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authorTodd Kjos <tkjos@android.com>2019-03-01 15:06:06 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-03-21 06:51:32 +0100
commit5cec2d2e5839f9c0fec319c523a911e0a7fd299f (patch)
tree84da718fce8d1beaecc8ac62c419f95da174db54 /drivers/android
parentbinder: fix BUG_ON found by selinux-testsuite (diff)
downloadlinux-dev-5cec2d2e5839f9c0fec319c523a911e0a7fd299f.tar.xz
linux-dev-5cec2d2e5839f9c0fec319c523a911e0a7fd299f.zip
binder: fix race between munmap() and direct reclaim
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>
Diffstat (limited to 'drivers/android')
-rw-r--r--drivers/android/binder_alloc.c18
1 files changed, 8 insertions, 10 deletions
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 6389467670a0..195f120c4e8c 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -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);