Re: [PATCH RFC v2] pidns: introduce syscall getvpid

[Chen Fan <chen.fan.fnst@cn.fujitsu.com>]

On 09/24/2015 09:53 PM, Konstantin Khlebnikov wrote:
> 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);
> +
the source ns and target ns translation looks the same, why not extract
a new method to do the job.

Thanks,
Chen
> +	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 */
>
> .
>