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Commit 9edff4ab authored by Manfred Spraul's avatar Manfred Spraul Committed by Linus Torvalds
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ipc: sysvsem: implement sys_unshare(CLONE_SYSVSEM) 



sys_unshare(CLONE_NEWIPC) doesn't handle the undo lists properly, this can
cause a kernel memory corruption.  CLONE_NEWIPC must detach from the existing
undo lists.

Fix, part 1: add support for sys_unshare(CLONE_SYSVSEM)

The original reason to not support it was the potential (inevitable?)
confusion due to the fact that sys_unshare(CLONE_SYSVSEM) has the
inverse meaning of clone(CLONE_SYSVSEM).

Our two most reasonable options then appear to be (1) fully support
CLONE_SYSVSEM, or (2) continue to refuse explicit CLONE_SYSVSEM,
but always do it anyway on unshare(CLONE_SYSVSEM).  This patch does
(1).

Changelog:
	Apr 16: SEH: switch to Manfred's alternative patch which
		removes the unshare_semundo() function which
		always refused CLONE_SYSVSEM.

Signed-off-by: default avatarManfred Spraul <manfred@colorfullife.com>
Signed-off-by: default avatarSerge E. Hallyn <serue@us.ibm.com>
Acked-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 44f564a4

ipc/sem.c

+1 −0
Original line number Diff line number Diff line
@@ -1250,6 +1250,7 @@ void exit_sem(struct task_struct *tsk) 
	undo_list = tsk->sysvsem.undo_list;

	if (!undo_list)

		return;

	tsk->sysvsem.undo_list = NULL;



	if (!atomic_dec_and_test(&undo_list->refcnt))

		return;

kernel/fork.c

+11 −18
Original line number Diff line number Diff line
@@ -1668,18 +1668,6 @@ static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp 
	return 0;

}



/*

 * Unsharing of semundo for tasks created with CLONE_SYSVSEM is not

 * supported yet

 */

static int unshare_semundo(unsigned long unshare_flags, struct sem_undo_list **new_ulistp)

{

	if (unshare_flags & CLONE_SYSVSEM)

		return -EINVAL;



	return 0;

}



/*

 * unshare allows a process to 'unshare' part of the process

 * context which was originally shared using clone.  copy_*
@@ -1695,8 +1683,8 @@ asmlinkage long sys_unshare(unsigned long unshare_flags) 
	struct sighand_struct *new_sigh = NULL;

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

	struct files_struct *fd, *new_fd = NULL;

	struct sem_undo_list *new_ulist = NULL;

	struct nsproxy *new_nsproxy = NULL;

	int do_sysvsem = 0;



	check_unshare_flags(&unshare_flags);
@@ -1708,6 +1696,8 @@ asmlinkage long sys_unshare(unsigned long unshare_flags) 
				CLONE_NEWNET))

		goto bad_unshare_out;



	if (unshare_flags & CLONE_SYSVSEM)

		do_sysvsem = 1;

	if ((err = unshare_thread(unshare_flags)))

		goto bad_unshare_out;

	if ((err = unshare_fs(unshare_flags, &new_fs)))
@@ -1718,13 +1708,17 @@ asmlinkage long sys_unshare(unsigned long unshare_flags) 
		goto bad_unshare_cleanup_sigh;

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

		goto bad_unshare_cleanup_vm;

	if ((err = unshare_semundo(unshare_flags, &new_ulist)))

		goto bad_unshare_cleanup_fd;

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

			new_fs)))

		goto bad_unshare_cleanup_semundo;

		goto bad_unshare_cleanup_fd;



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

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

		if (do_sysvsem) {

			/*

			 * CLONE_SYSVSEM is equivalent to sys_exit().

			 */

			exit_sem(current);

		}



		if (new_nsproxy) {

			switch_task_namespaces(current, new_nsproxy);
@@ -1760,7 +1754,6 @@ asmlinkage long sys_unshare(unsigned long unshare_flags) 
	if (new_nsproxy)

		put_nsproxy(new_nsproxy);



bad_unshare_cleanup_semundo:

bad_unshare_cleanup_fd:

	if (new_fd)

		put_files_struct(new_fd);