Return-path: Received: from mail-io0-f178.google.com ([209.85.223.178]:34629 "EHLO mail-io0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935795AbdEXQ6Z (ORCPT ); Wed, 24 May 2017 12:58:25 -0400 Received: by mail-io0-f178.google.com with SMTP id k91so121550650ioi.1 for ; Wed, 24 May 2017 09:58:25 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20170524102620.13806-1-mjurczyk@google.com> References: <20170524102620.13806-1-mjurczyk@google.com> From: Kees Cook Date: Wed, 24 May 2017 09:58:23 -0700 Message-ID: (sfid-20170524_185909_375593_5233ADEE) Subject: Re: [PATCH] nfc: Fix the sockaddr length sanitization in llcp_sock_connect To: Mateusz Jurczyk Cc: Samuel Ortiz , "David S. Miller" , linux-wireless , Network Development , LKML , "security@kernel.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-wireless-owner@vger.kernel.org List-ID: On Wed, May 24, 2017 at 3:26 AM, Mateusz Jurczyk wrote: > 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 Acked-by: Kees Cook -Kees > --- > 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 > -- Kees Cook Pixel Security