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Date: Mon, 14 Apr 2008 09:58:40 -0500
From: "Serge E. Hallyn" <serue@...ibm.com>
To: Manfred Spraul <manfred@...orfullife.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"Serge E. Hallyn" <serue@...ibm.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Pavel Emelyanov <xemul@...nvz.org>,
Sukadev Bhattiprolu <sukadev@...ibm.com>,
Pierre PEIFFER <pierre.peiffer@...l.net>
Subject: Re: [PATCH 1/2] fix sys_unshare()+SEM_UNDO: add support for
CLONE_SYSVSEM
Quoting Manfred Spraul (manfred@...orfullife.com):
> Andrew Morton wrote:
>> On Sun, 13 Apr 2008 10:04:17 +0200 Manfred Spraul
>> <manfred@...orfullife.com> wrote:
>>
>>
>>> 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)
>>>
>>>
>>
>> Is this a non-back-compatible change?
>>
>>
> It adds a new feature - previously sys_unshare(CLONE_SYSVSEM) returned
> -EINVAL.
>
>>> Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
>>> ---
>>> ipc/sem.c | 1 +
>>> kernel/fork.c | 18 ++++++++++++++----
>>> 2 files changed, 15 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/ipc/sem.c b/ipc/sem.c
>>> index 0b45a4d..35841bd 100644
>>> --- a/ipc/sem.c
>>> +++ b/ipc/sem.c
>>> @@ -1298,6 +1298,7 @@ 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;
>>> diff --git a/kernel/fork.c b/kernel/fork.c
>>> index 9c042f9..7f242b0 100644
>>> --- a/kernel/fork.c
>>> +++ b/kernel/fork.c
>>> @@ -1675,13 +1675,17 @@ static int unshare_fd(unsigned long
>>> unshare_flags, struct files_struct **new_fdp
>>> }
>>> /*
>>> - * Unsharing of semundo for tasks created with CLONE_SYSVSEM is not
>>> - * supported yet
>>> + * Unsharing of semundo for tasks created with CLONE_SYSVSEM doesn't
>>> require
>>> + * any allocations: it means that the task leaves the existing undo
>>> lists,
>>> + * just like sys_exit(). The new undo lists are allocated on demand in
>>> the
>>> + * ipc syscalls.
>>> + * new_ulistp is set to a non-NULL value, the caller expects that on
>>> success.
>>> */
>>> static int unshare_semundo(unsigned long unshare_flags, struct
>>> sem_undo_list **new_ulistp)
>>> {
>>> - if (unshare_flags & CLONE_SYSVSEM)
>>> - return -EINVAL;
>>> + if (unshare_flags & CLONE_SYSVSEM) {
>>> + *new_ulistp = (void*)1;
>>> + }
>>>
>>
>> And can we do anything nicer than this?
>>
>>
> Attached is an alternative. If you prefer it, I'll send another patch set.
FWIW I definately far far prefer this version :)
As for 'maintainers', in the end wrt this code I'd defer to any two of
Pavel, Nadia, and Pierre, each of who I've seen do a great deal of
digging around this code.
(I think I saw some set of these go into -mm so I guess I'll just grab
mmotm and test with that a bit later today)
thanks,
-serge
> --
> Manfred
> diff --git a/ipc/sem.c b/ipc/sem.c
> index 0b45a4d..35841bd 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1298,6 +1298,7 @@ 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;
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 9c042f9..535aa92 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1675,18 +1675,6 @@ static int unshare_fd(unsigned long unshare_flags, struct files_struct **new_fdp
> }
>
> /*
> - * 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_*
> * functions used by do_fork() cannot be used here directly
> @@ -1701,7 +1689,6 @@ 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;
>
> check_unshare_flags(&unshare_flags);
> @@ -1724,13 +1711,17 @@ 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 || (unshare_flags & CLONE_SYSVSEM) || new_nsproxy) {
> + if (unshare_flags & CLONE_SYSVSEM) {
> + /*
> + * CLONE_SYSVSEM is equivalent to sys_exit().
> + */
> + exit_sem(current);
> + }
>
> if (new_nsproxy) {
> switch_task_namespaces(current, new_nsproxy);
> @@ -1766,7 +1757,6 @@ 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);
--
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