pid_t getvpid(pid_t pid, int source, int target); This syscall converts pid from source pid-namespace into pid visible in target pid-namespace. If pid is unreachable from target namespace then getvpid() returns zero. Namespaces are defined by file descriptors pointing to entries in proc (/proc/[pid]/ns/pid). If argument is negative then current pid namespace is used. If pid is negative then getvpid() returns pid of parent task for -pid. Possible error codes: ESRCH - task not found EBADF - closed file descriptor EINVAL - not pid-namespace file descriptor Such conversion is required for interaction between processes from different pid-namespaces. For example system service at host system who provide access to restricted set of privileged operations for clients from containers have to convert pids back and forward. Recent kernels expose virtual pids in /proc/[pid]/status:NSpid, but this interface works only in one way and even that is non-trivial. Other option is passing pids with credentials via unix socket, but this solution requires a lot of preparation and CAP_SYS_ADMIN for sending arbitrary pids. This syscall works in both directions, it's fast and simple. Examples: getvpid(pid, ns, -1) - get pid in our pid namespace getvpid(pid, -1, ns) - get pid in container getvpid(pid, -1, ns) > 0 - is pid is reachable from container? getvpid(1, ns1, ns2) > 0 - is ns1 inside ns2? getvpid(1, ns1, ns2) == 0 - is ns1 outside ns2? getvpid(1, ns, -1) - get init task of pid-namespace getvpid(-1, ns, -1) - get reaper of init task in parent pid-namespace getvpid(-pid, -1, -1) - get ppid by pid Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx> -- v1: https://lkml.org/lkml/2015/9/15/411 v2: https://lkml.org/lkml/2015/9/24/278 v3: * use proc_ns_fdget() * update description * rebase to next-20150925 * fix conflict with mlock2 --- 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 | 51 ++++++++++++++++++++++++++++++++ 5 files changed, 57 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 143ef9f37932..c36c2c65d204 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -383,3 +383,4 @@ 374 i386 userfaultfd sys_userfaultfd 375 i386 membarrier sys_membarrier 376 i386 mlock2 sys_mlock2 +377 i386 getvpid sys_getvpid diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index 314a90bfc09c..90bbbc7fdbe0 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -332,6 +332,7 @@ 323 common userfaultfd sys_userfaultfd 324 common membarrier sys_membarrier 325 common mlock2 sys_mlock2 +326 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 a156b82dd14c..dbb5638260b5 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 1324b0292ec2..2c1123130f90 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -715,9 +715,11 @@ __SYSCALL(__NR_userfaultfd, sys_userfaultfd) __SYSCALL(__NR_membarrier, sys_membarrier) #define __NR_mlock2 284 __SYSCALL(__NR_mlock2, sys_mlock2) +#define __NR_mlock2 285 +__SYSCALL(__NR_getvpid, sys_getvpid) #undef __NR_syscalls -#define __NR_syscalls 285 +#define __NR_syscalls 286 /* * All syscalls below here should go away really, diff --git a/kernel/sys.c b/kernel/sys.c index fa2f2f671a5c..1e28a36b84fa 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 +856,56 @@ SYSCALL_DEFINE0(getppid) return pid; } +SYSCALL_DEFINE3(getvpid, pid_t, pid, int, source, int, target) +{ + struct pid_namespace *source_ns, *target_ns; + struct fd source_fd = {}, target_fd = {}; + struct pid *struct_pid; + struct ns_common *ns; + pid_t result; + + if (source >= 0) { + ns = proc_ns_fdget(source, CLONE_NEWPID, &source_fd); + result = PTR_ERR(ns); + if (IS_ERR(ns)) + goto out; + source_ns = container_of(ns, struct pid_namespace, ns); + } else + source_ns = task_active_pid_ns(current); + + if (target >= 0) { + ns = proc_ns_fdget(target, CLONE_NEWPID, &target_fd); + result = PTR_ERR(ns); + if (IS_ERR(ns)) + 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: + fdput(target_fd); + fdput(source_fd); + return result; +} + SYSCALL_DEFINE0(getuid) { /* Only we change this so SMP safe */ -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
