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SubjectRe: [PATCH v4] pidns: introduce syscall translate_pid
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On 13.10.2017 12:26, Konstantin Khlebnikov wrote:
> pid_t translate_pid(pid_t pid, int source, int target);
>
> This syscall converts pid from source pid-ns into pid in target pid-ns.
> If pid is unreachable from target pid-ns it returns zero.
>
> Pid-namespaces are referred file descriptors opened to proc files
> /proc/[pid]/ns/pid or /proc/[pid]/ns/pid_for_children. Negative argument
> refers to current pid namespace, same as file /proc/self/ns/pid.
>
> Kernel expose virtual pids in /proc/[pid]/status:NSpid, but backward
> translation requires scanning all tasks. Also pids could be translated
> by sending them through unix socket between namespaces, this method is
> slow and insecure because other side is exposed inside pid namespace.
>
> Examples:
> translate_pid(pid, ns, -1) - get pid in our pid namespace
> translate_pid(pid, -1, ns) - get pid in other pid namespace
> translate_pid(1, ns, -1) - get pid of init task for namespace
> translate_pid(pid, -1, ns) > 0 - is pid is reachable from ns?
> translate_pid(1, ns1, ns2) > 0 - is ns1 inside ns2?
> translate_pid(1, ns1, ns2) == 0 - is ns1 outside ns2?
> translate_pid(1, ns1, ns2) == 1 - is ns1 equal ns2?
>
> Error codes:
> EBADF - file descriptor is closed
> EINVAL - file descriptor isn't pid-namespace
> ESRCH - task not found in @source namespace
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>
> ---
>
> v1: https://lkml.org/lkml/2015/9/15/411
> v2: https://lkml.org/lkml/2015/9/24/278
> * 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
> v3: https://lkml.org/lkml/2015/9/28/3
> * use proc_ns_fdget()
> * update description
> * rebase to next-20150925
> * fix conflict with mlock2
> v4:
> * rename into translate_pid()
> * remove syscall if CONFIG_PID_NS=n
> * drop -pid for parent task
> * drop fget-fdget optimizations
> * add helper get_pid_ns_by_fd()
> * wire only into x86
> ---
> arch/x86/entry/syscalls/syscall_32.tbl | 1
> arch/x86/entry/syscalls/syscall_64.tbl | 1
> include/linux/syscalls.h | 1
> kernel/pid_namespace.c | 66 ++++++++++++++++++++++++++++++++
> kernel/sys_ni.c | 3 +
> 5 files changed, 72 insertions(+)
>
> diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
> index 448ac2161112..257d839b3a91 100644
> --- a/arch/x86/entry/syscalls/syscall_32.tbl
> +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> @@ -391,3 +391,4 @@
> 382 i386 pkey_free sys_pkey_free
> 383 i386 statx sys_statx
> 384 i386 arch_prctl sys_arch_prctl compat_sys_arch_prctl
> +385 i386 translate_pid sys_translate_pid
> diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> index 5aef183e2f85..1ebdab83c6f4 100644
> --- a/arch/x86/entry/syscalls/syscall_64.tbl
> +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> @@ -339,6 +339,7 @@
> 330 common pkey_alloc sys_pkey_alloc
> 331 common pkey_free sys_pkey_free
> 332 common statx sys_statx
> +333 common translate_pid sys_translate_pid
>
> #
> # 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 a78186d826d7..6467ebc847c5 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -901,6 +901,7 @@ asmlinkage long sys_open_by_handle_at(int mountdirfd,
> struct file_handle __user *handle,
> int flags);
> asmlinkage long sys_setns(int fd, int nstype);
> +asmlinkage long sys_translate_pid(pid_t pid, int source, int target);
> asmlinkage long sys_process_vm_readv(pid_t pid,
> const struct iovec __user *lvec,
> unsigned long liovcnt,
> diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> index 4918314893bc..062f35eedd41 100644
> --- a/kernel/pid_namespace.c
> +++ b/kernel/pid_namespace.c
> @@ -13,6 +13,7 @@
> #include <linux/user_namespace.h>
> #include <linux/syscalls.h>
> #include <linux/cred.h>
> +#include <linux/file.h>
> #include <linux/err.h>
> #include <linux/acct.h>
> #include <linux/slab.h>
> @@ -406,6 +407,71 @@ static void pidns_put(struct ns_common *ns)
> put_pid_ns(to_pid_ns(ns));
> }
>
> +static struct pid_namespace *get_pid_ns_by_fd(int fd)
> +{
> + struct pid_namespace *pidns;
> + struct ns_common *ns;
> + struct file *file;
> +
> + file = proc_ns_fget(fd);
> + if (IS_ERR(file))
> + return ERR_CAST(file);
> +
> + ns = get_proc_ns(file_inode(file));
> + if (ns->ops->type == CLONE_NEWPID)
> + pidns = get_pid_ns(to_pid_ns(ns));
> + else
> + pidns = ERR_PTR(-EINVAL);
> +
> + fput(file);
> + return pidns;
> +}
> +
> +/*
> + * translate_pid - convert pid in source pid-ns into target pid-ns.
> + * @pid: pid for translation
> + * @source: pid-ns file descriptor or -1 for active namespace
> + * @target: pid-ns file descriptor or -1 for active namesapce
> + *
> + * Returns pid in @target pid-ns, zero if task have no pid there,
> + * or -ESRCH if task with @pid does not found in @source pid-ns.
> + */
> +SYSCALL_DEFINE3(translate_pid, pid_t, pid, int, source, int, target)
> +{
> + struct pid_namespace *source_ns, *target_ns;
> + struct pid *struct_pid;
> + pid_t result;
> +
> + if (source >= 0) {
> + source_ns = get_pid_ns_by_fd(source);
> + result = PTR_ERR(source_ns);
> + if (IS_ERR(source_ns))
> + goto err_source;
> + } else
> + source_ns = task_active_pid_ns(current);
> +
> + if (target >= 0) {
> + target_ns = get_pid_ns_by_fd(target);
> + result = PTR_ERR(target_ns);
> + if (IS_ERR(target_ns))
> + goto err_target;
> + } else
> + target_ns = task_active_pid_ns(current);
> +
> + rcu_read_lock();
> + struct_pid = find_pid_ns(pid, source_ns);
> + result = struct_pid ? pid_nr_ns(struct_pid, target_ns) : -ESRCH;
> + rcu_read_unlock();
> +
> + if (target >= 0)
> + put_pid_ns(target_ns);
> +err_target:
> + if (source >= 0)
> + put_pid_ns(source_ns);
> +err_source:
> + return result;
> +}
> +
> static int pidns_install(struct nsproxy *nsproxy, struct ns_common *ns)
> {
> struct pid_namespace *active = task_active_pid_ns(current);
> diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
> index 8acef8576ce9..1ca2a4c1eb1d 100644
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -258,3 +258,6 @@ cond_syscall(sys_membarrier);
> cond_syscall(sys_pkey_mprotect);
> cond_syscall(sys_pkey_alloc);
> cond_syscall(sys_pkey_free);
> +
> +/* pid namespace */
> +cond_syscall(sys_translate_pid);
>
#define _GNU_SOURCE
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <err.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

#ifndef SYS_translate_pid
#ifdef __x86_64__
#define SYS_translate_pid 333
#endif
#endif

pid_t translate_pid(pid_t pid, int source, int target) {
return syscall(SYS_translate_pid, pid, source, target);
}

int main(int argc, char **argv) {
int pid, source, target;
char buf[64];

if (argc != 4)
errx(1, "usage: %s <pid> <source|-1> <traget|-1>", argv[0]);

pid = atoi(argv[1]);
source = atoi(argv[2]);
target = atoi(argv[3]);

if (source >= 0) {
sprintf(buf, "/proc/%d/ns/pid", source);
source = open(buf, O_RDONLY);
if (source < 0)
err(2, "source %s", buf);
}

if (target >= 0) {
sprintf(buf, "/proc/%d/ns/pid", target);
target = open(buf, O_RDONLY);
if (target < 0)
err(2, "target %s", buf);
}


pid = translate_pid(pid, source, target);
if (pid < 0)
err(2, "translate");

printf("%d\n", pid);
return 0;
}
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