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authorMichal Hocko <mhocko@suse.com>2017-12-14 15:33:15 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2017-12-14 16:00:49 -0800
commit4837fe37adff1d159904f0c013471b1ecbcb455e (patch)
tree169fb195798dbf1afb20a87d32681230116157ce
parentbdcf0a423ea1c40bbb40e7ee483b50fc8aa3d758 (diff)
downloadlinux-4837fe37adff1d159904f0c013471b1ecbcb455e.tar.bz2
mm, oom_reaper: fix memory corruption
David Rientjes has reported the following memory corruption while the oom reaper tries to unmap the victims address space BUG: Bad page map in process oom_reaper pte:6353826300000000 pmd:00000000 addr:00007f50cab1d000 vm_flags:08100073 anon_vma:ffff9eea335603f0 mapping: (null) index:7f50cab1d file: (null) fault: (null) mmap: (null) readpage: (null) CPU: 2 PID: 1001 Comm: oom_reaper Call Trace: unmap_page_range+0x1068/0x1130 __oom_reap_task_mm+0xd5/0x16b oom_reaper+0xff/0x14c kthread+0xc1/0xe0 Tetsuo Handa has noticed that the synchronization inside exit_mmap is insufficient. We only synchronize with the oom reaper if tsk_is_oom_victim which is not true if the final __mmput is called from a different context than the oom victim exit path. This can trivially happen from context of any task which has grabbed mm reference (e.g. to read /proc/<pid>/ file which requires mm etc.). The race would look like this oom_reaper oom_victim task mmget_not_zero do_exit mmput __oom_reap_task_mm mmput __mmput exit_mmap remove_vma unmap_page_range Fix this issue by providing a new mm_is_oom_victim() helper which operates on the mm struct rather than a task. Any context which operates on a remote mm struct should use this helper in place of tsk_is_oom_victim. The flag is set in mark_oom_victim and never cleared so it is stable in the exit_mmap path. Debugged by Tetsuo Handa. Link: http://lkml.kernel.org/r/20171210095130.17110-1-mhocko@kernel.org Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently") Signed-off-by: Michal Hocko <mhocko@suse.com> Reported-by: David Rientjes <rientjes@google.com> Acked-by: David Rientjes <rientjes@google.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Andrea Argangeli <andrea@kernel.org> Cc: <stable@vger.kernel.org> [4.14] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/oom.h9
-rw-r--r--include/linux/sched/coredump.h1
-rw-r--r--mm/mmap.c10
-rw-r--r--mm/oom_kill.c4
4 files changed, 18 insertions, 6 deletions
diff --git a/include/linux/oom.h b/include/linux/oom.h
index 01c91d874a57..5bad038ac012 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -67,6 +67,15 @@ static inline bool tsk_is_oom_victim(struct task_struct * tsk)
}
/*
+ * Use this helper if tsk->mm != mm and the victim mm needs a special
+ * handling. This is guaranteed to stay true after once set.
+ */
+static inline bool mm_is_oom_victim(struct mm_struct *mm)
+{
+ return test_bit(MMF_OOM_VICTIM, &mm->flags);
+}
+
+/*
* Checks whether a page fault on the given mm is still reliable.
* This is no longer true if the oom reaper started to reap the
* address space which is reflected by MMF_UNSTABLE flag set in
diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
index 9c8847395b5e..ec912d01126f 100644
--- a/include/linux/sched/coredump.h
+++ b/include/linux/sched/coredump.h
@@ -70,6 +70,7 @@ static inline int get_dumpable(struct mm_struct *mm)
#define MMF_UNSTABLE 22 /* mm is unstable for copy_from_user */
#define MMF_HUGE_ZERO_PAGE 23 /* mm has ever used the global huge zero page */
#define MMF_DISABLE_THP 24 /* disable THP for all VMAs */
+#define MMF_OOM_VICTIM 25 /* mm is the oom victim */
#define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP)
#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\
diff --git a/mm/mmap.c b/mm/mmap.c
index a4d546821214..9efdc021ad22 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3019,20 +3019,20 @@ void exit_mmap(struct mm_struct *mm)
/* Use -1 here to ensure all VMAs in the mm are unmapped */
unmap_vmas(&tlb, vma, 0, -1);
- set_bit(MMF_OOM_SKIP, &mm->flags);
- if (unlikely(tsk_is_oom_victim(current))) {
+ if (unlikely(mm_is_oom_victim(mm))) {
/*
* Wait for oom_reap_task() to stop working on this
* mm. Because MMF_OOM_SKIP is already set before
* calling down_read(), oom_reap_task() will not run
* on this "mm" post up_write().
*
- * tsk_is_oom_victim() cannot be set from under us
- * either because current->mm is already set to NULL
+ * mm_is_oom_victim() cannot be set from under us
+ * either because victim->mm is already set to NULL
* under task_lock before calling mmput and oom_mm is
- * set not NULL by the OOM killer only if current->mm
+ * set not NULL by the OOM killer only if victim->mm
* is found not NULL while holding the task_lock.
*/
+ set_bit(MMF_OOM_SKIP, &mm->flags);
down_write(&mm->mmap_sem);
up_write(&mm->mmap_sem);
}
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index c957be32b27a..29f855551efe 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -683,8 +683,10 @@ static void mark_oom_victim(struct task_struct *tsk)
return;
/* oom_mm is bound to the signal struct life time. */
- if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm))
+ if (!cmpxchg(&tsk->signal->oom_mm, NULL, mm)) {
mmgrab(tsk->signal->oom_mm);
+ set_bit(MMF_OOM_VICTIM, &mm->flags);
+ }
/*
* Make sure that the task is woken up from uninterruptible sleep