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8619236d93
commit 85b6d24646e4125c591639841169baa98a2da503 upstream. Currently, the 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). This is an 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 a 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 can we 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: No. 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/67bb03e5-f79c-1815-e2bf-949c67047418@colorfullife.com Link: https://lkml.kernel.org/r/20211109151501.4921-1-manfred@colorfullife.com 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> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
75 lines
1.7 KiB
C
75 lines
1.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_SHM_H_
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#define _LINUX_SHM_H_
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#include <linux/list.h>
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#include <asm/page.h>
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#include <uapi/linux/shm.h>
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#include <asm/shmparam.h>
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struct shmid_kernel /* private to the kernel */
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{
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struct kern_ipc_perm shm_perm;
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struct file *shm_file;
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unsigned long shm_nattch;
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unsigned long shm_segsz;
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time64_t shm_atim;
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time64_t shm_dtim;
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time64_t shm_ctim;
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pid_t shm_cprid;
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pid_t shm_lprid;
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struct user_struct *mlock_user;
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/*
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* The task created the shm object, for
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* task_lock(shp->shm_creator)
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*/
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struct task_struct *shm_creator;
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/*
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* List by creator. task_lock(->shm_creator) required for read/write.
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* If list_empty(), then the creator is dead already.
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*/
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struct list_head shm_clist;
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struct ipc_namespace *ns;
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} __randomize_layout;
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/* shm_mode upper byte flags */
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#define SHM_DEST 01000 /* segment will be destroyed on last detach */
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#define SHM_LOCKED 02000 /* segment will not be swapped */
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#ifdef CONFIG_SYSVIPC
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struct sysv_shm {
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struct list_head shm_clist;
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};
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long do_shmat(int shmid, char __user *shmaddr, int shmflg, unsigned long *addr,
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unsigned long shmlba);
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bool is_file_shm_hugepages(struct file *file);
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void exit_shm(struct task_struct *task);
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#define shm_init_task(task) INIT_LIST_HEAD(&(task)->sysvshm.shm_clist)
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#else
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struct sysv_shm {
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/* empty */
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};
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static inline long do_shmat(int shmid, char __user *shmaddr,
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int shmflg, unsigned long *addr,
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unsigned long shmlba)
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{
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return -ENOSYS;
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}
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static inline bool is_file_shm_hugepages(struct file *file)
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{
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return false;
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}
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static inline void exit_shm(struct task_struct *task)
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{
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}
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static inline void shm_init_task(struct task_struct *task)
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{
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}
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#endif
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#endif /* _LINUX_SHM_H_ */
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