scsi: block: Improve ioprio value validity checks

The introduction of the macro IOPRIO_PRIO_LEVEL() in commit eca2040972b4
("scsi: block: ioprio: Clean up interface definition") results in an
iopriority level to always be masked using the macro IOPRIO_LEVEL_MASK, and
thus to the kernel always seeing an acceptable value for an I/O priority
level when checked in ioprio_check_cap(). Before this patch, this function
would return an error for some (but not all) invalid values for a level
valid range of [0..7].

Restore and improve the detection of invalid priority levels by introducing
the inline function ioprio_value() to check an ioprio class, level and hint
value before combining these fields into a single value to be used with
ioprio_set() or AIOs. If an invalid value for the class, level or hint of
an ioprio is detected, ioprio_value() returns an ioprio using the class
IOPRIO_CLASS_INVALID, indicating an invalid value and causing
ioprio_check_cap() to return -EINVAL.

Fixes: 6c913257226a ("scsi: block: Introduce ioprio hints")
Fixes: eca2040972b4 ("scsi: block: ioprio: Clean up interface definition")
Signed-off-by: Damien Le Moal <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Niklas Cassel <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

block/ioprio.c

···
 			if (level)
 				return -EINVAL;
 			break;
+		case IOPRIO_CLASS_INVALID:
 		default:
 			return -EINVAL;
 	}

include/uapi/linux/ioprio.h

···
 #ifndef _UAPI_LINUX_IOPRIO_H
 #define _UAPI_LINUX_IOPRIO_H
 
+#include <linux/stddef.h>
+#include <linux/types.h>
+
 /*
  * Gives us 8 prio classes with 13-bits of data for each class
  */
 #define IOPRIO_CLASS_SHIFT	13
-#define IOPRIO_CLASS_MASK	0x07
+#define IOPRIO_NR_CLASSES	8
+#define IOPRIO_CLASS_MASK	(IOPRIO_NR_CLASSES - 1)
 #define IOPRIO_PRIO_MASK	((1UL << IOPRIO_CLASS_SHIFT) - 1)
 
 #define IOPRIO_PRIO_CLASS(ioprio)	\
 	(((ioprio) >> IOPRIO_CLASS_SHIFT) & IOPRIO_CLASS_MASK)
 #define IOPRIO_PRIO_DATA(ioprio)	((ioprio) & IOPRIO_PRIO_MASK)
-#define IOPRIO_PRIO_VALUE(class, data)	\
-	((((class) & IOPRIO_CLASS_MASK) << IOPRIO_CLASS_SHIFT) | \
-	 ((data) & IOPRIO_PRIO_MASK))
 
 /*
  * These are the io priority classes as implemented by the BFQ and mq-deadline
···
  * served when no one else is using the disk.
  */
 enum {
-	IOPRIO_CLASS_NONE,
-	IOPRIO_CLASS_RT,
-	IOPRIO_CLASS_BE,
-	IOPRIO_CLASS_IDLE,
+	IOPRIO_CLASS_NONE	= 0,
+	IOPRIO_CLASS_RT		= 1,
+	IOPRIO_CLASS_BE		= 2,
+	IOPRIO_CLASS_IDLE	= 3,
+
+	/* Special class to indicate an invalid ioprio value */
+	IOPRIO_CLASS_INVALID	= 7,
 };
 
 /*
···
 	(((ioprio) >> IOPRIO_HINT_SHIFT) & IOPRIO_HINT_MASK)
 
 /*
- * Alternate macro for IOPRIO_PRIO_VALUE() to define an I/O priority with
- * a class, level and hint.
- */
-#define IOPRIO_PRIO_VALUE_HINT(class, level, hint)		 \
-	((((class) & IOPRIO_CLASS_MASK) << IOPRIO_CLASS_SHIFT) | \
-	 (((hint) & IOPRIO_HINT_MASK) << IOPRIO_HINT_SHIFT) |	 \
-	 ((level) & IOPRIO_LEVEL_MASK))
-
-/*
  * I/O hints.
  */
 enum {
···
 	IOPRIO_HINT_DEV_DURATION_LIMIT_6 = 6,
 	IOPRIO_HINT_DEV_DURATION_LIMIT_7 = 7,
 };
+
+#define IOPRIO_BAD_VALUE(val, max) ((val) < 0 || (val) >= (max))
+
+/*
+ * Return an I/O priority value based on a class, a level and a hint.
+ */
+static __always_inline __u16 ioprio_value(int class, int level, int hint)
+{
+	if (IOPRIO_BAD_VALUE(class, IOPRIO_NR_CLASSES) ||
+	    IOPRIO_BAD_VALUE(level, IOPRIO_NR_LEVELS) ||
+	    IOPRIO_BAD_VALUE(hint, IOPRIO_NR_HINTS))
+		return IOPRIO_CLASS_INVALID << IOPRIO_CLASS_SHIFT;
+
+	return (class << IOPRIO_CLASS_SHIFT) |
+		(hint << IOPRIO_HINT_SHIFT) | level;
+}
+
+#define IOPRIO_PRIO_VALUE(class, level)			\
+	ioprio_value(class, level, IOPRIO_HINT_NONE)
+#define IOPRIO_PRIO_VALUE_HINT(class, level, hint)	\
+	ioprio_value(class, level, hint)
 
 #endif /* _UAPI_LINUX_IOPRIO_H */