io_uring: restrict IORING_SETUP_SQPOLL to root

mainline inclusion
from mainline-5.1-rc5
commit 3ec482d1
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27
CVE: NA
---------------------------

This options spawns a kernel side thread that will poll for submissions
(and completions, if IORING_SETUP_IOPOLL is set). As this allows a user
to potentially use more cycles outside of the normal hierarchy,
restrict the use of this feature to root.
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NZhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Nyangerkun <yangerkun@huawei.com>
Reviewed-by: Nzhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

fs/io_uring.c

@@ -2242,6 +2242,10 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
 		goto err;
 
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		ret = -EPERM;
+		if (!capable(CAP_SYS_ADMIN))
+			goto err;
+
 		if (p->flags & IORING_SETUP_SQ_AFF) {
 			int cpu;