[PATCH] io_uring: async workers should inherit the user creds

[Jens Axboe <axboe@kernel.dk>]

If we don't inherit the original task creds, then we can confuse users
like fuse that pass creds in the request header. See link below on
identical aio issue.

Link: https://lore.kernel.org/linux-fsdevel/26f0d78e-99ca-2f1b-78b9-433088053a61@scylladb.com/T/#u
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 84efb8956734..9bead1717949 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -255,6 +255,8 @@ struct io_ring_ctx {
 
 	struct user_struct	*user;
 
+	struct cred		*creds;
+
 	struct completion	ctx_done;
 
 	struct {
@@ -1294,8 +1296,11 @@ static void io_poll_complete_work(struct work_struct *work)
 	struct io_poll_iocb *poll = &req->poll;
 	struct poll_table_struct pt = { ._key = poll->events };
 	struct io_ring_ctx *ctx = req->ctx;
+	const struct cred *old_cred;
 	__poll_t mask = 0;
 
+	old_cred = override_creds(ctx->creds);
+
 	if (!READ_ONCE(poll->canceled))
 		mask = vfs_poll(poll->file, &pt) & poll->events;
 
@@ -1310,7 +1315,7 @@ static void io_poll_complete_work(struct work_struct *work)
 	if (!mask && !READ_ONCE(poll->canceled)) {
 		add_wait_queue(poll->head, &poll->wait);
 		spin_unlock_irq(&ctx->completion_lock);
-		return;
+		goto out;
 	}
 	list_del_init(&req->list);
 	io_poll_complete(ctx, req, mask);
@@ -1318,6 +1323,8 @@ static void io_poll_complete_work(struct work_struct *work)
 
 	io_cqring_ev_posted(ctx);
 	io_put_req(req);
+out:
+	revert_creds(old_cred);
 }
 
 static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
@@ -1528,10 +1535,12 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 	struct io_ring_ctx *ctx = req->ctx;
 	struct mm_struct *cur_mm = NULL;
 	struct async_list *async_list;
+	const struct cred *old_cred;
 	LIST_HEAD(req_list);
 	mm_segment_t old_fs;
 	int ret;
 
+	old_cred = override_creds(ctx->creds);
 	async_list = io_async_list_from_sqe(ctx, req->submit.sqe);
 restart:
 	do {
@@ -1633,6 +1642,7 @@ static void io_sq_wq_submit_work(struct work_struct *work)
 		unuse_mm(cur_mm);
 		mmput(cur_mm);
 	}
+	revert_creds(old_cred);
 }
 
 /*
@@ -1881,6 +1891,7 @@ static int io_sq_thread(void *data)
 	struct sqe_submit sqes[IO_IOPOLL_BATCH];
 	struct io_ring_ctx *ctx = data;
 	struct mm_struct *cur_mm = NULL;
+	const struct cred *old_cred;
 	mm_segment_t old_fs;
 	DEFINE_WAIT(wait);
 	unsigned inflight;
@@ -1888,6 +1899,7 @@ static int io_sq_thread(void *data)
 
 	old_fs = get_fs();
 	set_fs(USER_DS);
+	old_cred = override_creds(ctx->creds);
 
 	timeout = inflight = 0;
 	while (!kthread_should_stop() && !ctx->sqo_stop) {
@@ -2001,6 +2013,7 @@ static int io_sq_thread(void *data)
 		unuse_mm(cur_mm);
 		mmput(cur_mm);
 	}
+	revert_creds(old_cred);
 
 	if (kthread_should_park())
 		kthread_parkme();
@@ -2645,6 +2658,8 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 		io_unaccount_mem(ctx->user,
 				ring_pages(ctx->sq_entries, ctx->cq_entries));
 	free_uid(ctx->user);
+	if (ctx->creds)
+		put_cred(ctx->creds);
 	kfree(ctx);
 }
 
@@ -2924,6 +2939,12 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
 	ctx->account_mem = account_mem;
 	ctx->user = user;
 
+	ctx->creds = prepare_creds();
+	if (!ctx->creds) {
+		ret = -ENOMEM;
+		goto err;
+	}
+
 	ret = io_allocate_scq_urings(ctx, p);
 	if (ret)
 		goto err;
-- 
2.24.0