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
incorrectly.
Untag the address before subtracting.
Reviewed-by: Kees Cook <keesc...@chromium.org>
Reviewed-by: Catalin Marinas <catalin.mari...@arm.com>
Signed-off-by: Andrey Konovalov <andreyk...@google.com>
---
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
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -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;
--
2.22.0.rc2.383.gf4fbbf30c2-goog
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