io_uring: restrict IORING_SETUP_SQPOLL to root

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: Jens Axboe <axboe@kernel.dk>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 07d6ef195d05..89aa8412b5f5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2245,6 +2245,10 @@ 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;