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authorDavid Rientjes <rientjes@google.com>2018-05-12 02:02:04 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-05-12 03:28:45 +0300
commit27ae357fa82be5ab73b2ef8d39dcb8ca2563483a (patch)
tree78596e2b24c4923f8d17152ac23b15d2d7681c19
parent013567be19761e2d14fc2a2676fe7686ac54c9ac (diff)
downloadlinux-sunxi-27ae357fa82be5ab73b2ef8d39dcb8ca2563483a.tar.xz
mm, oom: fix concurrent munlock and oom reaper unmap, v3
Since exit_mmap() is done without the protection of mm->mmap_sem, it is possible for the oom reaper to concurrently operate on an mm until MMF_OOM_SKIP is set. This allows munlock_vma_pages_all() to concurrently run while the oom reaper is operating on a vma. Since munlock_vma_pages_range() depends on clearing VM_LOCKED from vm_flags before actually doing the munlock to determine if any other vmas are locking the same memory, the check for VM_LOCKED in the oom reaper is racy. This is especially noticeable on architectures such as powerpc where clearing a huge pmd requires serialize_against_pte_lookup(). If the pmd is zapped by the oom reaper during follow_page_mask() after the check for pmd_none() is bypassed, this ends up deferencing a NULL ptl or a kernel oops. Fix this by manually freeing all possible memory from the mm before doing the munlock and then setting MMF_OOM_SKIP. The oom reaper can not run on the mm anymore so the munlock is safe to do in exit_mmap(). It also matches the logic that the oom reaper currently uses for determining when to set MMF_OOM_SKIP itself, so there's no new risk of excessive oom killing. This issue fixes CVE-2018-1000200. Link: http://lkml.kernel.org/r/alpine.DEB.2.21.1804241526320.238665@chino.kir.corp.google.com Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently") Signed-off-by: David Rientjes <rientjes@google.com> Suggested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Andrea Arcangeli <aarcange@redhat.com> 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.h2
-rw-r--r--mm/mmap.c44
-rw-r--r--mm/oom_kill.c81
3 files changed, 71 insertions, 56 deletions
diff --git a/include/linux/oom.h b/include/linux/oom.h
index 5bad038ac012..6adac113e96d 100644
--- a/include/linux/oom.h
+++ b/include/linux/oom.h
@@ -95,6 +95,8 @@ static inline int check_stable_address_space(struct mm_struct *mm)
return 0;
}
+void __oom_reap_task_mm(struct mm_struct *mm);
+
extern unsigned long oom_badness(struct task_struct *p,
struct mem_cgroup *memcg, const nodemask_t *nodemask,
unsigned long totalpages);
diff --git a/mm/mmap.c b/mm/mmap.c
index 9d5968d1e8e3..d6836566e4e5 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3024,6 +3024,32 @@ void exit_mmap(struct mm_struct *mm)
/* mm's last user has gone, and its about to be pulled down */
mmu_notifier_release(mm);
+ if (unlikely(mm_is_oom_victim(mm))) {
+ /*
+ * Manually reap the mm to free as much memory as possible.
+ * Then, as the oom reaper does, set MMF_OOM_SKIP to disregard
+ * this mm from further consideration. Taking mm->mmap_sem for
+ * write after setting MMF_OOM_SKIP will guarantee that the oom
+ * reaper will not run on this mm again after mmap_sem is
+ * dropped.
+ *
+ * Nothing can be holding mm->mmap_sem here and the above call
+ * to mmu_notifier_release(mm) ensures mmu notifier callbacks in
+ * __oom_reap_task_mm() will not block.
+ *
+ * This needs to be done before calling munlock_vma_pages_all(),
+ * which clears VM_LOCKED, otherwise the oom reaper cannot
+ * reliably test it.
+ */
+ mutex_lock(&oom_lock);
+ __oom_reap_task_mm(mm);
+ mutex_unlock(&oom_lock);
+
+ set_bit(MMF_OOM_SKIP, &mm->flags);
+ down_write(&mm->mmap_sem);
+ up_write(&mm->mmap_sem);
+ }
+
if (mm->locked_vm) {
vma = mm->mmap;
while (vma) {
@@ -3045,24 +3071,6 @@ void exit_mmap(struct mm_struct *mm)
/* update_hiwater_rss(mm) here? but nobody should be looking */
/* Use -1 here to ensure all VMAs in the mm are unmapped */
unmap_vmas(&tlb, vma, 0, -1);
-
- 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().
- *
- * 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 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);
- }
free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb, 0, -1);
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index ff992fa8760a..8ba6cb88cf58 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -469,7 +469,6 @@ bool process_shares_mm(struct task_struct *p, struct mm_struct *mm)
return false;
}
-
#ifdef CONFIG_MMU
/*
* OOM Reaper kernel thread which tries to reap the memory used by the OOM
@@ -480,16 +479,54 @@ static DECLARE_WAIT_QUEUE_HEAD(oom_reaper_wait);
static struct task_struct *oom_reaper_list;
static DEFINE_SPINLOCK(oom_reaper_lock);
-static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
+void __oom_reap_task_mm(struct mm_struct *mm)
{
- struct mmu_gather tlb;
struct vm_area_struct *vma;
+
+ /*
+ * Tell all users of get_user/copy_from_user etc... that the content
+ * is no longer stable. No barriers really needed because unmapping
+ * should imply barriers already and the reader would hit a page fault
+ * if it stumbled over a reaped memory.
+ */
+ set_bit(MMF_UNSTABLE, &mm->flags);
+
+ for (vma = mm->mmap ; vma; vma = vma->vm_next) {
+ if (!can_madv_dontneed_vma(vma))
+ continue;
+
+ /*
+ * Only anonymous pages have a good chance to be dropped
+ * without additional steps which we cannot afford as we
+ * are OOM already.
+ *
+ * We do not even care about fs backed pages because all
+ * which are reclaimable have already been reclaimed and
+ * we do not want to block exit_mmap by keeping mm ref
+ * count elevated without a good reason.
+ */
+ if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
+ const unsigned long start = vma->vm_start;
+ const unsigned long end = vma->vm_end;
+ struct mmu_gather tlb;
+
+ tlb_gather_mmu(&tlb, mm, start, end);
+ mmu_notifier_invalidate_range_start(mm, start, end);
+ unmap_page_range(&tlb, vma, start, end, NULL);
+ mmu_notifier_invalidate_range_end(mm, start, end);
+ tlb_finish_mmu(&tlb, start, end);
+ }
+ }
+}
+
+static bool oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
+{
bool ret = true;
/*
* We have to make sure to not race with the victim exit path
* and cause premature new oom victim selection:
- * __oom_reap_task_mm exit_mm
+ * oom_reap_task_mm exit_mm
* mmget_not_zero
* mmput
* atomic_dec_and_test
@@ -534,39 +571,8 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
trace_start_task_reaping(tsk->pid);
- /*
- * Tell all users of get_user/copy_from_user etc... that the content
- * is no longer stable. No barriers really needed because unmapping
- * should imply barriers already and the reader would hit a page fault
- * if it stumbled over a reaped memory.
- */
- set_bit(MMF_UNSTABLE, &mm->flags);
-
- for (vma = mm->mmap ; vma; vma = vma->vm_next) {
- if (!can_madv_dontneed_vma(vma))
- continue;
+ __oom_reap_task_mm(mm);
- /*
- * Only anonymous pages have a good chance to be dropped
- * without additional steps which we cannot afford as we
- * are OOM already.
- *
- * We do not even care about fs backed pages because all
- * which are reclaimable have already been reclaimed and
- * we do not want to block exit_mmap by keeping mm ref
- * count elevated without a good reason.
- */
- if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
- const unsigned long start = vma->vm_start;
- const unsigned long end = vma->vm_end;
-
- tlb_gather_mmu(&tlb, mm, start, end);
- mmu_notifier_invalidate_range_start(mm, start, end);
- unmap_page_range(&tlb, vma, start, end, NULL);
- mmu_notifier_invalidate_range_end(mm, start, end);
- tlb_finish_mmu(&tlb, start, end);
- }
- }
pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
task_pid_nr(tsk), tsk->comm,
K(get_mm_counter(mm, MM_ANONPAGES)),
@@ -587,14 +593,13 @@ static void oom_reap_task(struct task_struct *tsk)
struct mm_struct *mm = tsk->signal->oom_mm;
/* Retry the down_read_trylock(mmap_sem) a few times */
- while (attempts++ < MAX_OOM_REAP_RETRIES && !__oom_reap_task_mm(tsk, mm))
+ while (attempts++ < MAX_OOM_REAP_RETRIES && !oom_reap_task_mm(tsk, mm))
schedule_timeout_idle(HZ/10);
if (attempts <= MAX_OOM_REAP_RETRIES ||
test_bit(MMF_OOM_SKIP, &mm->flags))
goto done;
-
pr_info("oom_reaper: unable to reap pid:%d (%s)\n",
task_pid_nr(tsk), tsk->comm);
debug_show_all_locks();