block: sed-opal: handle empty atoms when parsing response

The SED Opal response parsing function response_parse() does not
handle the case of an empty atom in the response. This causes
the entry count to be too high and the response fails to be
parsed. Recognizing, but ignoring, empty atoms allows response
handling to succeed.

Signed-off-by: Greg Joyce <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

block/opal_proto.h

···
 #define SHORT_ATOM_BYTE  0xBF
 #define MEDIUM_ATOM_BYTE 0xDF
 #define LONG_ATOM_BYTE   0xE3
+#define EMPTY_ATOM_BYTE  0xFF
 
 #define OPAL_INVAL_PARAM 12
 #define OPAL_MANUFACTURED_INACTIVE 0x08

block/sed-opal.c

···
 			token_length = response_parse_medium(iter, pos);
 		else if (pos[0] <= LONG_ATOM_BYTE) /* long atom */
 			token_length = response_parse_long(iter, pos);
+		else if (pos[0] == EMPTY_ATOM_BYTE) /* empty atom */
+			token_length = 1;
 		else /* TOKEN */
 			token_length = response_parse_token(iter, pos);
 
 		if (token_length < 0)
 			return token_length;
 
+		if (pos[0] != EMPTY_ATOM_BYTE)
+			num_entries++;
+
 		pos += token_length;
 		total -= token_length;
 		iter++;
-		num_entries++;
 	}
 
 	resp->num = num_entries;