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From:   Andrey Konovalov <andreyknvl@google.com>
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Subject: [PATCH v6 07/11] fs, arm64: untag user address in copy_mount_options
Date:   Thu, 30 Aug 2018 13:41:12 +0200
Message-Id: <89806bc1c1f85fa97c62887075cc2d46b8bdeee2.1535629099.git.andreyknvl@google.com>
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In copy_mount_options a user address is being subtracted from TASK_SIZE.
If the address is lower than TASK_SIZE, the size is calculated to not
allow the exact_copy_from_user() call to cross TASK_SIZE boundary.
However if the address is tagged, then the size will be calculated
incorrectly.

Untag the address before subtracting.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 fs/namespace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index 99186556f8d3..51f763fb9430 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2672,7 +2672,7 @@ void *copy_mount_options(const void __user * data)
 	 * the remainder of the page.
 	 */
 	/* copy_from_user cannot cross TASK_SIZE ! */
-	size = TASK_SIZE - (unsigned long)data;
+	size = TASK_SIZE - (unsigned long)untagged_addr(data);
 	if (size > PAGE_SIZE)
 		size = PAGE_SIZE;
 
-- 
2.19.0.rc0.228.g281dcd1b4d0-goog