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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,
        syzbot+ca8bf833622a1662745b@syzkaller.appspotmail.com,
        Dylan Yudaken <dylany@fb.com>, Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5.16 009/164] io_uring: disallow modification of rsrc_data during quiesce
Date:   Mon, 28 Feb 2022 18:22:51 +0100
Message-Id: <20220228172400.614445343@linuxfoundation.org>
In-Reply-To: <20220228172359.567256961@linuxfoundation.org>
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From: Dylan Yudaken <dylany@fb.com>

commit 80912cef18f16f8fe59d1fb9548d4364342be360 upstream.

io_rsrc_ref_quiesce will unlock the uring while it waits for references to
the io_rsrc_data to be killed.
There are other places to the data that might add references to data via
calls to io_rsrc_node_switch.
There is a race condition where this reference can be added after the
completion has been signalled. At this point the io_rsrc_ref_quiesce call
will wake up and relock the uring, assuming the data is unused and can be
freed - although it is actually being used.

To fix this check in io_rsrc_ref_quiesce if a resource has been revived.

Reported-by: syzbot+ca8bf833622a1662745b@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220222161751.995746-1-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/io_uring.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -7865,7 +7865,15 @@ static __cold int io_rsrc_ref_quiesce(st
 		ret = wait_for_completion_interruptible(&data->done);
 		if (!ret) {
 			mutex_lock(&ctx->uring_lock);
-			break;
+			if (atomic_read(&data->refs) > 0) {
+				/*
+				 * it has been revived by another thread while
+				 * we were unlocked
+				 */
+				mutex_unlock(&ctx->uring_lock);
+			} else {
+				break;
+			}
 		}
 
 		atomic_inc(&data->refs);