Commit 800a7340 authored Oct 03, 2018 by Wenwen Wang Committed by Mike Snitzer Oct 18, 2018

dm ioctl: harden copy_params()'s copy_from_user() from malicious users



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>

parent bab5d988

drivers/md/dm-ioctl.c

+6 −12

Original line number	Diff line number	Diff line
		@@ -1720,8 +1720,7 @@ static void free_params(struct dm_ioctl *param, size_t param_size, int param_fla
		}

		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 __user user, struct dm_ioctl param_kern

		*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;

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