acked-by: Andrei Vagin <avagin@gmail.com>
Link: https://lore.kernel.org/r/20191115123621.142252-1-areber@redhat.com
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
extern struct pid *find_get_pid(int nr);
extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
-extern struct pid *alloc_pid(struct pid_namespace *ns);
+extern struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
+ size_t set_tid_size);
extern void free_pid(struct pid *pid);
extern void disable_pid_allocation(struct pid_namespace *ns);
#include <linux/ns_common.h>
#include <linux/idr.h>
+/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
+#define MAX_PID_NS_LEVEL 32
struct fs_pin;
unsigned long stack;
unsigned long stack_size;
unsigned long tls;
+ pid_t *set_tid;
+ /* Number of elements in *set_tid */
+ size_t set_tid_size;
};
/*
#ifndef __ASSEMBLY__
/**
* struct clone_args - arguments for the clone3 syscall
- * @flags: Flags for the new process as listed above.
- * All flags are valid except for CSIGNAL and
- * CLONE_DETACHED.
- * @pidfd: If CLONE_PIDFD is set, a pidfd will be
- * returned in this argument.
- * @child_tid: If CLONE_CHILD_SETTID is set, the TID of the
- * child process will be returned in the child's
- * memory.
- * @parent_tid: If CLONE_PARENT_SETTID is set, the TID of
- * the child process will be returned in the
- * parent's memory.
- * @exit_signal: The exit_signal the parent process will be
- * sent when the child exits.
- * @stack: Specify the location of the stack for the
- * child process.
- * @stack_size: The size of the stack for the child process.
- * @tls: If CLONE_SETTLS is set, the tls descriptor
- * is set to tls.
+ * @flags: Flags for the new process as listed above.
+ * All flags are valid except for CSIGNAL and
+ * CLONE_DETACHED.
+ * @pidfd: If CLONE_PIDFD is set, a pidfd will be
+ * returned in this argument.
+ * @child_tid: If CLONE_CHILD_SETTID is set, the TID of the
+ * child process will be returned in the child's
+ * memory.
+ * @parent_tid: If CLONE_PARENT_SETTID is set, the TID of
+ * the child process will be returned in the
+ * parent's memory.
+ * @exit_signal: The exit_signal the parent process will be
+ * sent when the child exits.
+ * @stack: Specify the location of the stack for the
+ * child process.
+ * @stack_size: The size of the stack for the child process.
+ * @tls: If CLONE_SETTLS is set, the tls descriptor
+ * is set to tls.
+ * @set_tid: Pointer to an array of type *pid_t. The size
+ * of the array is defined using @set_tid_size.
+ * This array is used to select PIDs/TIDs for
+ * newly created processes. The first element in
+ * this defines the PID in the most nested PID
+ * namespace. Each additional element in the array
+ * defines the PID in the parent PID namespace of
+ * the original PID namespace. If the array has
+ * less entries than the number of currently
+ * nested PID namespaces only the PIDs in the
+ * corresponding namespaces are set.
+ * @set_tid_size: This defines the size of the array referenced
+ * in @set_tid. This cannot be larger than the
+ * kernel's limit of nested PID namespaces.
*
* The structure is versioned by size and thus extensible.
* New struct members must go at the end of the struct and
__aligned_u64 stack;
__aligned_u64 stack_size;
__aligned_u64 tls;
+ __aligned_u64 set_tid;
+ __aligned_u64 set_tid_size;
};
#endif
#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
+#define CLONE_ARGS_SIZE_VER1 80 /* sizeof second published struct */
/*
* Scheduling policies
stackleak_task_init(p);
if (pid != &init_struct_pid) {
- pid = alloc_pid(p->nsproxy->pid_ns_for_children);
+ pid = alloc_pid(p->nsproxy->pid_ns_for_children, args->set_tid,
+ args->set_tid_size);
if (IS_ERR(pid)) {
retval = PTR_ERR(pid);
goto bad_fork_cleanup_thread;
{
int err;
struct clone_args args;
+ pid_t *kset_tid = kargs->set_tid;
if (unlikely(usize > PAGE_SIZE))
return -E2BIG;
if (err)
return err;
+ if (unlikely(args.set_tid_size > MAX_PID_NS_LEVEL))
+ return -EINVAL;
+
+ if (unlikely(!args.set_tid && args.set_tid_size > 0))
+ return -EINVAL;
+
+ if (unlikely(args.set_tid && args.set_tid_size == 0))
+ return -EINVAL;
+
/*
* Verify that higher 32bits of exit_signal are unset and that
* it is a valid signal
.stack = args.stack,
.stack_size = args.stack_size,
.tls = args.tls,
+ .set_tid_size = args.set_tid_size,
};
+ if (args.set_tid &&
+ copy_from_user(kset_tid, u64_to_user_ptr(args.set_tid),
+ (kargs->set_tid_size * sizeof(pid_t))))
+ return -EFAULT;
+
+ kargs->set_tid = kset_tid;
+
return 0;
}
int err;
struct kernel_clone_args kargs;
+ pid_t set_tid[MAX_PID_NS_LEVEL];
+
+ kargs.set_tid = set_tid;
err = copy_clone_args_from_user(&kargs, uargs, size);
if (err)
call_rcu(&pid->rcu, delayed_put_pid);
}
-struct pid *alloc_pid(struct pid_namespace *ns)
+struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
+ size_t set_tid_size)
{
struct pid *pid;
enum pid_type type;
struct upid *upid;
int retval = -ENOMEM;
+ /*
+ * set_tid_size contains the size of the set_tid array. Starting at
+ * the most nested currently active PID namespace it tells alloc_pid()
+ * which PID to set for a process in that most nested PID namespace
+ * up to set_tid_size PID namespaces. It does not have to set the PID
+ * for a process in all nested PID namespaces but set_tid_size must
+ * never be greater than the current ns->level + 1.
+ */
+ if (set_tid_size > ns->level + 1)
+ return ERR_PTR(-EINVAL);
+
pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
if (!pid)
return ERR_PTR(retval);
pid->level = ns->level;
for (i = ns->level; i >= 0; i--) {
- int pid_min = 1;
+ int tid = 0;
+
+ if (set_tid_size) {
+ tid = set_tid[ns->level - i];
+
+ retval = -EINVAL;
+ if (tid < 1 || tid >= pid_max)
+ goto out_free;
+ /*
+ * Also fail if a PID != 1 is requested and
+ * no PID 1 exists.
+ */
+ if (tid != 1 && !tmp->child_reaper)
+ goto out_free;
+ retval = -EPERM;
+ if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
+ goto out_free;
+ set_tid_size--;
+ }
idr_preload(GFP_KERNEL);
spin_lock_irq(&pidmap_lock);
- /*
- * init really needs pid 1, but after reaching the maximum
- * wrap back to RESERVED_PIDS
- */
- if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
- pid_min = RESERVED_PIDS;
-
- /*
- * Store a null pointer so find_pid_ns does not find
- * a partially initialized PID (see below).
- */
- nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
- pid_max, GFP_ATOMIC);
+ if (tid) {
+ nr = idr_alloc(&tmp->idr, NULL, tid,
+ tid + 1, GFP_ATOMIC);
+ /*
+ * If ENOSPC is returned it means that the PID is
+ * alreay in use. Return EEXIST in that case.
+ */
+ if (nr == -ENOSPC)
+ nr = -EEXIST;
+ } else {
+ int pid_min = 1;
+ /*
+ * init really needs pid 1, but after reaching the
+ * maximum wrap back to RESERVED_PIDS
+ */
+ if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
+ pid_min = RESERVED_PIDS;
+
+ /*
+ * Store a null pointer so find_pid_ns does not find
+ * a partially initialized PID (see below).
+ */
+ nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
+ pid_max, GFP_ATOMIC);
+ }
spin_unlock_irq(&pidmap_lock);
idr_preload_end();
static DEFINE_MUTEX(pid_caches_mutex);
static struct kmem_cache *pid_ns_cachep;
-/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
-#define MAX_PID_NS_LEVEL 32
/* Write once array, filled from the beginning. */
static struct kmem_cache *pid_cache[MAX_PID_NS_LEVEL];
projects / openwrt / staging / blogic.git / commitdiff