netdev - [PATCH] ncpfs: memory corruption in ncp_read

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Message-ID: <20180319110745.GA12001@mwanda>
Date:   Mon, 19 Mar 2018 14:07:45 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Petr Vandrovec <petr@...drovec.name>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "David S. Miller" <davem@...emloft.net>,
        devel@...verdev.osuosl.org, netdev@...r.kernel.org,
        security@...nel.org
Subject: [PATCH] ncpfs: memory corruption in ncp_read_kernel()

If the server is malicious then *bytes_read could be larger than the
size of the "target" buffer.  It would lead to memory corruption when we
do the memcpy().

Reported-by: Dr Silvio Cesare of InfoSect <Silvio Cesare <silvio.cesare@...il.com>
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>

diff --git a/drivers/staging/ncpfs/ncplib_kernel.c b/drivers/staging/ncpfs/ncplib_kernel.c
index 804adfebba2f..3e047eb4cc7c 100644
--- a/drivers/staging/ncpfs/ncplib_kernel.c
+++ b/drivers/staging/ncpfs/ncplib_kernel.c
@@ -981,6 +981,10 @@ ncp_read_kernel(struct ncp_server *server, const char *file_id,
 		goto out;
 	}
 	*bytes_read = ncp_reply_be16(server, 0);
+	if (*bytes_read > to_read) {
+		result = -EINVAL;
+		goto out;
+	}
 	source = ncp_reply_data(server, 2 + (offset & 1));
 
 	memcpy(target, source, *bytes_read);