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raw_syscalls: add lxc_raw_clone{_cb}()

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Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
This commit is contained in:
Christian Brauner 2018-09-30 19:47:58 +02:00
parent 13be27338c
commit 38e5c2dbba
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GPG Key ID: 8EB056D53EECB12D
8 changed files with 128 additions and 118 deletions
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1
src/lxc/attach.c
View File

@ -59,6 +59,7 @@
#include "macro.h"
#include "mainloop.h"
#include "namespace.h"
#include "raw_syscalls.h"
#include "terminal.h"
#include "utils.h"

74
src/lxc/namespace.c
View File

@ -75,80 +75,6 @@ pid_t lxc_clone(int (*fn)(void *), void *arg, int flags)
return ret;
}
/**
* This is based on raw_clone in systemd but adapted to our needs. This uses
* copy on write semantics and doesn't pass a stack. CLONE_VM is tricky and
* doesn't really matter to us so disallow it.
*
* The nice thing about this is that we get fork() behavior. That is
* lxc_raw_clone() returns 0 in the child and the child pid in the parent.
*/
pid_t lxc_raw_clone(unsigned long flags)
{
/* These flags don't interest at all so we don't jump through any hoopes
* of retrieving them and passing them to the kernel.
*/
errno = EINVAL;
if ((flags & (CLONE_VM | CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
CLONE_CHILD_CLEARTID | CLONE_SETTLS)))
return -EINVAL;
#if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
/* On s390/s390x and cris the order of the first and second arguments
* of the system call is reversed.
*/
return (int)syscall(__NR_clone, NULL, flags | SIGCHLD);
#elif defined(__sparc__) && defined(__arch64__)
{
/**
* sparc64 always returns the other process id in %o0, and
* a boolean flag whether this is the child or the parent in
* %o1. Inline assembly is needed to get the flag returned
* in %o1.
*/
int in_child;
int child_pid;
asm volatile("mov %2, %%g1\n\t"
"mov %3, %%o0\n\t"
"mov 0 , %%o1\n\t"
"t 0x6d\n\t"
"mov %%o1, %0\n\t"
"mov %%o0, %1"
: "=r"(in_child), "=r"(child_pid)
: "i"(__NR_clone), "r"(flags | SIGCHLD)
: "%o1", "%o0", "%g1");
if (in_child)
return 0;
else
return child_pid;
}
#elif defined(__ia64__)
/* On ia64 the stack and stack size are passed as separate arguments. */
return (int)syscall(__NR_clone, flags | SIGCHLD, NULL, 0);
#else
return (int)syscall(__NR_clone, flags | SIGCHLD, NULL);
#endif
}
pid_t lxc_raw_clone_cb(int (*fn)(void *), void *args, unsigned long flags)
{
pid_t pid;
pid = lxc_raw_clone(flags);
if (pid < 0)
return -1;
/* exit() is not thread-safe and might mess with the parent's signal
* handlers and other stuff when exec() fails.
*/
if (pid == 0)
_exit(fn(args));
return pid;
}
/* Leave the user namespace at the first position in the array of structs so
* that we always attach to it first when iterating over the struct and using
* setns() to switch namespaces. This especially affects lxc_attach(): Suppose

44
src/lxc/namespace.h
View File

@ -128,55 +128,13 @@ int clone(int (*fn)(void *), void *child_stack,
* corresponding libc wrapper. glibc currently does not run pthread_atfork()
* handlers but does not guarantee that they are not. Other libcs might or
* might not run pthread_atfork() handlers. If you require guarantees please
* refer to the lxc_raw_clone*() functions below.
* refer to the lxc_raw_clone*() functions in raw_syscalls.{c,h}.
*
* - should call lxc_raw_getpid():
* The child should use lxc_raw_getpid() to retrieve its pid.
*/
extern pid_t lxc_clone(int (*fn)(void *), void *arg, int flags);
/**
* lxc_raw_clone() - create a new process
*
* - fork() behavior:
* This function returns 0 in the child and > 0 in the parent.
*
* - copy-on-write:
* This function does not allocate a new stack and relies on copy-on-write
* semantics.
*
* - supports subset of ClONE_* flags:
* lxc_raw_clone() intentionally only supports a subset of the flags available
* to the actual system call. Please refer to the implementation what flags
* cannot be used. Also, please don't assume that just because a flag isn't
* explicitly checked for as being unsupported that it is supported. If in
* doubt or not sufficiently familiar with process creation in the kernel and
* interactions with libcs this function should be used.
*
* - no pthread_atfork() handlers:
* This function circumvents - as much as this this is possible - any libc
* wrappers and thus does not run any pthread_atfork() handlers. Make sure
* that this is safe to do in the context you are trying to call this
* function.
*
* - must call lxc_raw_getpid():
* The child must use lxc_raw_getpid() to retrieve its pid.
*/
extern pid_t lxc_raw_clone(unsigned long flags);
/**
* lxc_raw_clone_cb() - create a new process
*
* - non-fork() behavior:
* Function does return pid of the child or -1 on error. Pass in a callback
* function via the "fn" argument that gets executed in the child process. The
* "args" argument is passed to "fn".
*
* All other comments that apply to lxc_raw_clone() apply to lxc_raw_clone_cb()
* as well.
*/
extern pid_t lxc_raw_clone_cb(int (*fn)(void *), void *args,
unsigned long flags);
extern int lxc_namespace_2_cloneflag(const char *namespace);
extern int lxc_namespace_2_ns_idx(const char *namespace);
extern int lxc_namespace_2_std_identifiers(char *namespaces);

79
src/lxc/raw_syscalls.c
View File

@ -2,12 +2,16 @@
#define _GNU_SOURCE 1
#endif
#include <errno.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/syscall.h>
#include <unistd.h>
#include "config.h"
#include "macro.h"
#include "raw_syscalls.h"
int lxc_raw_execveat(int dirfd, const char *pathname, char *const argv[],
char *const envp[], int flags)
@ -19,3 +23,78 @@ int lxc_raw_execveat(int dirfd, const char *pathname, char *const argv[],
return -1;
#endif
}
/*
* This is based on raw_clone in systemd but adapted to our needs. This uses
* copy on write semantics and doesn't pass a stack. CLONE_VM is tricky and
* doesn't really matter to us so disallow it.
*
* The nice thing about this is that we get fork() behavior. That is
* lxc_raw_clone() returns 0 in the child and the child pid in the parent.
*/
pid_t lxc_raw_clone(unsigned long flags)
{
/*
* These flags don't interest at all so we don't jump through any hoopes
* of retrieving them and passing them to the kernel.
*/
errno = EINVAL;
if ((flags & (CLONE_VM | CLONE_PARENT_SETTID | CLONE_CHILD_SETTID |
CLONE_CHILD_CLEARTID | CLONE_SETTLS)))
return -EINVAL;
#if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
/* On s390/s390x and cris the order of the first and second arguments
* of the system call is reversed.
*/
return (int)syscall(__NR_clone, NULL, flags | SIGCHLD);
#elif defined(__sparc__) && defined(__arch64__)
{
/*
* sparc64 always returns the other process id in %o0, and a
* boolean flag whether this is the child or the parent in %o1.
* Inline assembly is needed to get the flag returned in %o1.
*/
int in_child;
int child_pid;
asm volatile("mov %2, %%g1\n\t"
"mov %3, %%o0\n\t"
"mov 0 , %%o1\n\t"
"t 0x6d\n\t"
"mov %%o1, %0\n\t"
"mov %%o0, %1"
: "=r"(in_child), "=r"(child_pid)
: "i"(__NR_clone), "r"(flags | SIGCHLD)
: "%o1", "%o0", "%g1");
if (in_child)
return 0;
else
return child_pid;
}
#elif defined(__ia64__)
/* On ia64 the stack and stack size are passed as separate arguments. */
return (int)syscall(__NR_clone, flags | SIGCHLD, NULL, prctl_arg(0));
#else
return (int)syscall(__NR_clone, flags | SIGCHLD, NULL);
#endif
}
pid_t lxc_raw_clone_cb(int (*fn)(void *), void *args, unsigned long flags)
{
pid_t pid;
pid = lxc_raw_clone(flags);
if (pid < 0)
return -1;
/*
* exit() is not thread-safe and might mess with the parent's signal
* handlers and other stuff when exec() fails.
*/
if (pid == 0)
_exit(fn(args));
return pid;
}

44
src/lxc/raw_syscalls.h
View File

@ -23,8 +23,52 @@
#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/syscall.h>
/*
* lxc_raw_clone() - create a new process
*
* - fork() behavior:
* This function returns 0 in the child and > 0 in the parent.
*
* - copy-on-write:
* This function does not allocate a new stack and relies on copy-on-write
* semantics.
*
* - supports subset of ClONE_* flags:
* lxc_raw_clone() intentionally only supports a subset of the flags available
* to the actual system call. Please refer to the implementation what flags
* cannot be used. Also, please don't assume that just because a flag isn't
* explicitly checked for as being unsupported that it is supported. If in
* doubt or not sufficiently familiar with process creation in the kernel and
* interactions with libcs this function should be used.
*
* - no pthread_atfork() handlers:
* This function circumvents - as much as this this is possible - any libc
* wrappers and thus does not run any pthread_atfork() handlers. Make sure
* that this is safe to do in the context you are trying to call this
* function.
*
* - must call lxc_raw_getpid():
* The child must use lxc_raw_getpid() to retrieve its pid.
*/
extern pid_t lxc_raw_clone(unsigned long flags);
/*
* lxc_raw_clone_cb() - create a new process
*
* - non-fork() behavior:
* Function does return pid of the child or -1 on error. Pass in a callback
* function via the "fn" argument that gets executed in the child process.
* The "args" argument is passed to "fn".
*
* All other comments that apply to lxc_raw_clone() apply to lxc_raw_clone_cb()
* as well.
*/
extern pid_t lxc_raw_clone_cb(int (*fn)(void *), void *args, unsigned long flags);
extern int lxc_raw_execveat(int dirfd, const char *pathname, char *const argv[],
char *const envp[], int flags);

1
src/lxc/start.c
View File

@ -70,6 +70,7 @@
#include "monitor.h"
#include "namespace.h"
#include "network.h"
#include "raw_syscalls.h"
#include "start.h"
#include "storage/storage.h"
#include "storage/storage_utils.h"

1
src/lxc/utils.c
View File

@ -51,6 +51,7 @@
#include "lxclock.h"
#include "namespace.h"
#include "parse.h"
#include "raw_syscalls.h"
#include "syscall_wrappers.h"
#include "utils.h"

2
src/tests/lxc_raw_clone.c
View File

@ -38,7 +38,7 @@
#include <sys/types.h>
#include "lxctest.h"
#include "namespace.h"
#include "raw_syscalls.h"
#include "utils.h"
int main(int argc, char *argv[])