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From:   Andres Beltran <lkmlabelt@gmail.com>
To:     kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org
Cc:     linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        mikelley@microsoft.com, parri.andrea@gmail.com,
        skarade@microsoft.com, Andres Beltran <lkmlabelt@gmail.com>
Subject: [PATCH] Drivers: hv: vmbus: Fix variable assignments in hv_ringbuffer_read()
Date:   Fri, 24 Jul 2020 12:46:06 -0400
Message-Id: <20200724164606.43699-1-lkmlabelt@gmail.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Assignments to buffer_actual_len and requestid happen before packetlen
is checked to be within buflen. If this condition is true,
hv_ringbuffer_read() returns with these variables already set to some
value even though no data is actually read. This might create
inconsistencies in any routine calling hv_ringbuffer_read(). Assign values
to such pointers after the packetlen check.

Signed-off-by: Andres Beltran <lkmlabelt@gmail.com>
---
 drivers/hv/ring_buffer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 356e22159e83..e277ce7372a4 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -350,12 +350,13 @@ int hv_ringbuffer_read(struct vmbus_channel *channel,
 
 	offset = raw ? 0 : (desc->offset8 << 3);
 	packetlen = (desc->len8 << 3) - offset;
-	*buffer_actual_len = packetlen;
-	*requestid = desc->trans_id;
 
 	if (unlikely(packetlen > buflen))
 		return -ENOBUFS;
 
+	*buffer_actual_len = packetlen;
+	*requestid = desc->trans_id;
+
 	/* since ring is double mapped, only one copy is necessary */
 	memcpy(buffer, (const char *)desc + offset, packetlen);
 
-- 
2.25.1