io_uring: allow SQPOLL with CAP_SYS_NICE privileges

CAP_SYS_ADMIN is too restrictive for a lot of uses cases, allow
CAP_SYS_NICE based on the premise that such users are already allowed
to raise the priority of tasks.
Signed-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -7783,7 +7783,7 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 		struct io_sq_data *sqd;
 
 		ret = -EPERM;
-		if (!capable(CAP_SYS_ADMIN))
+		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_NICE))
 			goto err;
 
 		sqd = io_get_sq_data(p);