[PATCH 1/2] scsi: scsi_debug: wrap around the store when zeroing a reset zone

[Tal Zussman <tz2294@columbia.edu>]

zbc_rwp_zone() zeroes the blocks of a zone that is reset, using the
start of the zone as an offset into the store. With virtual_gb set, the
device and its zones can extend past the end of the store, which is
only dev_size_mb in size. Writes wrap around in do_device_access(), but
the memset() doesn't, so resetting a zone that has been written to can
write past the end of the store.

On a device whose fifth zone starts exactly at the end of the store,
write to that zone and reset it:

  # modprobe scsi_debug zbc=managed sector_size=4096 dev_size_mb=16 \
        virtual_gb=1 zone_size_mb=4
  # dd if=/dev/urandom of=/dev/sda bs=1M count=1 seek=16 oflag=direct
  # blkzone reset -o 32768 -c 1 /dev/sda

The memset() starts at the first byte past the store, in the guard page
after the vmalloc'ed area, for the 1 MiB that was written:

BUG: unable to handle page fault for address: ffffc90002c00000
Oops: Oops: 0002 [#1] SMP KASAN NOPTI
RIP: 0010:memset_orig+0x33/0xb0
RDX: 0000000000100000 RSI: 0000000000000000 RDI: ffffc90002c00000
Call Trace:
 zbc_rwp_zone+0x1a7/0x2a0 [scsi_debug]
 resp_rwp_zone+0x19c/0x450 [scsi_debug]
 schedule_resp+0x2dd/0xbc0 [scsi_debug]
 scsi_debug_queuecommand+0x1286/0x2950 [scsi_debug]
 scsi_queue_rq+0x1d74/0x3200
 blk_mq_dispatch_rq_list+0x3ad/0x23c0

The command never completes, so the reset returns EIO to userspace and
the device is unusable afterwards.

Zero the blocks in a helper that wraps around at the end of the store,
and that stops after one pass over it for a zone that is larger than
the store.

Fixes: f0d1cf9378bd ("scsi: scsi_debug: Add ZBC zone commands")
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
 drivers/scsi/scsi_debug.c | 26 ++++++++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index a922c8318a2f..1c27ea0f9b69 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -6612,6 +6612,29 @@ static int resp_finish_zone(struct scsi_cmnd *scp,
 	return res;
 }
 
+/*
+ * Zero the blocks of a zone that is being reset. The store can be smaller
+ * than the device, so wrap around at its end like do_device_access() does.
+ */
+static void zbc_zero_blocks(struct sdeb_store_info *sip, sector_t lba,
+			    sector_t num)
+{
+	/* One pass over the store zeroes all of it */
+	num = min_t(sector_t, num, sdebug_store_sectors);
+
+	while (num) {
+		sector_t block = lba;
+		u32 n;
+
+		block = sector_div(block, sdebug_store_sectors);
+		n = min_t(sector_t, num, sdebug_store_sectors - block);
+		memset(sip->storep + block * sdebug_sector_size, 0,
+		       (size_t)n * sdebug_sector_size);
+		lba += n;
+		num -= n;
+	}
+}
+
 static void zbc_rwp_zone(struct sdebug_dev_info *devip,
 			 struct sdeb_zone_state *zsp)
 {
@@ -6629,8 +6652,7 @@ static void zbc_rwp_zone(struct sdebug_dev_info *devip,
 		devip->nr_closed--;
 
 	if (zsp->z_wp > zsp->z_start)
-		memset(sip->storep + zsp->z_start * sdebug_sector_size, 0,
-		       (zsp->z_wp - zsp->z_start) * sdebug_sector_size);
+		zbc_zero_blocks(sip, zsp->z_start, zsp->z_wp - zsp->z_start);
 
 	zsp->z_non_seq_resource = false;
 	zsp->z_wp = zsp->z_start;

-- 
2.39.5