[PATCH v10 06/12] fs, arm64: untag user pointers in copy_mount_options

From: Andrey Konovalov
Date: Fri Feb 22 2019 - 07:54:23 EST


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@xxxxxxxxxx>
---
fs/namespace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index a677b59efd74..d4b7adef9204 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2730,7 +2730,7 @@ 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;

--
2.21.0.rc0.258.g878e2cd30e-goog