From b4a72c0589fdea6259720375426179888969d6a2 Mon Sep 17 00:00:00 2001
From: Wojciech Lukowicz <wlukowicz01@gmail.com>
Date: Sat, 1 Apr 2023 20:50:39 +0100
Subject: [PATCH] io_uring: fix memory leak when removing provided buffers
Git-commit: b4a72c0589fdea6259720375426179888969d6a2
Patch-mainline: v6.3-rc6
References: git-fixes

When removing provided buffers, io_buffer structs are not being disposed
of, leading to a memory leak. They can't be freed individually, because
they are allocated in page-sized groups. They need to be added to some
free list instead, such as io_buffers_cache. All callers already hold
the lock protecting it, apart from when destroying buffers, so had to
extend the lock there.

Fixes: cc3cec8367cb ("io_uring: speedup provided buffer handling")
Signed-off-by: Wojciech Lukowicz <wlukowicz01@gmail.com>
Link: https://lore.kernel.org/r/20230401195039.404909-2-wlukowicz01@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
 fs/io_uring.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5324,11 +5324,14 @@ static int __io_remove_buffers(struct io
 		return i;
 	}
 
+	/* protects io_buffers_cache */
+	lockdep_assert_held(&ctx->uring_lock);
+
 	while (!list_empty(&bl->buf_list)) {
 		struct io_buffer *nxt;
 
 		nxt = list_first_entry(&bl->buf_list, struct io_buffer, list);
-		list_del(&nxt->list);
+		list_move(&nxt->list, &ctx->io_buffers_cache);
 		if (++i == nbufs)
 			return i;
 		cond_resched();
@@ -10846,8 +10849,8 @@ static __cold void io_ring_ctx_free(stru
 		__io_cqring_overflow_flush(ctx, true);
 	io_eventfd_unregister(ctx);
 	io_flush_apoll_cache(ctx);
-	mutex_unlock(&ctx->uring_lock);
 	io_destroy_buffers(ctx);
+	mutex_unlock(&ctx->uring_lock);
 	if (ctx->sq_creds)
 		put_cred(ctx->sq_creds);