[PATCH v16 08/16] fs, arm64: untag user pointers in copy_mount_options
From: Andrey Konovalov
Date: Mon Jun 03 2019 - 12:59:43 EST
This patch is a part of a series that extends arm64 kernel ABI to allow to
pass tagged user pointers (with the top byte set to something else other
than 0x00) as syscall arguments.
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
Untag the address before subtracting.
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
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 b26778bdc236..2e85712a19ed 100644
@@ -2993,7 +2993,7 @@ 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;