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Date: Wed, 24 Oct 2012 10:32:00 -0400
From: Vlad Yasevich <vyasevich@...il.com>
To: Neil Horman <nhorman@...driver.com>
CC: linux-sctp@...r.kernel.org,
"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] Make hmac algorithm selection for cookie generation dynamic
On 10/19/2012 11:52 AM, Neil Horman wrote:
> Currently sctp allows for the optional use of md5 of sha1 hmac algorithms to
> generate cookie values when establishing new connections via two build time
> config options. Theres no real reason to make this a static selection. We can
> add a sysctl that allows for the dynamic selection of these algorithms at run
> time, with the default value determined by the corresponding crypto library
> config options. It saves us two needless configuration settings and enables the
> freedom for administrators to select which algorithm a particular system uses.
> This comes in handy when, for example running a system in FIPS mode, where use
> of md5 is disallowed, but SHA1 is permitted.
>
> Note: This new sysctl has no corresponding socket option to select the cookie
> hmac algorithm. I chose not to implement that intentionally, as RFC 6458
> contains no option for this value, and I opted not to pollute the socket option
> namespace.
>
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> CC: Vlad Yasevich <vyasevich@...il.com>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: netdev@...r.kernel.org
> ---
> Documentation/networking/ip-sysctl.txt | 14 ++++++++
> include/net/netns/sctp.h | 3 ++
> include/net/sctp/constants.h | 8 -----
> include/net/sctp/structs.h | 1 +
> net/sctp/Kconfig | 30 -----------------
> net/sctp/protocol.c | 9 ++++++
> net/sctp/socket.c | 11 ++++---
> net/sctp/sysctl.c | 59 ++++++++++++++++++++++++++++++++++
> 8 files changed, 93 insertions(+), 42 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index c7fc107..98ac0d7 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -1514,6 +1514,20 @@ cookie_preserve_enable - BOOLEAN
>
> Default: 1
>
> +cookie_hmac_alg - STRING
> + Select the hmac algorithm used when generating the cookie value sent by
> + a listening sctp socket to a connecting client in the INIT-ACK chunk.
> + Valid values are:
> + * md5
> + * sha1
> + * none
> + Ability to assign md5 or sha1 as the selected alg is predicated on the
> + configuarion of those algorithms at build time (CONFIG_CRYPTO_MD5 and
> + CONFIG_CRYPTO_SHA1).
> +
> + Default: Dependent on configuration. MD5 if available, else SHA1 if
> + available, else none.
> +
> rcvbuf_policy - INTEGER
> Determines if the receive buffer is attributed to the socket or to
> association. SCTP supports the capability to create multiple
> diff --git a/include/net/netns/sctp.h b/include/net/netns/sctp.h
> index 5e5eb1f..3573a81 100644
> --- a/include/net/netns/sctp.h
> +++ b/include/net/netns/sctp.h
> @@ -62,6 +62,9 @@ struct netns_sctp {
> /* Whether Cookie Preservative is enabled(1) or not(0) */
> int cookie_preserve_enable;
>
> + /* The namespace default hmac alg */
> + char *sctp_hmac_alg;
> +
> /* Valid.Cookie.Life - 60 seconds */
> unsigned int valid_cookie_life;
>
> diff --git a/include/net/sctp/constants.h b/include/net/sctp/constants.h
> index d053d2e..c29707d 100644
> --- a/include/net/sctp/constants.h
> +++ b/include/net/sctp/constants.h
> @@ -312,14 +312,6 @@ enum { SCTP_MAX_GABS = 16 };
> * functions simpler to write.
> */
>
> -#if defined (CONFIG_SCTP_HMAC_MD5)
> -#define SCTP_COOKIE_HMAC_ALG "hmac(md5)"
> -#elif defined (CONFIG_SCTP_HMAC_SHA1)
> -#define SCTP_COOKIE_HMAC_ALG "hmac(sha1)"
> -#else
> -#define SCTP_COOKIE_HMAC_ALG NULL
> -#endif
> -
> /* These return values describe the success or failure of a number of
> * routines which form the lower interface to SCTP_outqueue.
> */
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 0fef00f..ce5f957 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -177,6 +177,7 @@ struct sctp_sock {
>
> /* Access to HMAC transform. */
> struct crypto_hash *hmac;
> + char *sctp_hmac_alg;
>
> /* What is our base endpointer? */
> struct sctp_endpoint *ep;
> diff --git a/net/sctp/Kconfig b/net/sctp/Kconfig
> index 126b014..44ffd3e 100644
> --- a/net/sctp/Kconfig
> +++ b/net/sctp/Kconfig
> @@ -9,7 +9,6 @@ menuconfig IP_SCTP
> select CRYPTO
> select CRYPTO_HMAC
> select CRYPTO_SHA1
> - select CRYPTO_MD5 if SCTP_HMAC_MD5
> select LIBCRC32C
> ---help---
> Stream Control Transmission Protocol
> @@ -68,33 +67,4 @@ config SCTP_DBG_OBJCNT
>
> If unsure, say N
>
> -choice
> - prompt "SCTP: Cookie HMAC Algorithm"
> - default SCTP_HMAC_MD5
Did you intend to change the default algorithm to SHA1? Seems a bit
unintended and undocumented.
Would it make more sense to to change from a choice to sub-menu and
allow selection of multiple algorithms? Then use the interface you have
to change the default.
-vlad
> - help
> - HMAC algorithm to be used during association initialization. It
> - is strongly recommended to use HMAC-SHA1 or HMAC-MD5. See
> - configuration for Cryptographic API and enable those algorithms
> - to make usable by SCTP.
> -
> -config SCTP_HMAC_NONE
> - bool "None"
> - help
> - Choosing this disables the use of an HMAC during association
> - establishment. It is advised to use either HMAC-MD5 or HMAC-SHA1.
> -
> -config SCTP_HMAC_SHA1
> - bool "HMAC-SHA1"
> - help
> - Enable the use of HMAC-SHA1 during association establishment. It
> - is advised to use either HMAC-MD5 or HMAC-SHA1.
> -
> -config SCTP_HMAC_MD5
> - bool "HMAC-MD5"
> - help
> - Enable the use of HMAC-MD5 during association establishment. It is
> - advised to use either HMAC-MD5 or HMAC-SHA1.
> -
> -endchoice
> -
> endif # IP_SCTP
> diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
> index 2d51842..456bc3d 100644
> --- a/net/sctp/protocol.c
> +++ b/net/sctp/protocol.c
> @@ -1190,6 +1190,15 @@ static int sctp_net_init(struct net *net)
> /* Whether Cookie Preservative is enabled(1) or not(0) */
> net->sctp.cookie_preserve_enable = 1;
>
> + /* Default sctp sockets to use md5 as their hmac alg */
> +#if defined (CONFIG_CRYPTO_MD5)
> + net->sctp.sctp_hmac_alg = "md5";
> +#elif defined (CONFIG_CRYPTO_SHA1)
> + net->sctp.sctp_hmac_alg = "sha1";
> +#else
> + net->sctp.sctp_hmac_alg = NULL;
> +#endif
> +
> /* Max.Burst - 4 */
> net->sctp.max_burst = SCTP_DEFAULT_MAX_BURST;
>
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index d37d24f..c388262 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -109,7 +109,6 @@ static int sctp_do_bind(struct sock *, union sctp_addr *, int);
> static int sctp_autobind(struct sock *sk);
> static void sctp_sock_migrate(struct sock *, struct sock *,
> struct sctp_association *, sctp_socket_type_t);
> -static char *sctp_hmac_alg = SCTP_COOKIE_HMAC_ALG;
>
> extern struct kmem_cache *sctp_bucket_cachep;
> extern long sysctl_sctp_mem[3];
> @@ -3889,6 +3888,8 @@ SCTP_STATIC int sctp_init_sock(struct sock *sk)
> sp->default_rcv_context = 0;
> sp->max_burst = net->sctp.max_burst;
>
> + sp->sctp_hmac_alg = net->sctp.sctp_hmac_alg;
> +
> /* Initialize default setup parameters. These parameters
> * can be modified with the SCTP_INITMSG socket option or
> * overridden by the SCTP_INIT CMSG.
> @@ -5966,13 +5967,15 @@ SCTP_STATIC int sctp_listen_start(struct sock *sk, int backlog)
> struct sctp_sock *sp = sctp_sk(sk);
> struct sctp_endpoint *ep = sp->ep;
> struct crypto_hash *tfm = NULL;
> + char alg[32];
>
> /* Allocate HMAC for generating cookie. */
> - if (!sctp_sk(sk)->hmac && sctp_hmac_alg) {
> - tfm = crypto_alloc_hash(sctp_hmac_alg, 0, CRYPTO_ALG_ASYNC);
> + if (!sp->hmac && sp->sctp_hmac_alg) {
> + sprintf(alg, "hmac(%s)", sp->sctp_hmac_alg);
> + tfm = crypto_alloc_hash(alg, 0, CRYPTO_ALG_ASYNC);
> if (IS_ERR(tfm)) {
> net_info_ratelimited("failed to load transform for %s: %ld\n",
> - sctp_hmac_alg, PTR_ERR(tfm));
> + sp->sctp_hmac_alg, PTR_ERR(tfm));
> return -ENOSYS;
> }
> sctp_sk(sk)->hmac = tfm;
> diff --git a/net/sctp/sysctl.c b/net/sctp/sysctl.c
> index 70e3ba5..043889a 100644
> --- a/net/sctp/sysctl.c
> +++ b/net/sctp/sysctl.c
> @@ -62,6 +62,11 @@ extern long sysctl_sctp_mem[3];
> extern int sysctl_sctp_rmem[3];
> extern int sysctl_sctp_wmem[3];
>
> +static int proc_sctp_do_hmac_alg(ctl_table *ctl,
> + int write,
> + void __user *buffer, size_t *lenp,
> +
> + loff_t *ppos);
> static ctl_table sctp_table[] = {
> {
> .procname = "sctp_mem",
> @@ -147,6 +152,12 @@ static ctl_table sctp_net_table[] = {
> .proc_handler = proc_dointvec,
> },
> {
> + .procname = "cookie_hmac_alg",
> + .maxlen = 8,
> + .mode = 0644,
> + .proc_handler = proc_sctp_do_hmac_alg,
> + },
> + {
> .procname = "valid_cookie_life",
> .data = &init_net.sctp.valid_cookie_life,
> .maxlen = sizeof(unsigned int),
> @@ -289,6 +300,54 @@ static ctl_table sctp_net_table[] = {
> { /* sentinel */ }
> };
>
> +static int proc_sctp_do_hmac_alg(ctl_table *ctl,
> + int write,
> + void __user *buffer, size_t *lenp,
> + loff_t *ppos)
> +{
> + struct net *net = current->nsproxy->net_ns;
> + char tmp[8];
> + ctl_table tbl;
> + int ret;
> + int changed = 0;
> + char *none = "none";
> +
> + memset(&tbl, 0, sizeof(struct ctl_table));
> +
> + if (write) {
> + tbl.data = tmp;
> + tbl.maxlen = 8;
> + } else {
> + tbl.data = net->sctp.sctp_hmac_alg ? : none;
> + tbl.maxlen = strlen(tbl.data);
> + }
> + ret = proc_dostring(&tbl, write, buffer, lenp, ppos);
> +
> + if (write) {
> +#ifdef CONFIG_CRYPTO_MD5
> + if (!strncmp(tmp, "md5", 3)) {
> + net->sctp.sctp_hmac_alg = "md5";
> + changed = 1;
> + }
> +#endif
> +#ifdef CONFIG_CRYPTO_SHA1
> + if (!strncmp(tmp, "sha1", 4)) {
> + net->sctp.sctp_hmac_alg = "sha1";
> + changed = 1;
> + }
> +#endif
> + if (!strncmp(tmp, "none", 4)) {
> + net->sctp.sctp_hmac_alg = NULL;
> + changed = 1;
> + }
> +
> + if (!changed)
> + ret = -EINVAL;
> + }
> +
> + return ret;
> +}
> +
> int sctp_sysctl_net_register(struct net *net)
> {
> struct ctl_table *table;
>
--
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