commit f868120549fc1664b2c451d4b9882a363928c698
author Milan Broz <mbroz@redhat.com> Thu Mar 24 13:54:30 2011 +0000
committer Alasdair G Kergon <agk@redhat.com> Thu Mar 24 13:54:30 2011 +0000
tree 20d95a8f3b9fac1348bd42a5ff1e3f9d43918b93
parent 6bb43b5d1f54fb44c0408d86d5e71e4405a3ebe1

dm ioctl: add flag to wipe buffers for secure data

Add DM_SECURE_DATA_FLAG which userspace can use to ensure
that all buffers allocated for dm-ioctl are wiped
immediately after use.

The user buffer is wiped as well (we do not want to keep
and return sensitive data back to userspace if the flag is set).

Wiping is useful for cryptsetup to ensure that the key
is present in memory only in defined places and only
for the time needed.

(For crypt, key can be present in table during load or table
status, wait and message commands).

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-ioctl.c

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 3a8f6a0..4cacdad 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1504,6 +1504,7 @@
 static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl **param)
 {
 	struct dm_ioctl tmp, *dmi;
+	int secure_data;
 
 	if (copy_from_user(&tmp, user, sizeof(tmp) - sizeof(tmp.data)))
 		return -EFAULT;
@@ -1511,17 +1512,28 @@
 	if (tmp.data_size < (sizeof(tmp) - sizeof(tmp.data)))
 		return -EINVAL;
 
+	secure_data = tmp.flags & DM_SECURE_DATA_FLAG;
+
 	dmi = vmalloc(tmp.data_size);
-	if (!dmi)
+	if (!dmi) {
+		if (secure_data && clear_user(user, tmp.data_size))
+			return -EFAULT;
 		return -ENOMEM;
+	}
 
 	if (copy_from_user(dmi, user, tmp.data_size))
 		goto bad;
 
+	/* Wipe the user buffer so we do not return it to userspace */
+	if (secure_data && clear_user(user, tmp.data_size))
+		goto bad;
+
 	*param = dmi;
 	return 0;
 
 bad:
+	if (secure_data)
+		memset(dmi, 0, tmp.data_size);
 	vfree(dmi);
 	return -EFAULT;
 }
@@ -1531,6 +1543,7 @@
 	/* Always clear this flag */
 	param->flags &= ~DM_BUFFER_FULL_FLAG;
 	param->flags &= ~DM_UEVENT_GENERATED_FLAG;
+	param->flags &= ~DM_SECURE_DATA_FLAG;
 
 	/* Ignores parameters */
 	if (cmd == DM_REMOVE_ALL_CMD ||
@@ -1558,6 +1571,7 @@
 static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
 {
 	int r = 0;
+	int wipe_buffer;
 	unsigned int cmd;
 	struct dm_ioctl *uninitialized_var(param);
 	ioctl_fn fn = NULL;
@@ -1602,13 +1616,15 @@
 	 * Copy the parameters into kernel space.
 	 */
 	r = copy_params(user, &param);
-	input_param_size = param->data_size;
 
 	current->flags &= ~PF_MEMALLOC;
 
 	if (r)
 		return r;
 
+	input_param_size = param->data_size;
+	wipe_buffer = param->flags & DM_SECURE_DATA_FLAG;
+
 	r = validate_params(cmd, param);
 	if (r)
 		goto out;
@@ -1623,6 +1639,9 @@
 		r = -EFAULT;
 
 out:
+	if (wipe_buffer)
+		memset(param, 0, input_param_size);
+
 	vfree(param);
 	return r;
 }