netdev - [PATCH net] net/x25: prevent a couple of overflows

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Date:   Mon, 30 Nov 2020 13:04:25 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Andrew Hendry <andrew.hendry@...il.com>,
        kiyin(尹亮) <kiyin@...cent.com>,
        Martin Schiller <ms@....tdt.de>
Cc:     "security@...nel.org" <security@...nel.org>,
        "linux-distros@...openwall.org" <linux-distros@...openwall.org>,
        huntchen(陈阳) <huntchen@...cent.com>,
        dannywang(王宇) <dannywang@...cent.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-x25@...r.kernel.org,
        netdev@...r.kernel.org
Subject: [PATCH net] net/x25: prevent a couple of overflows

From: "kiyin(尹亮)" <kiyin@...cent.com>

The .x25_addr[] address comes from the user and is not necessarily
NUL terminated.  This leads to a couple problems.  The first problem is
that the strlen() in x25_bind() can read beyond the end of the buffer.

The second problem is more subtle and could result in memory corruption.
The call tree is:
  x25_connect()
  --> x25_write_internal()
      --> x25_addr_aton()

The .x25_addr[] buffers are copied to the "addresses" buffer from
x25_write_internal() so it will lead to stack corruption.

The x25 protocol only allows 15 character addresses so putting a NUL
terminator as the 16th character is safe and obviously preferable to
reading out of bounds.

Signed-off-by: "kiyin(尹亮)" <kiyin@...cent.com>
Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
---

 net/x25/af_x25.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/x25/af_x25.c b/net/x25/af_x25.c
index 0bbb283f23c9..3180f15942fe 100644
--- a/net/x25/af_x25.c
+++ b/net/x25/af_x25.c
@@ -686,6 +686,8 @@ static int x25_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		goto out;
 	}
 
+	addr->sx25_addr.x25_addr[X25_ADDR_LEN - 1] = '\0';
+
 	/* check for the null_x25_address */
 	if (strcmp(addr->sx25_addr.x25_addr, null_x25_address.x25_addr)) {
 
@@ -779,6 +781,7 @@ static int x25_connect(struct socket *sock, struct sockaddr *uaddr,
 		goto out;
 
 	rc = -ENETUNREACH;
+	addr->sx25_addr.x25_addr[X25_ADDR_LEN - 1] = '\0';
 	rt = x25_get_route(&addr->sx25_addr);
 	if (!rt)
 		goto out;
-- 
2.28.0