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SubjectRe: [PATCH -mm 7/7] forbid the use of the unshare syscall on ipc namespaces
This patch looks as an overkill for me.

If you really care about things you describe, you can forbid unsharing in cases:

1.
undo_list = tsk->sysvsem.undo_list;
if (undo_list)
REFUSE_UNSHARE;
2. vma exists with vma->vm_ops == &shm_vm_ops;
3. file opened with f_op == &shm_file_operations

I also dislike exec() operation for such sort of things since you can have no executable
at hands due to changed fs namespace.

Thanks,
Kirill


> This patch forbids the use of the unshare() syscall on ipc namespaces.
>
> The purpose of this restriction is to protect the system from
> inconsistencies when the namespace is unshared. e.g. shared memory ids
> will be removed but not the memory mappings, semaphore ids will be
> removed but the semundos not cleared.
>
>
> Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
> Cc: Andrew Morton <akpm@osdl.org>
> Cc: Pavel Emelianov <xemul@openvz.org>
> Cc: Kirill Korotaev <dev@openvz.org>
> Cc: Andrey Savochkin <saw@sw.ru>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Herbert Poetzl <herbert@13thfloor.at>
> Cc: Sam Vilain <sam.vilain@catalyst.net.nz>
> Cc: Serge E. Hallyn <serue@us.ibm.com>
> Cc: Dave Hansen <haveblue@us.ibm.com>
>
> ---
> kernel/fork.c | 23 +++++------------------
> 1 file changed, 5 insertions(+), 18 deletions(-)
>
> Index: 2.6.18-rc1-mm1/kernel/fork.c
> ===================================================================
> --- 2.6.18-rc1-mm1.orig/kernel/fork.c
> +++ 2.6.18-rc1-mm1/kernel/fork.c
> @@ -1604,7 +1604,6 @@ asmlinkage long sys_unshare(unsigned lon
> struct sem_undo_list *new_ulist = NULL;
> struct nsproxy *new_nsproxy = NULL, *old_nsproxy = NULL;
> struct uts_namespace *uts, *new_uts = NULL;
> - struct ipc_namespace *ipc, *new_ipc = NULL;
>
> check_unshare_flags(&unshare_flags);
>
> @@ -1612,12 +1611,12 @@ asmlinkage long sys_unshare(unsigned lon
> err = -EINVAL;
> if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
> CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
> - CLONE_NEWUTS|CLONE_NEWIPC))
> + CLONE_NEWUTS))
> goto bad_unshare_out;
>
> /* Also return -EINVAL for all unsharable namespaces. May be a
> * -EACCES would be more appropriate ? */
> - if (unshare_flags & CLONE_NEWUSER)
> + if (unshare_flags & (CLONE_NEWUSER|CLONE_NEWIPC))
> goto bad_unshare_out;
>
> if ((err = unshare_thread(unshare_flags)))
> @@ -1636,20 +1635,18 @@ asmlinkage long sys_unshare(unsigned lon
> goto bad_unshare_cleanup_fd;
> if ((err = unshare_utsname(unshare_flags, &new_uts)))
> goto bad_unshare_cleanup_semundo;
> - if ((err = unshare_ipcs(unshare_flags, &new_ipc)))
> - goto bad_unshare_cleanup_uts;
>
> - if (new_ns || new_uts || new_ipc) {
> + if (new_ns || new_uts) {
> old_nsproxy = current->nsproxy;
> new_nsproxy = dup_namespaces(old_nsproxy);
> if (!new_nsproxy) {
> err = -ENOMEM;
> - goto bad_unshare_cleanup_ipc;
> + goto bad_unshare_cleanup_uts;
> }
> }
>
> if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist ||
> - new_uts || new_ipc) {
> + new_uts) {
>
> task_lock(current);
>
> @@ -1697,22 +1694,12 @@ asmlinkage long sys_unshare(unsigned lon
> new_uts = uts;
> }
>
> - if (new_ipc) {
> - ipc = current->nsproxy->ipc_ns;
> - current->nsproxy->ipc_ns = new_ipc;
> - new_ipc = ipc;
> - }
> -
> task_unlock(current);
> }
>
> if (new_nsproxy)
> put_nsproxy(new_nsproxy);
>
> -bad_unshare_cleanup_ipc:
> - if (new_ipc)
> - put_ipc_ns(new_ipc);
> -
> bad_unshare_cleanup_uts:
> if (new_uts)
> put_uts_ns(new_uts);
>
> --
>

-
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