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SubjectRe: [PATCH v6] pidns: introduce syscall translate_pid
Hi,

On Mon, Jul 16, 2018 at 10:57:48AM -0700, Nagarathnam Muthusamy wrote:
> On 06/01/2018 12:18 PM, Konstantin Khlebnikov wrote:
> > Each process have different pids, one for each pid namespace it belongs.
> > When interaction happens within single pid-ns translation isn't required.
> > More complicated scenarios needs special handling.
> >
> > For example:
> > - reading pid-files or logs written inside container with pid namespace
> > - writing logs with internal pids outside container for pushing them into
> > - attaching with ptrace to tasks from different pid namespace
> >
> > Generally speaking, any cross pid-ns API with pids needs translation.
> >
> > Currently there are several interfaces that could be used here:
> >
> > Pid namespaces are identified by device and inode of /proc/[pid]/ns/pid.
> >
> > Pids for nested pid namespaces are shown in file /proc/[pid]/status.
> > In some cases pid translation could be easily done using this information.
> > Backward translation requires scanning all tasks and becomes really
> > complicated for deeper namespace nesting.
> >
> > Unix socket automatically translates pid attached to SCM_CREDENTIALS.
> > This requires CAP_SYS_ADMIN for sending arbitrary pids and entering
> > into pid namespace, this expose process and could be insecure.
> >
> > This patch adds new syscall for converting pids between pid namespaces:
> >
> > pid_t translate_pid(pid_t pid, int source, int target);
> >
> > Pid-namespaces are referred file descriptors opened to proc files
> > /proc/[pid]/ns/pid or /proc/[pid]/ns/pid_for_children.
> > Negative argument points to current pid namespace.
> >
> > Syscall returns pid in target pid-ns or zero if task have no pid there.
> >
> > Error codes:
> > EBADF - file descriptor is closed
> > EINVAL - file descriptor isn't pid namespace
> > ESRCH - task not found in @source namespace
> >
> > Translation could breach pid-ns isolation and return pids from outer pid
> > namespaces iff process already has file descriptor for these namespaces.
> >
> > 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?
> >
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> > Reanimated-by: Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>
> >
> > ---
> >
> > 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: https://lkml.org/lkml/2017/10/13/177
> > * rename from getvpid() 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
> > v5: https://lkml.org/lkml/2018/4/4/677
> > * rewrite commit message
> > * resolve pidns by task pid or by pidns fd
> > * add arguments source_type and target_type
> > v6:
> > * revert back minimized v4 design
> > * rebase to next-20180601
> > * fix COND_SYSCALL stub
> > * use next syscall number, old used for io_pgetevents
> >
> > --- sample tool ---
> >
> > #define _GNU_SOURCE
> > #include <sys/syscall.h>
> > #include <sys/types.h>
> > #include <fcntl.h>
> > #include <unistd.h>
> > #include <stdlib.h>
> > #include <stdio.h>
> > #include <err.h>
> >
> > #ifndef SYS_translate_pid
> > #ifdef __x86_64__
> > #define SYS_translate_pid 334
> > #elif defined __i386__
> > #define SYS_translate_pid 386
> > #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> <target>", argv[0]);
> >
> > pid = atoi(argv[1]);
> > source = atoi(argv[2]);
> > target = atoi(argv[3]);
> >
> > if (source > 0) {
> > snprintf(buf, sizeof(buf), "/proc/%d/ns/pid", source);
> > source = open(buf, O_RDONLY);
> > if (source < 0)
> > err(2, "open source %s", buf);
> > }
> >
> > if (target > 0) {
> > snprintf(buf, sizeof(buf), "/proc/%d/ns/pid", target);
> > target = open(buf, O_RDONLY);
> > if (target < 0)
> > err(2, "open target %s", buf);
> > }
> >
> > pid = translate_pid(pid, source, target);
> > if (pid < 0)
> > err(2, "translate_pid");
> >
> > printf("%d\n", pid);
> > return 0;
> > }
> >
> > ---
> > ---
> > 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 14a2f996e543..e70685750d43 100644
> > --- a/arch/x86/entry/syscalls/syscall_32.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_32.tbl
> > @@ -397,3 +397,4 @@
> > 383 i386 statx sys_statx __ia32_sys_statx
> > 384 i386 arch_prctl sys_arch_prctl __ia32_compat_sys_arch_prctl
> > 385 i386 io_pgetevents sys_io_pgetevents __ia32_compat_sys_io_pgetevents
> > +386 i386 translate_pid sys_translate_pid __ia32_sys_translate_pid
> > diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
> > index cd36232ab62f..ebfd89055424 100644
> > --- a/arch/x86/entry/syscalls/syscall_64.tbl
> > +++ b/arch/x86/entry/syscalls/syscall_64.tbl
> > @@ -342,6 +342,7 @@
> > 331 common pkey_free __x64_sys_pkey_free
> > 332 common statx __x64_sys_statx
> > 333 common io_pgetevents __x64_sys_io_pgetevents
> > +334 common translate_pid __x64_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 390e814fdc8d..3f33971cf1c8 100644
> > --- a/include/linux/syscalls.h
> > +++ b/include/linux/syscalls.h
> > @@ -843,6 +843,7 @@ asmlinkage long sys_clock_adjtime(clockid_t which_clock,
> > struct timex __user *tx);
> > asmlinkage long sys_syncfs(int fd);
> > asmlinkage long sys_setns(int fd, int nstype);
> > +asmlinkage long sys_translate_pid(pid_t pid, int source, int target);
> > asmlinkage long sys_sendmmsg(int fd, struct mmsghdr __user *msg,
> > unsigned int vlen, unsigned flags);
> > asmlinkage long sys_process_vm_readv(pid_t pid,
> > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
> > index 2a2ac53d8b8b..3b872cbbe264 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>
> > @@ -380,6 +381,71 @@ 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 06b4ccee0047..bf276e9ace9a 100644
> > --- a/kernel/sys_ni.c
> > +++ b/kernel/sys_ni.c
> > @@ -153,6 +153,9 @@ COND_SYSCALL_COMPAT(kexec_load);
> > COND_SYSCALL(init_module);
> > COND_SYSCALL(delete_module);
> >
> > +/* kernel/pid_namespace.c */
> > +COND_SYSCALL(translate_pid);
> > +
> > /* kernel/posix-timers.c */
> >
> > /* kernel/printk.c */
> >
>
> Ping :-) Checking back again for Ack or comments.

JFYI, I'll try to attract more attention to this proposal
by mentioning it in my talk at the LPC 2018 as a potential solution
for one of several problems we have in strace, see
https://www.linuxplumbersconf.org/event/2/contributions/78/


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