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vfork: make it killable

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Make vfork() killable.

Change do_fork(CLONE_VFORK) to do wait_for_completion_killable().  If it
fails we do not return to the user-mode and never touch the memory shared
with our child.

However, in this case we should clear child->vfork_done before return, we
use task_lock() in do_fork()->wait_for_vfork_done() and
complete_vfork_done() to serialize with each other.

Note: now that we use task_lock() we don't really need completion, we
could turn task->vfork_done into "task_struct *wake_up_me" but this needs
some complications.

NOTE: this and the next patches do not affect in-kernel users of
CLONE_VFORK, kernel threads run with all signals ignored including
SIGKILL/SIGSTOP.

However this is obviously the user-visible change.  Not only a fatal
signal can kill the vforking parent, a sub-thread can do execve or
exit_group() and kill the thread sleeping in vfork().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2012-03-05 14:59:13 -08:00 committed by Linus Torvalds
parent c415c3b47e
commit d68b46fe16
2 changed files with 33 additions and 9 deletions
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2
include/linux/sched.h
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@ -2372,7 +2372,7 @@ static inline int thread_group_empty(struct task_struct *p)
* Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring * Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
* subscriptions and synchronises with wait4(). Also used in procfs. Also * subscriptions and synchronises with wait4(). Also used in procfs. Also
* pins the final release of task.io_context. Also protects ->cpuset and * pins the final release of task.io_context. Also protects ->cpuset and
* ->cgroup.subsys[]. * ->cgroup.subsys[]. And ->vfork_done.
* *
* Nests both inside and outside of read_lock(&tasklist_lock). * Nests both inside and outside of read_lock(&tasklist_lock).
* It must not be nested with write_lock_irq(&tasklist_lock), * It must not be nested with write_lock_irq(&tasklist_lock),

40
kernel/fork.c
View File

@ -670,10 +670,34 @@ struct mm_struct *mm_access(struct task_struct *task, unsigned int mode)
void complete_vfork_done(struct task_struct *tsk) void complete_vfork_done(struct task_struct *tsk)
{ {
struct completion *vfork_done = tsk->vfork_done; struct completion *vfork;
tsk->vfork_done = NULL; task_lock(tsk);
complete(vfork_done); vfork = tsk->vfork_done;
if (likely(vfork)) {
tsk->vfork_done = NULL;
complete(vfork);
}
task_unlock(tsk);
}
static int wait_for_vfork_done(struct task_struct *child,
struct completion *vfork)
{
int killed;
freezer_do_not_count();
killed = wait_for_completion_killable(vfork);
freezer_count();
if (killed) {
task_lock(child);
child->vfork_done = NULL;
task_unlock(child);
}
put_task_struct(child);
return killed;
} }
/* Please note the differences between mmput and mm_release. /* Please note the differences between mmput and mm_release.
@ -717,7 +741,8 @@ void mm_release(struct task_struct *tsk, struct mm_struct *mm)
* If we're exiting normally, clear a user-space tid field if * If we're exiting normally, clear a user-space tid field if
* requested. We leave this alone when dying by signal, to leave * requested. We leave this alone when dying by signal, to leave
* the value intact in a core dump, and to save the unnecessary * the value intact in a core dump, and to save the unnecessary
* trouble otherwise. Userland only wants this done for a sys_exit. * trouble, say, a killed vfork parent shouldn't touch this mm.
* Userland only wants this done for a sys_exit.
*/ */
if (tsk->clear_child_tid) { if (tsk->clear_child_tid) {
if (!(tsk->flags & PF_SIGNALED) && if (!(tsk->flags & PF_SIGNALED) &&
@ -1551,6 +1576,7 @@ long do_fork(unsigned long clone_flags,
if (clone_flags & CLONE_VFORK) { if (clone_flags & CLONE_VFORK) {
p->vfork_done = &vfork; p->vfork_done = &vfork;
init_completion(&vfork); init_completion(&vfork);
get_task_struct(p);
} }
/* /*
@ -1568,10 +1594,8 @@ long do_fork(unsigned long clone_flags,
ptrace_event(trace, nr); ptrace_event(trace, nr);
if (clone_flags & CLONE_VFORK) { if (clone_flags & CLONE_VFORK) {
freezer_do_not_count(); if (!wait_for_vfork_done(p, &vfork))
wait_for_completion(&vfork); ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
freezer_count();
ptrace_event(PTRACE_EVENT_VFORK_DONE, nr);
} }
} else { } else {
nr = PTR_ERR(p); nr = PTR_ERR(p);