netdev - [PATCH] nfc: Fix the sockaddr length sanitization in llcp_sock

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Message-Id: <20170524102620.13806-1-mjurczyk@google.com>
Date:   Wed, 24 May 2017 12:26:20 +0200
From:   Mateusz Jurczyk <mjurczyk@...gle.com>
To:     Samuel Ortiz <sameo@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, security@...nel.org
Subject: [PATCH] nfc: Fix the sockaddr length sanitization in llcp_sock_connect

Fix the sockaddr length verification in the connect() handler of NFC/LLCP
sockets, to compare against the size of the actual structure expected on
input (sockaddr_nfc_llcp) instead of its shorter version (sockaddr_nfc).

Both structures are defined in include/uapi/linux/nfc.h. The fields
specific to the _llcp extended struct are as follows:

   276		__u8 dsap; /* Destination SAP, if known */
   277		__u8 ssap; /* Source SAP to be bound to */
   278		char service_name[NFC_LLCP_MAX_SERVICE_NAME]; /* Service name URI */;
   279		size_t service_name_len;

If the caller doesn't provide a sufficiently long sockaddr buffer, these
fields remain uninitialized (and they currently originate from the stack
frame of the top-level sys_connect handler). They are then copied by
llcp_sock_connect() into internal storage (nfc_llcp_sock structure), and
could be subsequently read back through the user-mode getsockname()
function (handled by llcp_sock_getname()). This would result in the
disclosure of up to ~70 uninitialized bytes from the kernel stack to
user-mode clients capable of creating AFC_NFC sockets.

Signed-off-by: Mateusz Jurczyk <mjurczyk@...gle.com>
---
 net/nfc/llcp_sock.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c
index 2ffb18e73df6..d0d12bea65cb 100644
--- a/net/nfc/llcp_sock.c
+++ b/net/nfc/llcp_sock.c
@@ -662,8 +662,7 @@ static int llcp_sock_connect(struct socket *sock, struct sockaddr *_addr,

 	pr_debug("sock %p sk %p flags 0x%x\n", sock, sk, flags);

-	if (!addr || len < sizeof(struct sockaddr_nfc) ||
-	    addr->sa_family != AF_NFC)
+	if (!addr || len < sizeof(*addr) || addr->sa_family != AF_NFC)
 		return -EINVAL;

 	if (addr->service_name_len == 0 && addr->dsap == 0)
-- 
2.13.0.219.gdb65acc882-goog