Re: + shm-extend-forced-shm-destroy-to-support-objects-from-several-ipc-nses.patch added to -mm tree

Hi Andrew,

On 10/28/21 00:51, akpm@linux-foundation.org wrote:

The patch titled Subject: shm: extend forced shm destroy to support objects from several IPC nses has been added to the -mm tree. Its filename is shm-extend-forced-shm-destroy-to-support-objects-from-several-ipc-nses.patch

Could you replace the patch with the attached version?

See https://lore.kernel.org/all/8ba678da-207e-ea00-a56d-736a2184e69e@colorfullif... for details

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/shm-extend-forced-shm-destroy-to-s... and later at https://ozlabs.org/~akpm/mmotm/broken-out/shm-extend-forced-shm-destroy-to-s...

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

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---

From: Alexander Mikhalitsyn alexander.mikhalitsyn@virtuozzo.com Subject: shm: extend forced shm destroy to support objects from several IPC nses

Currently, exit_shm function not designed to work properly when task->sysvshm.shm_clist holds shm objects from different IPC namespaces.

This is a real pain when sysctl kernel.shm_rmid_forced = 1, because it leads to use-after-free (reproducer exists).

That particular patch is attempt to fix the problem by extending exit_shm mechanism to handle shm's destroy from several IPC ns'es.

To achieve that we do several things:

1. add namespace (non-refcounted) pointer to the struct shmid_kernel

2. during new shm object creation (newseg()/shmget syscall) we initialize this pointer by current task IPC ns

3. exit_shm() fully reworked such that it traverses over all shp's in task->sysvshm.shm_clist and gets IPC namespace not from current task as it was before but from shp's object itself, then call shm_destroy(shp, ns).

Note. We need to be really careful here, because as it was said before (1), our pointer to IPC ns non-refcnt'ed. To be on the safe side we using special helper get_ipc_ns_not_zero() which allows to get IPC ns refcounter only if IPC ns not in the "state of destruction".

Q/A

Q: Why we can access shp->ns memory using non-refcounted pointer? A: Because shp object lifetime is always shorther than IPC namespace lifetime, so, if we get shp object from the task->sysvshm.shm_clist while holding task_lock(task) nobody can steal our namespace.

Q: Does this patch change semantics of unshare/setns/clone syscalls? A: Not. It's just fixes non-covered case when process may leave IPC namespace without getting task->sysvshm.shm_clist list cleaned up.

Link: https://lkml.kernel.org/r/20211027224348.611025-3-alexander.mikhalitsyn@virt... Fixes: ab602f79915 ("shm: make exit_shm work proportional to task activity") Co-developed-by: Manfred Spraul manfred@colorfullife.com Signed-off-by: Manfred Spraul manfred@colorfullife.com Signed-off-by: Alexander Mikhalitsyn alexander.mikhalitsyn@virtuozzo.com Cc: "Eric W. Biederman" ebiederm@xmission.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: Greg KH gregkh@linuxfoundation.org Cc: Andrei Vagin avagin@gmail.com Cc: Pavel Tikhomirov ptikhomirov@virtuozzo.com Cc: Vasily Averin vvs@virtuozzo.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org

---

include/linux/ipc_namespace.h | 15 ++ include/linux/sched/task.h | 2 include/linux/shm.h | 2 ipc/shm.c | 170 +++++++++++++++++++++++--------- 4 files changed, 142 insertions(+), 47 deletions(-)

--- a/include/linux/ipc_namespace.h~shm-extend-forced-shm-destroy-to-support-objects-from-several-ipc-nses +++ a/include/linux/ipc_namespace.h @@ -131,6 +131,16 @@ static inline struct ipc_namespace *get_ return ns; } +static inline struct ipc_namespace *get_ipc_ns_not_zero(struct ipc_namespace *ns) +{

• if (ns) {

• if (refcount_inc_not_zero(&ns->ns.count))
  

• 	return ns;
  

• }
• return NULL;

+}

• extern void put_ipc_ns(struct ipc_namespace *ns); #else static inline struct ipc_namespace *copy_ipcs(unsigned long flags,

@@ -146,6 +156,11 @@ static inline struct ipc_namespace *get_ { return ns; }

+static inline struct ipc_namespace *get_ipc_ns_not_zero(struct ipc_namespace *ns) +{

• return ns;

+} static inline void put_ipc_ns(struct ipc_namespace *ns) { --- a/include/linux/sched/task.h~shm-extend-forced-shm-destroy-to-support-objects-from-several-ipc-nses +++ a/include/linux/sched/task.h @@ -157,7 +157,7 @@ static inline struct vm_struct *task_sta

• Protects ->fs, ->files, ->mm, ->group_info, ->comm, keyring
• subscriptions and synchronises with wait4(). Also used in procfs. Also
• pins the final release of task.io_context. Also protects ->cpuset and

• • ->cgroup.subsys[]. And ->vfork_done.

• • ->cgroup.subsys[]. And ->vfork_done. And ->sysvshm.shm_clist.
  • Nests both inside and outside of read_lock(&tasklist_lock).
  • It must not be nested with write_lock_irq(&tasklist_lock),

--- a/include/linux/shm.h~shm-extend-forced-shm-destroy-to-support-objects-from-several-ipc-nses +++ a/include/linux/shm.h @@ -11,7 +11,7 @@ struct file; #ifdef CONFIG_SYSVIPC struct sysv_shm {

• struct list_head shm_clist;

• struct list_head shm_clist; };

long do_shmat(int shmid, char __user *shmaddr, int shmflg, unsigned long *addr, --- a/ipc/shm.c~shm-extend-forced-shm-destroy-to-support-objects-from-several-ipc-nses +++ a/ipc/shm.c @@ -62,9 +62,18 @@ struct shmid_kernel /* private to the ke struct pid *shm_lprid; struct ucounts *mlock_ucounts;

• /* The task created the shm object. NULL if the task is dead. */

• /*

• * The task created the shm object, for looking up
  

• * task->sysvshm.shm_clist_lock
  

• */
  

  struct task_struct *shm_creator;

• struct list_head shm_clist; /* list by creator */

• /*

• * list by creator. shm_clist_lock required for read/write
  

• * if list_empty(), then the creator is dead already
  

• */
  

• struct list_head shm_clist;
• struct ipc_namespace *ns; } __randomize_layout;

/* shm_mode upper byte flags */ @@ -115,6 +124,7 @@ static void do_shm_rmid(struct ipc_names struct shmid_kernel *shp; shp = container_of(ipcp, struct shmid_kernel, shm_perm);

• WARN_ON(ns != shp->ns);

if (shp->shm_nattch) { shp->shm_perm.mode |= SHM_DEST; @@ -225,10 +235,36 @@ static void shm_rcu_free(struct rcu_head kfree(shp); } -static inline void shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *s) +/*

• • It has to be called with shp locked.
• • It must be called before ipc_rmid()
• */

+static inline void shm_clist_rm(struct shmid_kernel *shp) {

• list_del(&s->shm_clist);
• ipc_rmid(&shm_ids(ns), &s->shm_perm);

• struct task_struct *creator;
• /*

• * A concurrent exit_shm may do a list_del_init() as well.
  

• * Just do nothing if exit_shm already did the work
  

• */
  

• if (list_empty(&shp->shm_clist))

• return;
  

• /*

• * shp->shm_creator is guaranteed to be valid *only*
  

• * if shp->shm_clist is not empty.
  

• */
  

• creator = shp->shm_creator;
• task_lock(creator);
• list_del_init(&shp->shm_clist);
• task_unlock(creator);

+}

+static inline void shm_rmid(struct shmid_kernel *s) +{

• shm_clist_rm(s);
• ipc_rmid(&shm_ids(s->ns), &s->shm_perm); }

@@ -283,7 +319,7 @@ static void shm_destroy(struct ipc_names shm_file = shp->shm_file; shp->shm_file = NULL; ns->shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;

• shm_rmid(ns, shp);

• shm_rmid(shp); shm_unlock(shp); if (!is_file_hugepages(shm_file)) shmem_lock(shm_file, 0, shp->mlock_ucounts);

@@ -306,10 +342,10 @@ static void shm_destroy(struct ipc_names

• 2. sysctl kernel.shm_rmid_forced is set to 1.

*/ -static bool shm_may_destroy(struct ipc_namespace *ns, struct shmid_kernel *shp) +static bool shm_may_destroy(struct shmid_kernel *shp) { return (shp->shm_nattch == 0) &&

•       (ns->shm_rmid_forced ||
  

•       (shp->ns->shm_rmid_forced ||
  

  (shp->shm_perm.mode & SHM_DEST)); }

@@ -340,7 +376,7 @@ static void shm_close(struct vm_area_str ipc_update_pid(&shp->shm_lprid, task_tgid(current)); shp->shm_dtim = ktime_get_real_seconds(); shp->shm_nattch--;

• if (shm_may_destroy(ns, shp))

• if (shm_may_destroy(shp)) shm_destroy(ns, shp); else shm_unlock(shp);

@@ -361,10 +397,10 @@ static int shm_try_destroy_orphaned(int * * As shp->* are changed under rwsem, it's safe to skip shp locking. */

• if (shp->shm_creator != NULL)

• if (!list_empty(&shp->shm_clist)) return 0;

• if (shm_may_destroy(ns, shp)) {

• if (shm_may_destroy(shp)) { shm_lock_by_ptr(shp); shm_destroy(ns, shp); }

@@ -382,48 +418,87 @@ void shm_destroy_orphaned(struct ipc_nam /* Locking assumes this will only be called with task == current */ void exit_shm(struct task_struct *task) {

• struct ipc_namespace *ns = task->nsproxy->ipc_ns;
• struct shmid_kernel *shp, *n;

• for (;;) {

• struct shmid_kernel *shp;
  

• struct ipc_namespace *ns;
  

• if (list_empty(&task->sysvshm.shm_clist))

• return;
  

• task_lock(task);
  

• if (list_empty(&task->sysvshm.shm_clist)) {
  

• 	task_unlock(task);
  

• 	break;
  

• }
  

• shp = list_first_entry(&task->sysvshm.shm_clist, struct shmid_kernel,
  

• 		shm_clist);
  

• /* 1) unlink */
  

• list_del_init(&shp->shm_clist);
  

• /*

• * If kernel.shm_rmid_forced is not set then only keep track of
  

• * which shmids are orphaned, so that a later set of the sysctl
  

• * can clean them up.
  

• */
  

• if (!ns->shm_rmid_forced) {

• down_read(&shm_ids(ns).rwsem);
  

• list_for_each_entry(shp, &task->sysvshm.shm_clist, shm_clist)
  

• 	shp->shm_creator = NULL;
  

  /*

•  * Only under read lock but we are only called on current
  

•  * so no entry on the list will be shared.
  

•  * 2) Get pointer to the ipc namespace. It is worth to say
  

•  * that this pointer is guaranteed to be valid because
  

•  * shp lifetime is always shorter than namespace lifetime
  

•  * in which shp lives.
  

•  * We taken task_lock it means that shp won't be freed.
  

  */

• list_del(&task->sysvshm.shm_clist);
  

• up_read(&shm_ids(ns).rwsem);
  

• return;
  

• }

• ns = shp->ns;
  

• /*

• * Destroy all already created segments, that were not yet mapped,
  

• * and mark any mapped as orphan to cover the sysctl toggling.
  

• * Destroy is skipped if shm_may_destroy() returns false.
  

• */
  

• down_write(&shm_ids(ns).rwsem);
• list_for_each_entry_safe(shp, n, &task->sysvshm.shm_clist, shm_clist) {

• shp->shm_creator = NULL;
  

• /*
  

•  * 3) If kernel.shm_rmid_forced is not set then only keep track of
  

•  * which shmids are orphaned, so that a later set of the sysctl
  

•  * can clean them up.
  

•  */
  

• if (!ns->shm_rmid_forced) {
  

• 	task_unlock(task);
  

• 	continue;
  

• }
  

• if (shm_may_destroy(ns, shp)) {
  

• /*
  

•  * 4) get a reference to the namespace.
  

•  *    The refcount could be already 0. If it is 0, then
  

•  *    the shm objects will be free by free_ipc_work().
  

•  */
  

• ns = get_ipc_ns_not_zero(ns);
  

• if (ns) {
  

• 	/*
  

• 	 * 5) get a reference to the shp itself.
  

• 	 *   This cannot fail: shm_clist_rm() is called before
  

• 	 *   ipc_rmid(), thus the refcount cannot be 0.
  

• 	 */
  

• 	WARN_ON(!ipc_rcu_getref(&shp->shm_perm));
  

• }
  

• task_unlock(task);
  

• if (ns) {
  

• 	down_write(&shm_ids(ns).rwsem);
  shm_lock_by_ptr(shp);
  

• 	shm_destroy(ns, shp);
  

• 	/*
  

• 	 * rcu_read_lock was implicitly taken in
  

• 	 * shm_lock_by_ptr, it's safe to call
  

• 	 * ipc_rcu_putref here
  

• 	 */
  

• 	ipc_rcu_putref(&shp->shm_perm, shm_rcu_free);
  

• 	if (ipc_valid_object(&shp->shm_perm)) {
  

• 		if (shm_may_destroy(shp))
  

• 			shm_destroy(ns, shp);
  

• 		else
  

• 			shm_unlock(shp);
  

• 	} else {
  

• 		/*
  

• 		 * Someone else deleted the shp from namespace
  

• 		 * idr/kht while we have waited.
  

• 		 * Just unlock and continue.
  

• 		 */
  

• 		shm_unlock(shp);
  

• 	}
  

• 	up_write(&shm_ids(ns).rwsem);
  

• 	put_ipc_ns(ns); /* paired with get_ipc_ns_not_zero */
  

  } }

• /* Remove the list head from any segments still attached. */
• list_del(&task->sysvshm.shm_clist);
• up_write(&shm_ids(ns).rwsem); }

static vm_fault_t shm_fault(struct vm_fault *vmf) @@ -680,7 +755,11 @@ static int newseg(struct ipc_namespace * if (error < 0) goto no_id;

• shp->ns = ns;
• task_lock(current); list_add(&shp->shm_clist, &current->sysvshm.shm_clist);
• task_unlock(current);

/* * shmid gets reported as "inode#" in /proc/pid/maps. @@ -1573,7 +1652,8 @@ out_nattch: down_write(&shm_ids(ns).rwsem); shp = shm_lock(ns, shmid); shp->shm_nattch--;

• if (shm_may_destroy(ns, shp))

• if (shm_may_destroy(shp)) shm_destroy(ns, shp); else shm_unlock(shp);

_

Patches currently in -mm which might be from alexander.mikhalitsyn@virtuozzo.com are

ipc-warn-if-trying-to-remove-ipc-object-which-is-absent.patch shm-extend-forced-shm-destroy-to-support-objects-from-several-ipc-nses.patch