BACKPORT: binder: fix race between munmap() and direct reclaim

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.

Bug: 120025196
Change-Id: I2f3284d294326ec7736303374769640a1e028783
Cc: Ben Hutchings <>
Signed-off-by: Todd Kjos <>
Reviewed-by: Joel Fernandes (Google) <>
Cc: stable <> # 4.14
Signed-off-by: Greg Kroah-Hartman <>
1 file changed