[PATCH v15 09/17] fs, arm64: untag user pointers in copy_mount_options
andreyknvl at google.com
Mon May 6 16:30:55 UTC 2019
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.
Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
fs/namespace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index c9cab307fa77..c27e5713bf04 100644
@@ -2825,7 +2825,7 @@ 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;
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