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binder: fix race between munmap() and direct reclaim

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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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Todd Kjos 2019-03-01 15:06:06 -08:00 committed by Greg Kroah-Hartman
parent 5997da8214
commit 5cec2d2e58
1 changed files with 8 additions and 10 deletions
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18
drivers/android/binder_alloc.c
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@ -927,14 +927,13 @@ 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_read_trylock(&mm->mmap_sem))
goto err_down_write_mmap_sem_failed;
}
list_lru_isolate(lru, item);
spin_unlock(lock);
@ -945,10 +944,9 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
zap_page_range(vma, page_addr, PAGE_SIZE);
trace_binder_unmap_user_end(alloc, index);
up_read(&mm->mmap_sem);
mmput(mm);
}
up_write(&mm->mmap_sem);
mmput(mm);
trace_binder_unmap_kernel_start(alloc, index);