From: Todd Kjos tkjos@android.com

commit 5cec2d2e5839f9c0fec319c523a911e0a7fd299f upstream.

An munmap() on a binder device causes binder_vma_close() to be called which clears the alloc->vma pointer.

If direct reclaim causes binder_alloc_free_page() to be called, there is a race where alloc->vma is read into a local vma pointer and then used later after the mm->mmap_sem is acquired. This can result in calling zap_page_range() with an invalid vma which manifests as a use-after-free in zap_page_range().

The fix is to check alloc->vma after acquiring the mmap_sem (which we were acquiring anyway) and skip zap_page_range() if it has changed to NULL.

Signed-off-by: Todd Kjos tkjos@google.com Reviewed-by: Joel Fernandes (Google) joel@joelfernandes.org Cc: stable stable@vger.kernel.org # 5.0, 4.19, 4.14 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Greg: This applies to 5.0, 4.19, 4.14. Not needed before 4.12.

drivers/android/binder_alloc.c | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 022cd80e80cc..a6e556bf62df 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -959,14 +959,13 @@ enum lru_status binder_alloc_free_page(struct list_head *item,

index = page - alloc->pages; page_addr = (uintptr_t)alloc->buffer + index * PAGE_SIZE; + + mm = alloc->vma_vm_mm; + if (!mmget_not_zero(mm)) + goto err_mmget; + if (!down_write_trylock(&mm->mmap_sem)) + goto err_down_write_mmap_sem_failed; vma = binder_alloc_get_vma(alloc); - if (vma) { - if (!mmget_not_zero(alloc->vma_vm_mm)) - goto err_mmget; - mm = alloc->vma_vm_mm; - if (!down_write_trylock(&mm->mmap_sem)) - goto err_down_write_mmap_sem_failed; - }

list_lru_isolate(lru, item); spin_unlock(lock); @@ -979,10 +978,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item, PAGE_SIZE);

trace_binder_unmap_user_end(alloc, index); - - up_write(&mm->mmap_sem); - mmput(mm); } + up_write(&mm->mmap_sem); + mmput(mm);

trace_binder_unmap_kernel_start(alloc, index);