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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Pavel Begunkov <asml.silence@gmail.com>,
        Sasha Levin <sashal@kernel.org>,
        van fantasy <g1042620637@gmail.com>
Subject: [PATCH 5.18 067/141] io_uring: fix races with buffer table unregister
Date:   Mon, 20 Jun 2022 14:50:05 +0200
Message-Id: <20220620124731.519623762@linuxfoundation.org>
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From: Pavel Begunkov <asml.silence@gmail.com>

[ Upstream commit d11d31fc5d8a96f707facee0babdcffaafa38de2 ]

Fixed buffer table quiesce might unlock ->uring_lock, potentially
letting new requests to be submitted, don't allow those requests to
use the table as they will race with unregistration.

Reported-and-tested-by: van fantasy <g1042620637@gmail.com>
Fixes: bd54b6fe3316ec ("io_uring: implement fixed buffers registration similar to fixed files")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/io_uring.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0a9f9000fc80..3d123ca028c9 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -9495,12 +9495,19 @@ static void __io_sqe_buffers_unregister(struct io_ring_ctx *ctx)
 
 static int io_sqe_buffers_unregister(struct io_ring_ctx *ctx)
 {
+	unsigned nr = ctx->nr_user_bufs;
 	int ret;
 
 	if (!ctx->buf_data)
 		return -ENXIO;
 
+	/*
+	 * Quiesce may unlock ->uring_lock, and while it's not held
+	 * prevent new requests using the table.
+	 */
+	ctx->nr_user_bufs = 0;
 	ret = io_rsrc_ref_quiesce(ctx->buf_data, ctx);
+	ctx->nr_user_bufs = nr;
 	if (!ret)
 		__io_sqe_buffers_unregister(ctx);
 	return ret;
-- 
2.35.1