From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 25 Nov 2019 08:52:30 -0700
Subject: io_uring: async workers should inherit the user creds
Git-commit: 181e448d8709e517c9c7b523fcd209f24eb38ca7
Patch-mainline: v5.5-rc1
References: CVE-2019-19241 bsc#1159441 bnc#1151927 5.3.15

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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 fs/io_uring.c |   23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -260,6 +260,8 @@ struct io_ring_ctx {
 
 	struct user_struct	*user;
 
+	struct cred		*creds;
+
 	struct completion	ctx_done;
 
 	struct {
@@ -1633,8 +1635,11 @@ static void io_poll_complete_work(struct
 	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;
 
@@ -1649,7 +1654,7 @@ static void io_poll_complete_work(struct
 	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);
@@ -1657,6 +1662,8 @@ static void io_poll_complete_work(struct
 
 	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,
@@ -1906,10 +1913,12 @@ static void io_sq_wq_submit_work(struct
 	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 {
@@ -2017,6 +2026,7 @@ out:
 		unuse_mm(cur_mm);
 		mmput(cur_mm);
 	}
+	revert_creds(old_cred);
 }
 
 /*
@@ -2358,6 +2368,7 @@ static int io_sq_thread(void *data)
 {
 	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;
@@ -2367,6 +2378,7 @@ 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_park()) {
@@ -2466,6 +2478,7 @@ static int io_sq_thread(void *data)
 		unuse_mm(cur_mm);
 		mmput(cur_mm);
 	}
+	revert_creds(old_cred);
 
 	kthread_parkme();
 
@@ -3135,6 +3148,8 @@ static void io_ring_ctx_free(struct io_r
 		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);
 }
 
@@ -3412,6 +3427,12 @@ static int io_uring_create(unsigned entr
 	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;