[PATCH 2/2] 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-wq.c    | 10 ++++++++++
 fs/io-wq.h    |  1 +
 fs/io_uring.c | 14 ++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 49ca58c714da..85c0090b2717 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -57,6 +57,7 @@ struct io_worker {
 
 	struct rcu_head rcu;
 	struct mm_struct *mm;
+	const struct cred *creds;
 	struct files_struct *restore_files;
 };
 
@@ -111,6 +112,7 @@ struct io_wq {
 
 	struct task_struct *manager;
 	struct user_struct *user;
+	struct cred *creds;
 	struct mm_struct *mm;
 	refcount_t refs;
 	struct completion done;
@@ -136,6 +138,11 @@ static bool __io_worker_unuse(struct io_wqe *wqe, struct io_worker *worker)
 {
 	bool dropped_lock = false;
 
+	if (worker->creds) {
+		revert_creds(worker->creds);
+		worker->creds = NULL;
+	}
+
 	if (current->files != worker->restore_files) {
 		__acquire(&wqe->lock);
 		spin_unlock_irq(&wqe->lock);
@@ -442,6 +449,8 @@ static void io_worker_handle_work(struct io_worker *worker)
 			set_fs(USER_DS);
 			worker->mm = wq->mm;
 		}
+		if (!worker->creds)
+			worker->creds = override_creds(wq->creds);
 		if (test_bit(IO_WQ_BIT_CANCEL, &wq->state))
 			work->flags |= IO_WQ_WORK_CANCEL;
 		if (worker->mm)
@@ -995,6 +1004,7 @@ struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
 
 	/* caller must already hold a reference to this */
 	wq->user = data->user;
+	wq->creds = data->creds;
 
 	i = 0;
 	for_each_online_node(node) {
diff --git a/fs/io-wq.h b/fs/io-wq.h
index 6db81f0f44e2..e09c6a54648c 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -51,6 +51,7 @@ typedef void (put_work_fn)(struct io_wq_work *);
 struct io_wq_data {
 	struct mm_struct *mm;
 	struct user_struct *user;
+	struct cred *creds;
 
 	get_work_fn *get_work;
 	put_work_fn *put_work;
diff --git a/fs/io_uring.c b/fs/io_uring.c
index a9a1fb9954cc..26bfba729a1e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -237,6 +237,8 @@ struct io_ring_ctx {
 
 	struct user_struct	*user;
 
+	struct cred		*creds;
+
 	/* 0 is for ctx quiesce/reinit/free, 1 is for sqo_thread started */
 	struct completion	*completions;
 
@@ -3251,6 +3253,7 @@ 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;
@@ -3261,6 +3264,7 @@ static int io_sq_thread(void *data)
 
 	old_fs = get_fs();
 	set_fs(USER_DS);
+	old_cred = override_creds(ctx->creds);
 
 	ret = timeout = inflight = 0;
 	while (!kthread_should_park()) {
@@ -3367,6 +3371,7 @@ static int io_sq_thread(void *data)
 		unuse_mm(cur_mm);
 		mmput(cur_mm);
 	}
+	revert_creds(old_cred);
 
 	kthread_parkme();
 
@@ -3993,6 +3998,7 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
 
 	data.mm = ctx->sqo_mm;
 	data.user = ctx->user;
+	data.creds = ctx->creds;
 	data.get_work = io_get_work;
 	data.put_work = io_put_work;
 
@@ -4347,6 +4353,8 @@ 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->completions);
 	kmem_cache_free(req_cachep, ctx->fallback_req);
 	kfree(ctx);
@@ -4700,6 +4708,12 @@ 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