block: fix IOPRIO_PRIO_CLASS() and IOPRIO_PRIO_VALUE() macros

The ki_ioprio field of struct kiocb is 16-bits (u16) but often handled
as an int in the block layer. E.g. ioprio_check_cap() takes an int as
argument.

With such implicit int casting function calls, the upper 16-bits of the
int argument may be left uninitialized by the compiler, resulting in
invalid values for the IOPRIO_PRIO_CLASS() macro (garbage upper bits)
and in an error return for functions such as ioprio_check_cap().

Fix this by masking the result of the shift by IOPRIO_CLASS_SHIFT bits
in the IOPRIO_PRIO_CLASS() macro. The new macro IOPRIO_CLASS_MASK
defines the 3-bits mask for the priority class.
Similarly, apply the IOPRIO_PRIO_MASK mask to the data argument of the
IOPRIO_PRIO_VALUE() macro to ignore the upper bits of the data value.
The IOPRIO_CLASS_MASK mask is also applied to the class argument of this
macro before shifting the result by IOPRIO_CLASS_SHIFT bits.

While at it, also change the argument name of the IOPRIO_PRIO_CLASS()
and IOPRIO_PRIO_DATA() macros from "mask" to "ioprio" to reflect the
fact that a priority value should be passed rather than a mask.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Link: https://lore.kernel.org/r/20210811033702.368488-5-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 8 insertions, 4 deletions

diff --git a/include/uapi/linux/ioprio.h b/include/uapi/linux/ioprio.h
index 5064e230374c..936f0d8f30e1 100644
--- a/include/uapi/linux/ioprio.h
+++ b/include/uapi/linux/ioprio.h
@@ -5,12 +5,16 @@
 /*
  * Gives us 8 prio classes with 13-bits of data for each class
  */
-#define IOPRIO_CLASS_SHIFT	(13)
+#define IOPRIO_CLASS_SHIFT	13
+#define IOPRIO_CLASS_MASK	0x07
 #define IOPRIO_PRIO_MASK	((1UL << IOPRIO_CLASS_SHIFT) - 1)
 
-#define IOPRIO_PRIO_CLASS(mask)	((mask) >> IOPRIO_CLASS_SHIFT)
-#define IOPRIO_PRIO_DATA(mask)	((mask) & IOPRIO_PRIO_MASK)
-#define IOPRIO_PRIO_VALUE(class, data)	(((class) << IOPRIO_CLASS_SHIFT) | data)
+#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 groups as implemented by the BFQ and mq-deadline