[PATCH] scsi: fix scsi_mode_sense()

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The allocation length field of the MODE SENSE 10 command is 16-bits,
occupying bytes 7 and 8 of the CDB. With this command, access to mode
pages larger than 255 bytes is thus possible. Make sure that
scsi_mode_sense() code reflects this by initializing the allocation
length field using put_unaligned_be16() instead of directly setting
only byte 8 of the CDB with the buffer length.

While at it, also fix the folowing:
* use get_unaligned_be16() to retrieve the mode data length and block
  descriptor length fields of the mode sense reply header instead of
  using an open coded calculation.
* Fix the kdoc dbd argument explanation: the DBD bit stands for
  Disable Block Descriptor, which is the opposite of what the dbd
  argument description was.

Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxx>
---
 drivers/scsi/scsi_lib.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 7456a26aef51..92db00d81733 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2070,7 +2070,7 @@ EXPORT_SYMBOL_GPL(scsi_mode_select);
 /**
  *	scsi_mode_sense - issue a mode sense, falling back from 10 to six bytes if necessary.
  *	@sdev:	SCSI device to be queried
- *	@dbd:	set if mode sense will allow block descriptors to be returned
+ *	@dbd:	set to prevent mode sense from returning block descriptors
  *	@modepage: mode page being requested
  *	@buffer: request buffer (may not be smaller than eight bytes)
  *	@len:	length of request buffer.
@@ -2112,7 +2112,7 @@ scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,
 			len = 8;
 
 		cmd[0] = MODE_SENSE_10;
-		cmd[8] = len;
+		put_unaligned_be16(len, &cmd[7]);
 		header_length = 8;
 	} else {
 		if (len < 4)
@@ -2166,12 +2166,11 @@ scsi_mode_sense(struct scsi_device *sdev, int dbd, int modepage,
 		data->longlba = 0;
 		data->block_descriptor_length = 0;
 	} else if (use_10_for_ms) {
-		data->length = buffer[0]*256 + buffer[1] + 2;
+		data->length = get_unaligned_be16(&buffer[0]) + 2;
 		data->medium_type = buffer[2];
 		data->device_specific = buffer[3];
 		data->longlba = buffer[4] & 0x01;
-		data->block_descriptor_length = buffer[6]*256
-			+ buffer[7];
+		data->block_descriptor_length = get_unaligned_be16(&buffer[6]);
 	} else {
 		data->length = buffer[0] + 1;
 		data->medium_type = buffer[1];
-- 
2.31.1




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