[Devel] [PATCH] namespaces: introduce sys_hijack (v4)
Paul Menage
menage at google.com
Tue Oct 16 02:09:44 PDT 2007
One thought on this - could we make the API have a "which" parameter
that indicates the type of thing being acted upon? E.g., like
sys_setpriority(), which can specify the target as a process, a pgrp
or a user.
Right now the target would just be a process, but I'd really like the
ability to be able to specify an fd on a cgroup directory to indicate
that I want the child to inherit from that cgroup's namespaces. That
way you wouldn't need to keep a child process alive in the namespace
just to act as a hijack target.
Paul
On 10/9/07, Serge E. Hallyn <serue at us.ibm.com> wrote:
> >From 945fe66259cd0cfdc2fe846287b7821e329a558c Mon Sep 17 00:00:00 2001
> From: sergeh at us.ibm.com <hallyn at kernel.(none)>
> Date: Tue, 9 Oct 2007 08:30:30 -0700
> Subject: [PATCH] namespaces: introduce sys_hijack (v4)
>
> Move most of do_fork() into a new do_fork_task() which acts on
> a new argument, task, rather than on current. do_fork() becomes
> a call to do_fork_task(current, ...).
>
> Introduce sys_hijack (for x86 only so far). It is like clone, but
> in place of a stack pointer (which is assumed null) it accepts a
> pid. The process identified by that pid is the one which is
> actually cloned. Some state - include the file table, the signals
> and sighand (and hence tty), and the ->parent are taken from the
> calling process.
>
> The effect is a sort of namespace enter. The following program
> uses sys_hijack to 'enter' all namespaces of the specified pid.
> For instance in one terminal, do
>
> mount -t cgroup -ons /cgroup
> hostname
> qemu
> ns_exec -u /bin/sh
> hostname serge
> echo $$
> 1073
> cat /proc/$$/cgroup
> ns:/node_1073
>
> In another terminal then do
>
> hostname
> qemu
> cat /proc/$$/cgroup
> ns:/
> hijack 1073
> hostname
> serge
> cat /proc/$$/cgroup
> ns:/node_1073
>
> sys_hijack is arch-dependent and is only implemented for i386 so far.
>
> Changelog:
> Aug 23: send a stop signal to the hijacked process
> (like ptrace does).
> Oct 09: Update for 2.6.23-rc8-mm2 (mainly pidns)
> Don't take task_lock under rcu_read_lock
> Send hijacked process to cgroup_fork() as
> the first argument.
> Removed some unneeded task_locks.
>
> ==============================================================
> hijack.c
> ==============================================================
>
> int do_clone_task(void)
> {
> execl("/bin/sh", "/bin/sh", NULL);
> }
>
> int main(int argc, char *argv[])
> {
> int pid;
> int ret;
> int status;
>
> if (argc < 2)
> return 1;
> pid = atoi(argv[1]);
>
> ret = syscall(327, SIGCHLD, pid, NULL, NULL);
>
> if (ret == 0) {
> return do_clone_task();
> } else if (ret < 0) {
> perror("sys_hijack");
> } else {
> printf("waiting on cloned process %d\n", ret);
> while (waitpid(ret, &status, __WCLONE) != ret);
> printf("cloned process %d exited with %d\n", ret, status);
> }
>
> return ret;
> }
> ==============================================================
>
> Signed-off-by: Serge Hallyn <serue at us.ibm.com>
> ---
> arch/i386/kernel/process.c | 58 ++++++++++++++++++++++++++++++-
> arch/i386/kernel/syscall_table.S | 1 +
> arch/s390/kernel/process.c | 12 +++++-
> include/asm-i386/unistd.h | 3 +-
> include/linux/cgroup.h | 5 ++-
> include/linux/pid.h | 2 +-
> include/linux/ptrace.h | 1 +
> include/linux/sched.h | 2 +
> include/linux/syscalls.h | 1 +
> kernel/cgroup.c | 8 ++--
> kernel/fork.c | 69 +++++++++++++++++++++++++++----------
> kernel/pid.c | 5 ++-
> kernel/ptrace.c | 7 ++++
> 13 files changed, 141 insertions(+), 33 deletions(-)
>
> diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
> index bfcd01e..01f4d16 100644
> --- a/arch/i386/kernel/process.c
> +++ b/arch/i386/kernel/process.c
> @@ -455,8 +455,15 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
> unsigned long unused,
> struct task_struct * p, struct pt_regs * regs)
> {
> + return copy_a_thread(current, nr, clone_flags, esp, unused,
> + p, regs);
> +}
> +
> +int copy_a_thread(struct task_struct *tsk, int nr, unsigned long clone_flags,
> + unsigned long esp, unsigned long unused,
> + struct task_struct * p, struct pt_regs * regs)
> +{
> struct pt_regs * childregs;
> - struct task_struct *tsk;
> int err;
>
> childregs = task_pt_regs(p);
> @@ -471,7 +478,6 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
>
> savesegment(gs,p->thread.gs);
>
> - tsk = current;
> if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
> p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
> IO_BITMAP_BYTES, GFP_KERNEL);
> @@ -783,6 +789,54 @@ asmlinkage int sys_clone(struct pt_regs regs)
> return do_fork(clone_flags, newsp, ®s, 0, parent_tidptr, child_tidptr);
> }
>
> +asmlinkage int sys_hijack(struct pt_regs regs)
> +{
> + unsigned long clone_flags;
> + int __user *parent_tidptr, *child_tidptr;
> + pid_t pid;
> + struct task_struct *task;
> + int ret = -EINVAL;
> +
> + clone_flags = regs.ebx;
> + pid = regs.ecx;
> + parent_tidptr = (int __user *)regs.edx;
> + child_tidptr = (int __user *)regs.edi;
> +
> + rcu_read_lock();
> + task = find_task_by_vpid(pid);
> + if (task)
> + get_task_struct(task);
> + rcu_read_unlock();
> +
> + if (task) {
> + task_lock(task);
> + put_task_struct(task);
> + }
> +
> + if (task) {
> + if (!ptrace_may_attach_locked(task)) {
> + ret = -EPERM;
> + goto out_put_task;
> + }
> + if (task->ptrace) {
> + ret = -EBUSY;
> + goto out_put_task;
> + }
> + force_sig_specific(SIGSTOP, task);
> +
> + task_unlock(task);
> + ret = do_fork_task(task, clone_flags, regs.esp, ®s, 0,
> + parent_tidptr, child_tidptr);
> + wake_up_process(task);
> + task = NULL;
> + }
> +
> +out_put_task:
> + if (task)
> + task_unlock(task);
> + return ret;
> +}
> +
> /*
> * This is trivial, and on the face of it looks like it
> * could equally well be done in user mode.
> diff --git a/arch/i386/kernel/syscall_table.S b/arch/i386/kernel/syscall_table.S
> index df6e41e..495930c 100644
> --- a/arch/i386/kernel/syscall_table.S
> +++ b/arch/i386/kernel/syscall_table.S
> @@ -326,3 +326,4 @@ ENTRY(sys_call_table)
> .long sys_fallocate
> .long sys_revokeat /* 325 */
> .long sys_frevoke
> + .long sys_hijack
> diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
> index 70c5737..f256e7a 100644
> --- a/arch/s390/kernel/process.c
> +++ b/arch/s390/kernel/process.c
> @@ -223,6 +223,14 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long new_stackp,
> unsigned long unused,
> struct task_struct * p, struct pt_regs * regs)
> {
> + return copy_a_thread(current, nr, clone_flags, new_stackp, unused,
> + p, regs);
> +}
> +
> +int copy_a_thread(struct task_struct *task, int nr, unsigned long clone_flags,
> + unsigned long new_stackp, unsigned long unused,
> + struct task_struct * p, struct pt_regs * regs)
> +{
> struct fake_frame
> {
> struct stack_frame sf;
> @@ -251,8 +259,8 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long new_stackp,
> * save fprs to current->thread.fp_regs to merge them with
> * the emulated registers and then copy the result to the child.
> */
> - save_fp_regs(¤t->thread.fp_regs);
> - memcpy(&p->thread.fp_regs, ¤t->thread.fp_regs,
> + save_fp_regs(&task->thread.fp_regs);
> + memcpy(&p->thread.fp_regs, &task->thread.fp_regs,
> sizeof(s390_fp_regs));
> p->thread.user_seg = __pa((unsigned long) p->mm->pgd) | _SEGMENT_TABLE;
> /* Set a new TLS ? */
> diff --git a/include/asm-i386/unistd.h b/include/asm-i386/unistd.h
> index 006c1b3..fe6eeb4 100644
> --- a/include/asm-i386/unistd.h
> +++ b/include/asm-i386/unistd.h
> @@ -332,10 +332,11 @@
> #define __NR_fallocate 324
> #define __NR_revokeat 325
> #define __NR_frevoke 326
> +#define __NR_hijack 327
>
> #ifdef __KERNEL__
>
> -#define NR_syscalls 327
> +#define NR_syscalls 328
>
> #define __ARCH_WANT_IPC_PARSE_VERSION
> #define __ARCH_WANT_OLD_READDIR
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index 8747932..cb6d335 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -26,7 +26,7 @@ extern int cgroup_init(void);
> extern void cgroup_init_smp(void);
> extern void cgroup_lock(void);
> extern void cgroup_unlock(void);
> -extern void cgroup_fork(struct task_struct *p);
> +extern void cgroup_fork(struct task_struct *parent, struct task_struct *p);
> extern void cgroup_fork_callbacks(struct task_struct *p);
> extern void cgroup_post_fork(struct task_struct *p);
> extern void cgroup_exit(struct task_struct *p, int run_callbacks);
> @@ -309,7 +309,8 @@ void cgroup_iter_end(struct cgroup *cont, struct cgroup_iter *it);
> static inline int cgroup_init_early(void) { return 0; }
> static inline int cgroup_init(void) { return 0; }
> static inline void cgroup_init_smp(void) {}
> -static inline void cgroup_fork(struct task_struct *p) {}
> +static inline void cgroup_fork(struct task_struct *parent,
> + struct task_struct *p) {}
> static inline void cgroup_fork_callbacks(struct task_struct *p) {}
> static inline void cgroup_post_fork(struct task_struct *p) {}
> static inline void cgroup_exit(struct task_struct *p, int callbacks) {}
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index e29a900..145dce7 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -119,7 +119,7 @@ extern struct pid *find_pid(int nr);
> extern struct pid *find_get_pid(int nr);
> extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
>
> -extern struct pid *alloc_pid(struct pid_namespace *ns);
> +extern struct pid *alloc_pid(struct task_struct *task);
> extern void FASTCALL(free_pid(struct pid *pid));
> extern void zap_pid_ns_processes(struct pid_namespace *pid_ns);
>
> diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
> index ae8146a..727a4a9 100644
> --- a/include/linux/ptrace.h
> +++ b/include/linux/ptrace.h
> @@ -97,6 +97,7 @@ extern void __ptrace_link(struct task_struct *child,
> extern void __ptrace_unlink(struct task_struct *child);
> extern void ptrace_untrace(struct task_struct *child);
> extern int ptrace_may_attach(struct task_struct *task);
> +extern int ptrace_may_attach_locked(struct task_struct *task);
>
> static inline void ptrace_link(struct task_struct *child,
> struct task_struct *new_parent)
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 4f21af1..d85c3cf 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1630,6 +1630,7 @@ extern struct mm_struct *get_task_mm(struct task_struct *task);
> extern void mm_release(struct task_struct *, struct mm_struct *);
>
> extern int copy_thread(int, unsigned long, unsigned long, unsigned long, struct task_struct *, struct pt_regs *);
> +extern int copy_a_thread(struct task_struct *, int, unsigned long, unsigned long, unsigned long, struct task_struct *, struct pt_regs *);
> extern void flush_thread(void);
> extern void exit_thread(void);
>
> @@ -1645,6 +1646,7 @@ extern int allow_signal(int);
> extern int disallow_signal(int);
>
> extern int do_execve(char *, char __user * __user *, char __user * __user *, struct pt_regs *);
> +extern long do_fork_task(struct task_struct *task, unsigned long, unsigned long, struct pt_regs *, unsigned long, int __user *, int __user *);
> extern long do_fork(unsigned long, unsigned long, struct pt_regs *, unsigned long, int __user *, int __user *);
> struct task_struct *fork_idle(int);
>
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index f696874..5bc7384 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -616,5 +616,6 @@ int kernel_execve(const char *filename, char *const argv[], char *const envp[]);
>
> asmlinkage long sys_revokeat(int dfd, const char __user *filename);
> asmlinkage long sys_frevoke(unsigned int fd);
> +asmlinkage long sys_hijack(unsigned long flags, pid_t pid, int __user *ptid, int __user *ctid);
>
> #endif
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 1e8aa53..e587896 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2460,12 +2460,12 @@ static struct file_operations proc_cgroupstats_operations = {
> * At the point that cgroup_fork() is called, 'current' is the parent
> * task, and the passed argument 'child' points to the child task.
> */
> -void cgroup_fork(struct task_struct *child)
> +void cgroup_fork(struct task_struct *parent, struct task_struct *child)
> {
> - task_lock(current);
> - child->cgroups = current->cgroups;
> + task_lock(parent);
> + child->cgroups = parent->cgroups;
> get_css_set(child->cgroups);
> - task_unlock(current);
> + task_unlock(parent);
> INIT_LIST_HEAD(&child->cg_list);
> }
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index f85731a..ac73f3e 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -621,13 +621,14 @@ struct fs_struct *copy_fs_struct(struct fs_struct *old)
>
> EXPORT_SYMBOL_GPL(copy_fs_struct);
>
> -static inline int copy_fs(unsigned long clone_flags, struct task_struct * tsk)
> +static inline int copy_fs(unsigned long clone_flags,
> + struct task_struct * src, struct task_struct * tsk)
> {
> if (clone_flags & CLONE_FS) {
> - atomic_inc(¤t->fs->count);
> + atomic_inc(&src->fs->count);
> return 0;
> }
> - tsk->fs = __copy_fs_struct(current->fs);
> + tsk->fs = __copy_fs_struct(src->fs);
> if (!tsk->fs)
> return -ENOMEM;
> return 0;
> @@ -973,7 +974,8 @@ static inline void rt_mutex_init_task(struct task_struct *p)
> * parts of the process environment (as per the clone
> * flags). The actual kick-off is left to the caller.
> */
> -static struct task_struct *copy_process(unsigned long clone_flags,
> +static struct task_struct *copy_process(struct task_struct *task,
> + unsigned long clone_flags,
> unsigned long stack_start,
> struct pt_regs *regs,
> unsigned long stack_size,
> @@ -1007,15 +1009,17 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> goto fork_out;
>
> retval = -ENOMEM;
> - p = dup_task_struct(current);
> + p = dup_task_struct(task);
> if (!p)
> goto fork_out;
>
> rt_mutex_init_task(p);
>
> #ifdef CONFIG_TRACE_IRQFLAGS
> - DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
> - DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
> + if (task == current) {
> + DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
> + DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
> + }
> #endif
> retval = -EAGAIN;
> if (atomic_read(&p->user->processes) >=
> @@ -1084,7 +1088,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> #endif
> p->io_context = NULL;
> p->audit_context = NULL;
> - cgroup_fork(p);
> + cgroup_fork(task, p);
> #ifdef CONFIG_NUMA
> p->mempolicy = mpol_copy(p->mempolicy);
> if (IS_ERR(p->mempolicy)) {
> @@ -1132,7 +1136,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> goto bad_fork_cleanup_audit;
> if ((retval = copy_files(clone_flags, p)))
> goto bad_fork_cleanup_semundo;
> - if ((retval = copy_fs(clone_flags, p)))
> + if ((retval = copy_fs(clone_flags, task, p)))
> goto bad_fork_cleanup_files;
> if ((retval = copy_sighand(clone_flags, p)))
> goto bad_fork_cleanup_fs;
> @@ -1144,13 +1148,13 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> goto bad_fork_cleanup_mm;
> if ((retval = copy_namespaces(clone_flags, p)))
> goto bad_fork_cleanup_keys;
> - retval = copy_thread(0, clone_flags, stack_start, stack_size, p, regs);
> + retval = copy_a_thread(task, 0, clone_flags, stack_start, stack_size, p, regs);
> if (retval)
> goto bad_fork_cleanup_namespaces;
>
> if (pid != &init_struct_pid) {
> retval = -ENOMEM;
> - pid = alloc_pid(task_active_pid_ns(p));
> + pid = alloc_pid(task);
> if (!pid)
> goto bad_fork_cleanup_namespaces;
>
> @@ -1164,7 +1168,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
> p->pid = pid_nr(pid);
> p->tgid = p->pid;
> if (clone_flags & CLONE_THREAD)
> - p->tgid = current->tgid;
> + p->tgid = task->tgid;
>
> p->set_child_tid = (clone_flags & CLONE_CHILD_SETTID) ? child_tidptr : NULL;
> /*
> @@ -1380,7 +1384,7 @@ struct task_struct * __cpuinit fork_idle(int cpu)
> struct task_struct *task;
> struct pt_regs regs;
>
> - task = copy_process(CLONE_VM, 0, idle_regs(®s), 0, NULL,
> + task = copy_process(current, CLONE_VM, 0, idle_regs(®s), 0, NULL,
> &init_struct_pid);
> if (!IS_ERR(task))
> init_idle(task, cpu);
> @@ -1405,12 +1409,12 @@ static inline int fork_traceflag (unsigned clone_flags)
> }
>
> /*
> - * Ok, this is the main fork-routine.
> - *
> - * It copies the process, and if successful kick-starts
> - * it and waits for it to finish using the VM if required.
> + * if called with task!=current, then caller must ensure that
> + * 1. it has a reference to task
> + * 2. current must have ptrace permission to task
> */
> -long do_fork(unsigned long clone_flags,
> +long do_fork_task(struct task_struct *task,
> + unsigned long clone_flags,
> unsigned long stack_start,
> struct pt_regs *regs,
> unsigned long stack_size,
> @@ -1421,13 +1425,23 @@ long do_fork(unsigned long clone_flags,
> int trace = 0;
> long nr;
>
> + if (task != current) {
> + /* sanity checks */
> + /* we only want to allow hijacking the simplest cases */
> + if (clone_flags & CLONE_SYSVSEM)
> + return -EINVAL;
> + if (current->ptrace)
> + return -EPERM;
> + if (task->ptrace)
> + return -EINVAL;
> + }
> if (unlikely(current->ptrace)) {
> trace = fork_traceflag (clone_flags);
> if (trace)
> clone_flags |= CLONE_PTRACE;
> }
>
> - p = copy_process(clone_flags, stack_start, regs, stack_size,
> + p = copy_process(task, clone_flags, stack_start, regs, stack_size,
> child_tidptr, NULL);
> /*
> * Do this prior waking up the new thread - the thread pointer
> @@ -1489,6 +1503,23 @@ long do_fork(unsigned long clone_flags,
> return nr;
> }
>
> +/*
> + * Ok, this is the main fork-routine.
> + *
> + * It copies the process, and if successful kick-starts
> + * it and waits for it to finish using the VM if required.
> + */
> +long do_fork(unsigned long clone_flags,
> + unsigned long stack_start,
> + struct pt_regs *regs,
> + unsigned long stack_size,
> + int __user *parent_tidptr,
> + int __user *child_tidptr)
> +{
> + return do_fork_task(current, clone_flags, stack_start,
> + regs, stack_size, parent_tidptr, child_tidptr);
> +}
> +
> #ifndef ARCH_MIN_MMSTRUCT_ALIGN
> #define ARCH_MIN_MMSTRUCT_ALIGN 0
> #endif
> diff --git a/kernel/pid.c b/kernel/pid.c
> index d7388d7..b887a6a 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -238,14 +238,15 @@ fastcall void free_pid(struct pid *pid)
> call_rcu(&pid->rcu, delayed_put_pid);
> }
>
> -struct pid *alloc_pid(struct pid_namespace *ns)
> +struct pid *alloc_pid(struct task_struct *srctsk)
> {
> struct pid *pid;
> enum pid_type type;
> int i, nr;
> - struct pid_namespace *tmp;
> + struct pid_namespace *tmp, *ns;
> struct upid *upid;
>
> + ns = task_active_pid_ns(srctsk);
> pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL);
> if (!pid)
> goto out;
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 7c76f2f..c65c9fe 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -159,6 +159,13 @@ int ptrace_may_attach(struct task_struct *task)
> return !err;
> }
>
> +int ptrace_may_attach_locked(struct task_struct *task)
> +{
> + int err;
> + err = may_attach(task);
> + return !err;
> +}
> +
> int ptrace_attach(struct task_struct *task)
> {
> int retval;
> --
> 1.5.1
>
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