md: check command validity early in md_ioctl().

Verify that the cmd parameter passed to md_ioctl() is valid before
doing anything.

This fixes mddev->hold_active being set to 0 when an invalid ioctl
command is passed to md_ioctl() before the array has been configured.

Clearing mddev->hold_active in that case can lead to a livelock
situation when an invalid ioctl number is given to md_ioctl() by a
process when the mddev is currently being opened by another process:

Process 1				Process 2
---------				---------

md_alloc()
  mddev_find()
  -> returns a new mddev with
     hold_active == UNTIL_IOCTL
  add_disk()
  -> sends KOBJ_ADD uevent

					(sees KOBJ_ADD uevent for device)
                    			md_open()
                    			md_ioctl(INVALID_IOCTL)
                    			-> returns ENODEV and clears
                       			   mddev->hold_active
                    			md_release()
                      			md_put()
                      			-> deletes the mddev as
                         		   hold_active is 0

md_open()
  mddev_find()
  -> returns a newly
    allocated mddev with
    mddev->gendisk == NULL
-> returns with ERESTARTSYS
   (kernel restarts the open syscall)

Signed-off-by: Nicolas Schichan <nschichan@freebox.fr>
Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 29 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index a20b7806de7a..b890d3fb0e02 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6356,6 +6356,32 @@ static int md_getgeo(struct block_device *bdev, struct hd_geometry *geo)
         return 0;
 }
 
+static inline bool md_ioctl_valid(unsigned int cmd)
+{
+        switch (cmd) {
+        case ADD_NEW_DISK:
+        case BLKROSET:
+        case GET_ARRAY_INFO:
+        case GET_BITMAP_FILE:
+        case GET_DISK_INFO:
+        case HOT_ADD_DISK:
+        case HOT_REMOVE_DISK:
+        case PRINT_RAID_DEBUG:
+        case RAID_AUTORUN:
+        case RAID_VERSION:
+        case RESTART_ARRAY_RW:
+        case RUN_ARRAY:
+        case SET_ARRAY_INFO:
+        case SET_BITMAP_FILE:
+        case SET_DISK_FAULTY:
+        case STOP_ARRAY:
+        case STOP_ARRAY_RO:
+                return true;
+        default:
+                return false;
+        }
+}
+
 static int md_ioctl(struct block_device *bdev, fmode_t mode,
                         unsigned int cmd, unsigned long arg)
 {
@@ -6364,6 +6390,9 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
         struct mddev *mddev = NULL;
         int ro;
 
+        if (!md_ioctl_valid(cmd))
+                return -ENOTTY;
+
         switch (cmd) {
         case RAID_VERSION:
         case GET_ARRAY_INFO: