From: Todd Kjos <tk...@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.
Cc: Ben Hutchings <ben.hutchi...@codethink.co.uk>
Signed-off-by: Todd Kjos <tk...@google.com>
Reviewed-by: Joel Fernandes (Google) <j...@joelfernandes.org>
Cc: stable <sta...@vger.kernel.org> # 4.14
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
drivers/android/binder_alloc.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -945,14 +945,13 @@ enum lru_status binder_alloc_free_page(s
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);
@@ -965,10 +964,9 @@ enum lru_status binder_alloc_free_page(s
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);
