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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, Xie Yongji <xieyongji@bytedance.com>,
        Fam Zheng <fam.zheng@bytedance.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 157/167] vringh: Fix loop descriptors check in the indirect cases
Date:   Mon, 13 Jun 2022 12:10:31 +0200
Message-Id: <20220613094917.736801133@linuxfoundation.org>
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From: Xie Yongji <xieyongji@bytedance.com>

[ Upstream commit dbd29e0752286af74243cf891accf472b2f3edd8 ]

We should use size of descriptor chain to test loop condition
in the indirect case. And another statistical count is also introduced
for indirect descriptors to avoid conflict with the statistical count
of direct descriptors.

Fixes: f87d0fbb5798 ("vringh: host-side implementation of virtio rings.")
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Signed-off-by: Fam Zheng <fam.zheng@bytedance.com>
Message-Id: <20220505100910.137-1-xieyongji@bytedance.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/vhost/vringh.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index da47542496cc..63f0ab3e6f63 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -262,7 +262,7 @@ __vringh_iov(struct vringh *vrh, u16 i,
 	     gfp_t gfp,
 	     int (*copy)(void *dst, const void *src, size_t len))
 {
-	int err, count = 0, up_next, desc_max;
+	int err, count = 0, indirect_count = 0, up_next, desc_max;
 	struct vring_desc desc, *descs;
 	struct vringh_range range = { -1ULL, 0 }, slowrange;
 	bool slow = false;
@@ -319,7 +319,12 @@ __vringh_iov(struct vringh *vrh, u16 i,
 			continue;
 		}
 
-		if (count++ == vrh->vring.num) {
+		if (up_next == -1)
+			count++;
+		else
+			indirect_count++;
+
+		if (count > vrh->vring.num || indirect_count > desc_max) {
 			vringh_bad("Descriptor loop in %p", descs);
 			err = -ELOOP;
 			goto fail;
@@ -381,6 +386,7 @@ __vringh_iov(struct vringh *vrh, u16 i,
 				i = return_from_indirect(vrh, &up_next,
 							 &descs, &desc_max);
 				slow = false;
+				indirect_count = 0;
 			} else
 				break;
 		}
-- 
2.35.1