FAILED: patch "[PATCH] io_uring: fix leaking reg files on exit" failed to apply to 5.12-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 084804002e512427bfe52b448cb7cac0d4209b64 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Tue, 13 Apr 2021 02:58:38 +0100
Subject: [PATCH] io_uring: fix leaking reg files on exit

If io_sqe_files_unregister() faults on io_rsrc_ref_quiesce(), it will
fail to do unregister leaving files referenced. And that may well happen
because of a strayed signal or just because it does allocations inside.

In io_ring_ctx_free() do an unsafe version of unregister, as it's
guaranteed to not have requests by that point and so quiesce is useless.

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/e696e9eade571b51997d0dc1d01f144c6d685c05.1618278933.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 8564c7908126..1af8bb5f7d56 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7089,6 +7089,10 @@ static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
 			fput(file);
 	}
 #endif
+	io_free_file_tables(&ctx->file_table, ctx->nr_user_files);
+	kfree(ctx->file_data);
+	ctx->file_data = NULL;
+	ctx->nr_user_files = 0;
 }
 
 static inline void io_rsrc_ref_lock(struct io_ring_ctx *ctx)
@@ -7195,21 +7199,14 @@ static struct io_rsrc_data *io_rsrc_data_alloc(struct io_ring_ctx *ctx,
 
 static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
 {
-	struct io_rsrc_data *data = ctx->file_data;
 	int ret;
 
-	if (!data)
+	if (!ctx->file_data)
 		return -ENXIO;
-	ret = io_rsrc_ref_quiesce(data, ctx);
-	if (ret)
-		return ret;
-
-	__io_sqe_files_unregister(ctx);
-	io_free_file_tables(&ctx->file_table, ctx->nr_user_files);
-	kfree(data);
-	ctx->file_data = NULL;
-	ctx->nr_user_files = 0;
-	return 0;
+	ret = io_rsrc_ref_quiesce(ctx->file_data, ctx);
+	if (!ret)
+		__io_sqe_files_unregister(ctx);
+	return ret;
 }
 
 static void io_sq_thread_unpark(struct io_sq_data *sqd)
@@ -7659,7 +7656,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 
 	ret = io_sqe_files_scm(ctx);
 	if (ret) {
-		io_sqe_files_unregister(ctx);
+		__io_sqe_files_unregister(ctx);
 		return ret;
 	}
 
@@ -8460,7 +8457,11 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
 	}
 
 	mutex_lock(&ctx->uring_lock);
-	io_sqe_files_unregister(ctx);
+	if (ctx->file_data) {
+		if (!atomic_dec_and_test(&ctx->file_data->refs))
+			wait_for_completion(&ctx->file_data->done);
+		__io_sqe_files_unregister(ctx);
+	}
 	if (ctx->rings)
 		__io_cqring_overflow_flush(ctx, true);
 	mutex_unlock(&ctx->uring_lock);