dm io:ctl use constant struct size

Make size of dm_ioctl struct always 312 bytes on all supported
architectures.

This change retains compatibility with already-compiled code because
it uses an embedded offset to locate the payload that follows the
structure.

On 64-bit architectures there is no change at all; on 32-bit
we are increasing the size of dm-ioctl from 308 to 312 bytes.

Currently with 32-bit userspace / 64-bit kernel on x86_64
some ioctls (including rename, message) are incorrectly rejected
by the comparison against 'param + 1'.  This breaks userspace
lvrename and multipath 'fail_if_no_path' changes, for example.

(BTW Device-mapper uses its own versioning and ignores the ioctl
size bits.  Only the generic ioctl compat code on mixed arches
checks them, and that will continue to accept both sizes for now,
but we intend to list 308 as deprecated and eventually remove it.)

Signed-off-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: Guido Guenther <agx@sigxcpu.org>
Cc: Kevin Corry <kevcorry@us.ibm.com>
Cc: stable@kernel.org

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index b441d82c338a..ba5d8f7cc5f2 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -700,7 +700,7 @@ static int dev_rename(struct dm_ioctl *param, size_t param_size)
         int r;
         char *new_name = (char *) param + param->data_start;
 
-        if (new_name < (char *) (param + 1) ||
+        if (new_name < (char *) param->data ||
             invalid_str(new_name, (void *) param + param_size)) {
                 DMWARN("Invalid new logical volume name supplied.");
                 return -EINVAL;
@@ -726,7 +726,7 @@ static int dev_set_geometry(struct dm_ioctl *param, size_t param_size)
         if (!md)
                 return -ENXIO;
 
-        if (geostr < (char *) (param + 1) ||
+        if (geostr < (char *) param->data ||
             invalid_str(geostr, (void *) param + param_size)) {
                 DMWARN("Invalid geometry supplied.");
                 goto out;
@@ -1233,7 +1233,7 @@ static int target_message(struct dm_ioctl *param, size_t param_size)
         if (r)
                 goto out;
 
-        if (tmsg < (struct dm_target_msg *) (param + 1) ||
+        if (tmsg < (struct dm_target_msg *) param->data ||
             invalid_str(tmsg->message, (void *) param + param_size)) {
                 DMWARN("Invalid target message parameters.");
                 r = -EINVAL;