[SCSI] sr.c: Fix getting wrong size

Here's the problem. Try to do this on 2.6.12:
- Kill udev and HAL
- Insert a CD-ROM into a SCSI or USB CD-ROM drive
- Run dd if=/dev/scd0
- cat /sys/block/sr0/size
- Eject the CD, insert a different one
- Run dd if=/dev/scd0
This is likely to do "access beyond the end of device", if you let it
- cat /sys/block/sr0/size
This shows the size of a previous CD, even though dd was supposed
to revalidate the device.
- Run dd if=/dev/scd0
The second run of dd works correctly!

The bug was introduced in 2.5.31, when Al fixes the recursive opens
in partitioning. Before, the code worked like this:
- Block layer called cdrom_open directly
- cdrom_open called sr_open
- sr_open called check_disk_change
- check_disk_change called sr_media_change
- sr_media_change did cd->needs_disk_change=1
- before returning sr_open tested cd->needs_disk_change
  and called get_sector_size.

In 2.6.12, the check_disk_change is called from cdrom_open only. Thus:
- Block layer calls sr_bd_open
- sr_bd_open calls cdrom_open
- cdrom_open calls sr_open
- sr_open tests cd->needs_disk_change, which wasn't set yet; returns
- cdrom_open calls check_disk_change
- check_disk_change calls sr_media_change
- sr_media_change does cd->needs_disk_change=1, but nobody cares

Acked by: Alexander Viro <aviro@redhat.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

2 files changed, 2 insertions, 23 deletions

diff --git a/drivers/scsi/sr.c b/drivers/scsi/sr.c
index 2f259f249522..f63d8c6c2a33 100644
--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -199,15 +199,7 @@ int sr_media_change(struct cdrom_device_info *cdi, int slot)
                 /* check multisession offset etc */
                 sr_cd_check(cdi);
 
-                /* 
-                 * If the disk changed, the capacity will now be different,
-                 * so we force a re-read of this information 
-                 * Force 2048 for the sector size so that filesystems won't
-                 * be trying to use something that is too small if the disc
-                 * has changed.
-                 */
-                cd->needs_sector_size = 1;
-                cd->device->sector_size = 2048;
+                get_sectorsize(cd);
         }
         return retval;
 }
@@ -538,13 +530,6 @@ static int sr_open(struct cdrom_device_info *cdi, int purpose)
         if (!scsi_block_when_processing_errors(sdev))
                 goto error_out;
 
-        /*
-         * If this device did not have media in the drive at boot time, then
-         * we would have been unable to get the sector size.  Check to see if
-         * this is the case, and try again.
-         */
-        if (cd->needs_sector_size)
-                get_sectorsize(cd);
         return 0;
 
 error_out:
@@ -604,7 +589,6 @@ static int sr_probe(struct device *dev)
         cd->driver = &sr_template;
         cd->disk = disk;
         cd->capacity = 0x1fffff;
-        cd->needs_sector_size = 1;
         cd->device->changed = 1;        /* force recheck CD type */
         cd->use = 1;
         cd->readcd_known = 0;
@@ -694,7 +678,6 @@ static void get_sectorsize(struct scsi_cd *cd)
         if (the_result) {
                 cd->capacity = 0x1fffff;
                 sector_size = 2048;     /* A guess, just in case */
-                cd->needs_sector_size = 1;
         } else {
 #if 0
                 if (cdrom_get_last_written(&cd->cdi,
@@ -727,7 +710,6 @@ static void get_sectorsize(struct scsi_cd *cd)
                         printk("%s: unsupported sector size %d.\n",
                                cd->cdi.name, sector_size);
                         cd->capacity = 0;
-                        cd->needs_sector_size = 1;
                 }
 
                 cd->device->sector_size = sector_size;
@@ -736,7 +718,6 @@ static void get_sectorsize(struct scsi_cd *cd)
                  * Add this so that we have the ability to correctly gauge
                  * what the device is capable of.
                  */
-                cd->needs_sector_size = 0;
                 set_capacity(cd->disk, cd->capacity);
         }
 
@@ -748,8 +729,7 @@ out:
 
 Enomem:
         cd->capacity = 0x1fffff;
-        sector_size = 2048;     /* A guess, just in case */
-        cd->needs_sector_size = 1;
+        cd->device->sector_size = 2048; /* A guess, just in case */
         if (SRpnt)
                 scsi_release_request(SRpnt);
         goto out;
diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h
index 0b3178007203..d2bcd99c272f 100644
--- a/drivers/scsi/sr.h
+++ b/drivers/scsi/sr.h
@@ -33,7 +33,6 @@ typedef struct scsi_cd {
         struct scsi_device *device;
         unsigned int vendor;    /* vendor code, see sr_vendor.c         */
         unsigned long ms_offset;        /* for reading multisession-CD's        */
-        unsigned needs_sector_size:1;   /* needs to get sector size */
         unsigned use:1;         /* is this device still supportable     */
         unsigned xa_flag:1;     /* CD has XA sectors ? */
         unsigned readcd_known:1;        /* drive supports READ_CD (0xbe) */