linux-kernel - [PATCH 5.12 004/677] io_uring: truncate lengths larger than MAX_RW

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Message-Id: <20210512144837.353140128@linuxfoundation.org>
Date:   Wed, 12 May 2021 16:40:50 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 5.12 004/677] io_uring: truncate lengths larger than MAX_RW_COUNT on provide buffers

From: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>

commit d1f82808877bb10d3deee7cf3374a4eb3fb582db upstream.

Read and write operations are capped to MAX_RW_COUNT. Some read ops rely on
that limit, and that is not guaranteed by the IORING_OP_PROVIDE_BUFFERS.

Truncate those lengths when doing io_add_buffers, so buffer addresses still
use the uncapped length.

Also, take the chance and change struct io_buffer len member to __u32, so
it matches struct io_provide_buffer len member.

This fixes CVE-2021-3491, also reported as ZDI-CAN-13546.

Fixes: ddf0322db79c ("io_uring: add IORING_OP_PROVIDE_BUFFERS")
Reported-by: Billy Jheng Bing-Jhong (@st424204)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/io_uring.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -238,7 +238,7 @@ struct fixed_rsrc_data {
 struct io_buffer {
 	struct list_head list;
 	__u64 addr;
-	__s32 len;
+	__u32 len;
 	__u16 bid;
 };
 
@@ -4017,7 +4017,7 @@ static int io_add_buffers(struct io_prov
 			break;
 
 		buf->addr = addr;
-		buf->len = pbuf->len;
+		buf->len = min_t(__u32, pbuf->len, MAX_RW_COUNT);
 		buf->bid = bid;
 		addr += pbuf->len;
 		bid++;