io_uring: round-up cq size before comparing with rounded sq size

If an application specifies IORING_SETUP_CQSIZE to set the CQ ring size
to a specific size, we ensure that the CQ size is at least that of the
SQ ring size. But in doing so, we compare the already rounded up to power
of two SQ size to the as-of yet unrounded CQ size. This means that if an
application passes in non power of two sizes, we can return -EINVAL when
the final value would've been fine. As an example, an application passing
in 100/100 for sq/cq size should end up with 128 for both. But since we
round the SQ size first, we compare the CQ size of 100 to 128, and return
-EINVAL as that is too small.

Cc: [email protected]
Fixes: 33a107f ("io_uring: allow application controlled CQ ring size")
Reported-by: Dan Melnic <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

fs/io_uring.c

@@ -9226,14 +9226,14 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p,
 		 * to a power-of-two, if it isn't already. We do NOT impose
 		 * any cq vs sq ring sizing.
 		 */
+		p->cq_entries = roundup_pow_of_two(p->cq_entries);
 		if (p->cq_entries < p->sq_entries)
 			return -EINVAL;
 		if (p->cq_entries > IORING_MAX_CQ_ENTRIES) {
 			if (!(p->flags & IORING_SETUP_CLAMP))
 				return -EINVAL;
 			p->cq_entries = IORING_MAX_CQ_ENTRIES;
 		}
-		p->cq_entries = roundup_pow_of_two(p->cq_entries);
 	} else {
 		p->cq_entries = 2 * p->sq_entries;
 	}