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ipc: sysvsem: implement sys_unshare(CLONE_SYSVSEM)

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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: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Acked-by: "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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Manfred Spraul 2008-04-29 01:00:57 -07:00 committed by Linus Torvalds
parent 44f564a4bf
commit 9edff4ab1f
2 changed files with 12 additions and 18 deletions
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1
ipc/sem.c
View File

@ -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;

29
kernel/fork.c
View File

@ -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);