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

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/shm-skip-shm_destroy-if-task-ipc-n... and later at https://ozlabs.org/~akpm/mmotm/broken-out/shm-skip-shm_destroy-if-task-ipc-n...

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------------------------------------------------------ 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@virtu... Link: https://lkml.kernel.org/r/20210706132259.71740-2-alexander.mikhalitsyn@virtu... 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

shm-skip-shm_destroy-if-task-ipc-namespace-was-changed.patch ipc-warn-if-trying-to-remove-ipc-object-which-is-absent.patch