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Subject[PATCH RFC v2] pidns: introduce syscall getvpid
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pid_t getvpid(pid_t pid, int source, int target);

This syscall converts pid from source pid-namespace into pid in target
pid-namespace. Namespaces are defined by file descriptors pointing to
namespace entries in proc (/proc/[pid]/ns/pid). If source / target is
negative then current pid namespace is used.

If pid is negative then getvpid() returns pid of parent task for -pid.

If pid is unreachable from target namespace then syscall returns zero.

Errors:
ESRCH task not found
EBADF closed file descriptor
EINVAL not pid-namespace file descriptor

Examples:
getvpid(pid, ns, -1) -> pid in our pid namespace
getvpid(pid, -1, ns) -> pid in container
getvpid(1, ns1, ns2) > 0 -> ns1 inside ns2
getvpid(1, ns1, ns2) == 0 -> ns1 outside ns2
getvpid(1, ns, -1) -> init task of pid-namespace
getvpid(-1, ns, -1) -> task in parent pid-namespace
getvpid(-pid, -1, -1) -> get ppid by pid

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

---

v2:
* use namespace-fd as second/third argument
* add -pid for getting parent pid
* move code into kernel/sys.c next to getppid
* drop ifdef CONFIG_PID_NS
* add generic syscall
---
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
include/linux/syscalls.h | 1 +
include/uapi/asm-generic/unistd.h | 4 ++
kernel/sys.c | 63 ++++++++++++++++++++++++++++++++
5 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 7663c455b9f6..dadb55d42fc9 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -382,3 +382,4 @@
373 i386 shutdown sys_shutdown
374 i386 userfaultfd sys_userfaultfd
375 i386 membarrier sys_membarrier
+376 i386 getvpid sys_getvpid
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 278842fdf1f6..0338f2eb3b7c 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -331,6 +331,7 @@
322 64 execveat stub_execveat
323 common userfaultfd sys_userfaultfd
324 common membarrier sys_membarrier
+325 common getvpid sys_getvpid

#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a460e2ef2843..01ac603c8b5c 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -222,6 +222,7 @@ asmlinkage long sys_nanosleep(struct timespec __user *rqtp, struct timespec __us
asmlinkage long sys_alarm(unsigned int seconds);
asmlinkage long sys_getpid(void);
asmlinkage long sys_getppid(void);
+asmlinkage long sys_getvpid(pid_t pid, int source, int target);
asmlinkage long sys_getuid(void);
asmlinkage long sys_geteuid(void);
asmlinkage long sys_getgid(void);
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 8da542a2874d..163df44b23cf 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -711,9 +711,11 @@ __SYSCALL(__NR_bpf, sys_bpf)
__SC_COMP(__NR_execveat, sys_execveat, compat_sys_execveat)
#define __NR_membarrier 282
__SYSCALL(__NR_membarrier, sys_membarrier)
+#define __NR_getvpid 283
+__SYSCALL(__NR_getvpid, sys_getvpid)

#undef __NR_syscalls
-#define __NR_syscalls 283
+#define __NR_syscalls 284

/*
* All syscalls below here should go away really,
diff --git a/kernel/sys.c b/kernel/sys.c
index fa2f2f671a5c..fbfe938dd9d7 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -46,6 +46,7 @@
#include <linux/syscalls.h>
#include <linux/kprobes.h>
#include <linux/user_namespace.h>
+#include <linux/proc_ns.h>
#include <linux/binfmts.h>

#include <linux/sched.h>
@@ -855,6 +856,68 @@ SYSCALL_DEFINE0(getppid)
return pid;
}

+SYSCALL_DEFINE3(getvpid, pid_t, pid, int, source, int, target)
+{
+ struct file *source_file = NULL, *target_file = NULL;
+ struct pid_namespace *source_ns, *target_ns;
+ struct pid *struct_pid;
+ struct ns_common *ns;
+ pid_t result;
+
+ if (source >= 0) {
+ source_file = proc_ns_fget(source);
+ result = PTR_ERR(source_file);
+ if (IS_ERR(source_file))
+ goto out;
+ ns = get_proc_ns(file_inode(source_file));
+ result = -EINVAL;
+ if (ns->ops->type != CLONE_NEWPID)
+ goto out;
+ source_ns = container_of(ns, struct pid_namespace, ns);
+ } else
+ source_ns = task_active_pid_ns(current);
+
+ if (target >= 0) {
+ target_file = proc_ns_fget(target);
+ result = PTR_ERR(target_file);
+ if (IS_ERR(target_file))
+ goto out;
+ ns = get_proc_ns(file_inode(target_file));
+ result = -EINVAL;
+ if (ns->ops->type != CLONE_NEWPID)
+ goto out;
+ target_ns = container_of(ns, struct pid_namespace, ns);
+ } else
+ target_ns = task_active_pid_ns(current);
+
+ rcu_read_lock();
+ struct_pid = find_pid_ns(abs(pid), source_ns);
+
+ if (struct_pid && pid < 0) {
+ struct task_struct *task;
+
+ task = pid_task(struct_pid, PIDTYPE_PID);
+ if (task)
+ task = rcu_dereference(task->real_parent);
+ struct_pid = task ? task_pid(task) : NULL;
+ }
+
+ if (struct_pid)
+ result = pid_nr_ns(struct_pid, target_ns);
+ else
+ result = -ESRCH;
+ rcu_read_unlock();
+
+out:
+ if (!IS_ERR_OR_NULL(target_file))
+ fput(target_file);
+
+ if (!IS_ERR_OR_NULL(source_file))
+ fput(source_file);
+
+ return result;
+}
+
SYSCALL_DEFINE0(getuid)
{
/* Only we change this so SMP safe */


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