[kernel-hardening] Re: [PATCH v2] shm: handle separate PID namespaces case

Vasiliy Kulikov
2011-07-15T06:45:42Z

Hi Andrew,

On Tue, Jul 05, 2011 at 21:37 +0400, Vasiliy Kulikov wrote:
> shm_try_destroy_orphaned() and shm_try_destroy_current() didn't handle
> the case of separate PID namespaces, but a single IPC namespace. If
> there are tasks with the same PID values using the same shmem object,
> the wrong destroy decision could be reached.
>
> On shm segment creation store the pointer to the creator task in
> shmid_kernel->shm_creator field and zero it on task exit. Then
> use the ->shm_creator insread of shm_cprid in both functions. As
> shmid_kernel object is already locked at this stage, no additional
> locking is needed.

Can you please pick these 2 patches? This one is a bug fix and another
is a cleanup/speedup. Thanks!

> Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
> ---
> include/linux/shm.h | 3 +++
> ipc/shm.c | 27 ++++++++++++++++++++-------
> 2 files changed, 23 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/shm.h b/include/linux/shm.h
> index b030a4e..12d2234 100644
> --- a/include/linux/shm.h
> +++ b/include/linux/shm.h
> @@ -95,6 +95,9 @@ struct shmid_kernel /* private to the kernel */
> pid_t shm_cprid;
> pid_t shm_lprid;
> struct user_struct *mlock_user;
> +
> + /* The task created the shm object. NULL if the task is dead. */
> + struct task_struct *shm_creator;
> };
>
> /* shm_mode upper byte flags */
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 22006f1..3baae98 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -239,7 +239,23 @@ static int shm_try_destroy_current(int id, void *p, void *data)
> if (IS_ERR(shp))
> return 0;
>
> - if (shp->shm_cprid != task_tgid_vnr(current)) {
> + if (shp->shm_creator != current) {
> + shm_unlock(shp);
> + return 0;
> + }
> +
> + /*
> + * Mark it as orphaned to destroy the segment when
> + * kernel.shm_rmid_forced is changed.
> + * It is noop if the following shm_may_destroy() returns true.
> + */
> + shp->shm_creator = NULL;
> +
> + /*
> + * Don't even try to destroy it. If shm_rmid_forced=0 and IPC_RMID
> + * is not set, it shouldn't be deleted here.
> + */
> + if (!ns->shm_rmid_forced) {
> shm_unlock(shp);
> return 0;
> }
> @@ -255,7 +271,6 @@ static int shm_try_destroy_orphaned(int id, void *p, void *data)
> {
> struct ipc_namespace *ns = data;
> struct shmid_kernel *shp = shm_lock(ns, id);
> - struct task_struct *task;
>
> if (IS_ERR(shp))
> return 0;
> @@ -263,11 +278,8 @@ static int shm_try_destroy_orphaned(int id, void *p, void *data)
> /*
> * We want to destroy segments without users and with already
> * exit'ed originating process.
> - *
> - * XXX: the originating process may exist in another pid namespace.
> */
> - task = find_task_by_vpid(shp->shm_cprid);
> - if (task != NULL) {
> + if (shp->shm_creator != NULL) {
> shm_unlock(shp);
> return 0;
> }
> @@ -295,7 +307,7 @@ void exit_shm(struct task_struct *task)
> if (!nsp)
> return;
> ns = nsp->ipc_ns;
> - if (!ns || !ns->shm_rmid_forced)
> + if (!ns)
> return;
>
> /* Destroy all already created segments, but not mapped yet */
> @@ -494,6 +506,7 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params)
> shp->shm_segsz = size;
> shp->shm_nattch = 0;
> shp->shm_file = file;
> + shp->shm_creator = current;
> /*
> * shmid gets reported as "inode#" in /proc/pid/maps.
> * proc-ps tools use this. Changing this will break them.
> --
> 1.7.0.4

--
Vasiliy Kulikov
http://www.openwall.com - bringing security into open computing environments