[to-be-updated] shm-skip-shm_destroy-if-task-ipc-namespace-was-changed.patch removed from -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: shm: skip shm_destroy if task IPC namespace was changed
has been removed from the -mm tree.  Its filename was
     shm-skip-shm_destroy-if-task-ipc-namespace-was-changed.patch

This patch was dropped because an updated version will be merged

------------------------------------------------------
From: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
Subject: shm: skip shm_destroy if task IPC namespace was changed

Patch series "shm: omit forced shm destroy if task IPC namespace was changed".

Task IPC namespace shm's has shm_rmid_forced feature which is per IPC
namespace and controlled by kernel.shm_rmid_forced sysctl.  When feature
is turned on, then during task exit (and unshare(CLONE_NEWIPC)) all
sysvshm's will be destroyed by exit_shm(struct task_struct *task)
function.

But there is a problem if task was changed IPC namespace since shmget()
call.  In such situation exit_shm() function will try to call
shm_destroy(<new_ipc_namespace_ptr>, <sysvshmem_from_old_ipc_namespace>)
which leads to the situation when sysvshm object still attached to old IPC
namespace but freed; later during old IPC namespace cleanup we will try to
free such sysvshm object for the second time and will get the problem :)

First patch solves this problem by postponing shm_destroy to the moment
when IPC namespace cleanup will be called.  Second patch is useful to
prevent (or easy catch) such bugs in the future by adding corresponding
WARNings.


This patch (of 2):

Task may change IPC namespace by doing setns() but sysvshm objects remains
at the origin IPC namespace (=IPC namespace where task was when shmget()
was called).  Let's skip forced shm destroy in such case because we can't
determine IPC namespace by shm only.  These problematic sysvshm's will be
destroyed on ipc namespace cleanup.

Link: https://lkml.kernel.org/r/20210706132259.71740-1-alexander.mikhalitsyn@virtuozzo.com
Link: https://lkml.kernel.org/r/20210706132259.71740-2-alexander.mikhalitsyn@virtuozzo.com
Fixes: ab602f79915 ("shm: make exit_shm work proportional to task activity")
Signed-off-by: Alexander Mikhalitsyn <alexander.mikhalitsyn@virtuozzo.com>
Cc: Milton Miller <miltonm@bga.com>
Cc: Jack Miller <millerjo@us.ibm.com>
Cc: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: Alexander Mikhalitsyn <alexander@mihalicyn.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 ipc/shm.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/ipc/shm.c~shm-skip-shm_destroy-if-task-ipc-namespace-was-changed
+++ a/ipc/shm.c
@@ -173,6 +173,14 @@ static inline struct shmid_kernel *shm_o
 	return container_of(ipcp, struct shmid_kernel, shm_perm);
 }
 
+static inline bool is_shm_in_ns(struct ipc_namespace *ns, struct shmid_kernel *shp)
+{
+	int idx = ipcid_to_idx(shp->shm_perm.id);
+	struct shmid_kernel *tshp = shm_obtain_object(ns, idx);
+
+	return !IS_ERR(tshp) && tshp == shp;
+}
+
 /*
  * shm_lock_(check_) routines are called in the paths where the rwsem
  * is not necessarily held.
@@ -415,7 +423,7 @@ void exit_shm(struct task_struct *task)
 	list_for_each_entry_safe(shp, n, &task->sysvshm.shm_clist, shm_clist) {
 		shp->shm_creator = NULL;
 
-		if (shm_may_destroy(ns, shp)) {
+		if (is_shm_in_ns(ns, shp) && shm_may_destroy(ns, shp)) {
 			shm_lock_by_ptr(shp);
 			shm_destroy(ns, 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