[PATCH 4.18 267/350] dm ioctl: harden copy_params()s copy_from_user() from malicious users

Greg Kroah-Hartman
2018-11-11T23:20:54Z

From: Wenwen Wang <wang6495@umn.edu>

commit 800a7340ab7dd667edf95e74d8e4f23a17e87076 upstream.

In copy_params(), the struct 'dm_ioctl' is first copied from the user
space buffer 'user' to 'param_kernel' and the field 'data_size' is
checked against 'minimum_data_size' (size of 'struct dm_ioctl' payload
up to its 'data' member). If the check fails, an error code EINVAL will be
returned. Otherwise, param_kernel->data_size is used to do a second copy,
which copies from the same user-space buffer to 'dmi'. After the second
copy, only 'dmi->data_size' is checked against 'param_kernel->data_size'.
Given that the buffer 'user' resides in the user space, a malicious
user-space process can race to change the content in the buffer between
the two copies. This way, the attacker can inject inconsistent data
into 'dmi' (versus previously validated 'param_kernel').

Fix redundant copying of 'minimum_data_size' from user-space buffer by
using the first copy stored in 'param_kernel'. Also remove the
'data_size' check after the second copy because it is now unnecessary.

Cc: stable@vger.kernel.org
Signed-off-by: Wenwen Wang <wang6495@umn.edu>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/dm-ioctl.c | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)

--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1720,8 +1720,7 @@ static void free_params(struct dm_ioctl
}

static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kernel,
- int ioctl_flags,
- struct dm_ioctl **param, int *param_flags)
+ int ioctl_flags, struct dm_ioctl **param, int *param_flags)
{
struct dm_ioctl *dmi;
int secure_data;
@@ -1762,18 +1761,13 @@ static int copy_params(struct dm_ioctl _

*param_flags |= DM_PARAMS_MALLOC;

- if (copy_from_user(dmi, user, param_kernel->data_size))
- goto bad;
+ /* Copy from param_kernel (which was already copied from user) */
+ memcpy(dmi, param_kernel, minimum_data_size);

-data_copied:
- /*
- * Abort if something changed the ioctl data while it was being copied.
- */
- if (dmi->data_size != param_kernel->data_size) {
- DMERR("rejecting ioctl: data size modified while processing parameters");
+ if (copy_from_user(&dmi->data, (char __user *)user + minimum_data_size,
+ param_kernel->data_size - minimum_data_size))
goto bad;
- }
-
+data_copied:
/* Wipe the user buffer so we do not return it to userspace */
if (secure_data && clear_user(user, param_kernel->data_size))
goto bad;