linux-kernel - [PATCH] android: binder: Fix a possible data race in binder_alloc_mmap

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Date:   Tue,  8 May 2018 17:06:39 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     gregkh@...uxfoundation.org, arve@...roid.com, tkjos@...roid.com,
        maco@...roid.com
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@...il.com>
Subject: [PATCH] android: binder: Fix a possible data race in binder_alloc_mmap_handler

The write operations to "alloc->buffer" are protected by
the lock on line 679 and 730, but the read operation to
this data on line 712 is not protected by the lock.
Thus, there may exist a data race for "alloc->buffer".

To fix this data race, the read operation to "alloc->buffer" 
should be also protected by the lock.

Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
---
 drivers/android/binder_alloc.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index 5a426c877dfb..596acc3a84e4 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -709,7 +709,9 @@ int binder_alloc_mmap_handler(struct binder_alloc *alloc,
 		goto err_alloc_buf_struct_failed;
 	}
 
+	mutex_lock(&binder_alloc_mmap_lock);
 	buffer->data = alloc->buffer;
+	mutex_unlock(&binder_alloc_mmap_lock);
 	list_add(&buffer->entry, &alloc->buffers);
 	buffer->free = 1;
 	binder_insert_free_buffer(alloc, buffer);
-- 
2.17.0