On Sat, Jun 8, 2019 at 6:02 AM Kees Cook [off-list ref] wrote:

On Mon, Jun 03, 2019 at 06:55:10PM +0200, Andrey Konovalov wrote:

quoted

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: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrey Konovalov <redacted>

One thing I just noticed in the commit titles... "arm64" is in the
prefix, but these are arch-indep areas. Should the ", arm64" be left
out?

I would expect, instead:

        fs/namespace: untag user pointers in copy_mount_options

Hm, I've added the arm64 tag in all of the patches because they are
related to changes in arm64 kernel ABI. I can remove it from all the
patches that only touch common code if you think that it makes sense.

Thanks!

Reviewed-by: Kees Cook <redacted>

-Kees

quoted

---
 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.rc1.311.g5d7573a151-goog

--
Kees Cook

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel