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Commit 9bfb23fc authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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sys_unshare: remove the dead CLONE_THREAD/SIGHAND/VM code 



Cleanup: kill the dead code which does nothing but complicates the code
and confuses the reader.

sys_unshare(CLONE_THREAD/SIGHAND/VM) is not really implemented, and I
doubt very much it will ever work.  At least, nobody even tried since the
original 99d1419d ("unshare system call -v5: system call
handler function") was applied more than 4 years ago.

And the code is not consistent.  unshare_thread() always fails
unconditionally, while unshare_sighand() and unshare_vm() pretend to work
if there is nothing to unshare.

Remove unshare_thread(), unshare_sighand(), unshare_vm() helpers and
related variables and add a simple CLONE_THREAD | CLONE_SIGHAND| CLONE_VM
check into check_unshare_flags().

Also, move the "CLONE_NEWNS needs CLONE_FS" check from
check_unshare_flags() to sys_unshare().  This looks more consistent and
matches the similar do_sysvsem check in sys_unshare().

Note: with or without this patch "atomic_read(mm->mm_users) > 1" can give
a false positive due to get_task_mm().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarRoland McGrath <roland@redhat.com>
Cc: Janak Desai <janak@us.ibm.com>
Cc: Daniel Lezcano <daniel.lezcano@free.fr>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: default avatarSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4d51985e

kernel/fork.c

+25 −98
Original line number Diff line number Diff line
@@ -1519,38 +1519,24 @@ void __init proc_caches_init(void) 
}



/*

 * Check constraints on flags passed to the unshare system call and

 * force unsharing of additional process context as appropriate.

 * Check constraints on flags passed to the unshare system call.

 */

static void check_unshare_flags(unsigned long *flags_ptr)

static int check_unshare_flags(unsigned long unshare_flags)

{

	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|

				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|

				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))

		return -EINVAL;

	/*

	 * If unsharing a thread from a thread group, must also

	 * unshare vm.

	 */

	if (*flags_ptr & CLONE_THREAD)

		*flags_ptr |= CLONE_VM;



	/*

	 * If unsharing vm, must also unshare signal handlers.

	 */

	if (*flags_ptr & CLONE_VM)

		*flags_ptr |= CLONE_SIGHAND;



	/*

	 * If unsharing namespace, must also unshare filesystem information.

	 */

	if (*flags_ptr & CLONE_NEWNS)

		*flags_ptr |= CLONE_FS;

}



/*

 * Unsharing of tasks created with CLONE_THREAD is not supported yet

	 * Not implemented, but pretend it works if there is nothing to

	 * unshare. Note that unsharing CLONE_THREAD or CLONE_SIGHAND

	 * needs to unshare vm.

	 */

static int unshare_thread(unsigned long unshare_flags)

{

	if (unshare_flags & CLONE_THREAD)

	if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) {

		/* FIXME: get_task_mm() increments ->mm_users */

		if (atomic_read(&current->mm->mm_users) > 1)

			return -EINVAL;

	}



	return 0;

}
@@ -1576,34 +1562,6 @@ static int unshare_fs(unsigned long unshare_flags, struct fs_struct **new_fsp) 
	return 0;

}



/*

 * Unsharing of sighand is not supported yet

 */

static int unshare_sighand(unsigned long unshare_flags, struct sighand_struct **new_sighp)

{

	struct sighand_struct *sigh = current->sighand;



	if ((unshare_flags & CLONE_SIGHAND) && atomic_read(&sigh->count) > 1)

		return -EINVAL;

	else

		return 0;

}



/*

 * Unshare vm if it is being shared

 */

static int unshare_vm(unsigned long unshare_flags, struct mm_struct **new_mmp)

{

	struct mm_struct *mm = current->mm;



	if ((unshare_flags & CLONE_VM) &&

	    (mm && atomic_read(&mm->mm_users) > 1)) {

		return -EINVAL;

	}



	return 0;

}



/*

 * Unshare file descriptor table if it is being shared

 */
@@ -1632,23 +1590,21 @@ static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp 
 */

SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)

{

	int err = 0;

	struct fs_struct *fs, *new_fs = NULL;

	struct sighand_struct *new_sigh = NULL;

	struct mm_struct *mm, *new_mm = NULL, *active_mm = NULL;

	struct files_struct *fd, *new_fd = NULL;

	struct nsproxy *new_nsproxy = NULL;

	int do_sysvsem = 0;

	int err;



	check_unshare_flags(&unshare_flags);



	/* Return -EINVAL for all unsupported flags */

	err = -EINVAL;

	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|

				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|

				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWNET))

	err = check_unshare_flags(unshare_flags);

	if (err)

		goto bad_unshare_out;



	/*

	 * If unsharing namespace, must also unshare filesystem information.

	 */

	if (unshare_flags & CLONE_NEWNS)

		unshare_flags |= CLONE_FS;

	/*

	 * CLONE_NEWIPC must also detach from the undolist: after switching

	 * to a new ipc namespace, the semaphore arrays from the old
@@ -1656,21 +1612,15 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) 
	 */

	if (unshare_flags & (CLONE_NEWIPC|CLONE_SYSVSEM))

		do_sysvsem = 1;

	if ((err = unshare_thread(unshare_flags)))

		goto bad_unshare_out;

	if ((err = unshare_fs(unshare_flags, &new_fs)))

		goto bad_unshare_cleanup_thread;

	if ((err = unshare_sighand(unshare_flags, &new_sigh)))

		goto bad_unshare_cleanup_fs;

	if ((err = unshare_vm(unshare_flags, &new_mm)))

		goto bad_unshare_cleanup_sigh;

		goto bad_unshare_out;

	if ((err = unshare_fd(unshare_flags, &new_fd)))

		goto bad_unshare_cleanup_vm;

		goto bad_unshare_cleanup_fs;

	if ((err = unshare_nsproxy_namespaces(unshare_flags, &new_nsproxy,

			new_fs)))

		goto bad_unshare_cleanup_fd;



	if (new_fs ||  new_mm || new_fd || do_sysvsem || new_nsproxy) {

	if (new_fs || new_fd || do_sysvsem || new_nsproxy) {

		if (do_sysvsem) {

			/*

			 * CLONE_SYSVSEM is equivalent to sys_exit().
@@ -1696,19 +1646,6 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) 
			spin_unlock(&fs->lock);

		}



		if (new_mm) {

			mm = current->mm;

			active_mm = current->active_mm;

			current->mm = new_mm;

			current->active_mm = new_mm;

			if (current->signal->oom_score_adj == OOM_SCORE_ADJ_MIN) {

				atomic_dec(&mm->oom_disable_count);

				atomic_inc(&new_mm->oom_disable_count);

			}

			activate_mm(active_mm, new_mm);

			new_mm = mm;

		}



		if (new_fd) {

			fd = current->files;

			current->files = new_fd;
@@ -1725,20 +1662,10 @@ bad_unshare_cleanup_fd: 
	if (new_fd)

		put_files_struct(new_fd);



bad_unshare_cleanup_vm:

	if (new_mm)

		mmput(new_mm);



bad_unshare_cleanup_sigh:

	if (new_sigh)

		if (atomic_dec_and_test(&new_sigh->count))

			kmem_cache_free(sighand_cachep, new_sigh);



bad_unshare_cleanup_fs:

	if (new_fs)

		free_fs_struct(new_fs);



bad_unshare_cleanup_thread:

bad_unshare_out:

	return err;

}