diff options
author | Todd Kjos <tkjos@android.com> | 2019-06-05 09:37:46 -0700 |
---|---|---|
committer | Todd Kjos <tkjos@google.com> | 2019-06-12 11:32:26 -0700 |
commit | 1de5a484cfc3fff1b5631b76d59d5e5cd73bf7c1 (patch) | |
tree | a6540992029be065bf1902cb25e06a82ea373872 | |
parent | 0b33b35d88cfdb95876f6f3c56262b6583cf2c33 (diff) |
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.
Change-Id: I5f0d0333e81d1c377639a4b7c4900c00041448b8
Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Todd Kjos <tkjos@google.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: stable <stable@vger.kernel.org> # 4.14
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | drivers/android/binder_alloc.c | 18 |
1 files changed, 8 insertions, 10 deletions
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c index 1facfab25560..7874385c5748 100644 --- a/drivers/android/binder_alloc.c +++ b/drivers/android/binder_alloc.c @@ -922,14 +922,13 @@ 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 = alloc->vma; - 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); @@ -942,10 +941,9 @@ 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); |