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netfilter-devel: [PATCH 1/2] netfilter: xtables: inclusion of xt

[PATCH 1/2] netfilter: xtables: inclusion of xt_SYSRQ

From: Jan Engelhardt <jengelh_at_nospam>
Date: Wed Apr 21 2010 - 10:26:56 GMT
To: kaber@trash.net

The SYSRQ target will allow to remotely invoke sysrq on the local
machine. Authentication is by means of a pre-shared key that can
either be transmitted plaintext or digest-secured.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
--- net/netfilter/Kconfig | 12 ++ net/netfilter/Makefile | 1 + net/netfilter/xt_SYSRQ.c | 354 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 367 insertions(+), 0 deletions(-) create mode 100644 net/netfilter/xt_SYSRQ.c diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig index 673a6c8..bfd9b6f 100644 --- a/net/netfilter/Kconfig +++ b/net/netfilter/Kconfig @@ -502,6 +502,18 @@ config NETFILTER_XT_TARGET_RATEEST To compile it as a module, choose M here. If unsure, say N. +config NETFILTER_XT_TARGET_SYSRQ + tristate '"SYSRQ" - remote sysrq invocation' + depends on NETFILTER_ADVANCED + ---help--- + This option enables the "SYSRQ" target which can be used to trigger + sysrq from a remote machine using a magic UDP packet with a pre-shared + password. This is useful when the receiving host has locked up in an + Oops yet still can process incoming packets. + + Besides plaintext packets, digest-secured SYSRQ requests will be + supported when CONFIG_CRYPTO is enabled. + config NETFILTER_XT_TARGET_TEE tristate '"TEE" - packet cloning to alternate destiantion' depends on NETFILTER_ADVANCED diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile index 14e3a8f..f032195 100644 --- a/net/netfilter/Makefile +++ b/net/netfilter/Makefile @@ -56,6 +56,7 @@ obj-$(CONFIG_NETFILTER_XT_TARGET_NFQUEUE) += xt_NFQUEUE.o obj-$(CONFIG_NETFILTER_XT_TARGET_NOTRACK) += xt_NOTRACK.o obj-$(CONFIG_NETFILTER_XT_TARGET_RATEEST) += xt_RATEEST.o obj-$(CONFIG_NETFILTER_XT_TARGET_SECMARK) += xt_SECMARK.o +obj-$(CONFIG_NETFILTER_XT_TARGET_SYSRQ) += xt_SYSRQ.o obj-$(CONFIG_NETFILTER_XT_TARGET_TPROXY) += xt_TPROXY.o obj-$(CONFIG_NETFILTER_XT_TARGET_TCPMSS) += xt_TCPMSS.o obj-$(CONFIG_NETFILTER_XT_TARGET_TCPOPTSTRIP) += xt_TCPOPTSTRIP.o diff --git a/net/netfilter/xt_SYSRQ.c b/net/netfilter/xt_SYSRQ.c new file mode 100644 index 0000000..929b204 --- /dev/null +++ b/net/netfilter/xt_SYSRQ.c @@ -0,0 +1,354 @@ +/* + * "SYSRQ" target extension for Netfilter + * Copyright © Jan Engelhardt <jengelh [at] medozas de>, 2008 - 2010 + * + * Based upon the ipt_SYSRQ idea by Marek Zalem <marek [at] terminus sk> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * version 2 or later as published by the Free Software Foundation. + */ +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt +#include <linux/in.h> +#include <linux/ip.h> +#include <linux/ipv6.h> +#include <linux/module.h> +#include <linux/skbuff.h> +#include <linux/sysrq.h> +#include <linux/udp.h> +#include <linux/netfilter_ipv4/ip_tables.h> +#include <linux/netfilter_ipv6/ip6_tables.h> +#include <linux/netfilter/x_tables.h> +#include <linux/crypto.h> +#include <linux/scatterlist.h> +#include <net/ip.h> + +#if defined(CONFIG_CRYPTO) || defined(CRYPTO_CONFIG_MODULE) +# define WITH_CRYPTO 1 +#endif +#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE) +# define WITH_IPV6 1 +#endif + +static bool sysrq_once; +static char sysrq_password[64]; +static char sysrq_hash[16] = "sha1"; +static long sysrq_seqno; +static int sysrq_debug; +module_param_string(password, sysrq_password, sizeof(sysrq_password), + S_IRUSR | S_IWUSR); +module_param_string(hash, sysrq_hash, sizeof(sysrq_hash), S_IRUSR); +module_param_named(seqno, sysrq_seqno, long, S_IRUSR | S_IWUSR); +module_param_named(debug, sysrq_debug, int, S_IRUSR | S_IWUSR); +MODULE_PARM_DESC(password, "password for remote sysrq"); +MODULE_PARM_DESC(hash, "hash algorithm, default sha1"); +MODULE_PARM_DESC(seqno, "sequence number for remote sysrq"); +MODULE_PARM_DESC(debug, "debugging: 0=off, 1=on"); + +#ifdef WITH_CRYPTO +static struct crypto_hash *sysrq_tfm; +static int sysrq_digest_size; +static unsigned char *sysrq_digest_password; +static unsigned char *sysrq_digest; +static char *sysrq_hexdigest; + +/* + * The data is of the form "<requests>,<seqno>,<salt>,<hash>" where <requests> + * is a series of sysrq requests; <seqno> is a sequence number that must be + * greater than the last sequence number; <salt> is some random bytes; and + * <hash> is the hash of everything up to and including the preceding "," + * together with the password. + * + * For example + * + * salt=$RANDOM + * req="s,$(date +%s),$salt" + * echo "$req,$(echo -n $req,secret | sha1sum | cut -c1-40)" + * + * You will want a better salt and password than that though :-) + */ +static unsigned int sysrq_tg(const void *pdata, uint16_t len) +{ + const char *data = pdata; + int i, n; + struct scatterlist sg[2]; + struct hash_desc desc; + int ret; + long new_seqno = 0; + + if (*sysrq_password == '\0') { + if (!sysrq_once) + pr_info("No password set\n"); + sysrq_once = true; + return NF_DROP; + } + if (len == 0) + return NF_DROP; + + for (i = 0; sysrq_password[i] != '\0' && + sysrq_password[i] != '\n'; ++i) + /* loop */; + sysrq_password[i] = '\0'; + + i = 0; + for (n = 0; n < len - 1; ++n) { + if (i == 1 && '0' <= data[n] && data[n] <= '9') + new_seqno = 10L * new_seqno + data[n] - '0'; + if (data[n] == ',' && ++i == 3) + break; + } + ++n; + if (i != 3) { + if (sysrq_debug) + pr_info("badly formatted request\n"); + return NF_DROP; + } + if (sysrq_seqno >= new_seqno) { + if (sysrq_debug) + pr_info("old sequence number ignored\n"); + return NF_DROP; + } + + desc.tfm = sysrq_tfm; + desc.flags = 0; + ret = crypto_hash_init(&desc); + if (ret != 0) + goto hash_fail; + sg_init_table(sg, 2); + sg_set_buf(&sg[0], data, n); + strcpy(sysrq_digest_password, sysrq_password); + i = strlen(sysrq_digest_password); + sg_set_buf(&sg[1], sysrq_digest_password, i); + ret = crypto_hash_digest(&desc, sg, n + i, sysrq_digest); + if (ret != 0) + goto hash_fail; + + for (i = 0; i < sysrq_digest_size; ++i) { + sysrq_hexdigest[2*i] = + "0123456789abcdef"[(sysrq_digest[i] >> 4) & 0xf]; + sysrq_hexdigest[2*i+1] = + "0123456789abcdef"[sysrq_digest[i] & 0xf]; + } + sysrq_hexdigest[2*sysrq_digest_size] = '\0'; + if (len - n < sysrq_digest_size) { + if (sysrq_debug) + pr_info("Short digest, expected %s\n", + sysrq_hexdigest); + return NF_DROP; + } + if (strncmp(data + n, sysrq_hexdigest, sysrq_digest_size) != 0) { + if (sysrq_debug) + pr_info("Bad digest, expected %s\n", sysrq_hexdigest); + return NF_DROP; + } + + /* Now we trust the requester */ + sysrq_seqno = new_seqno; + for (i = 0; i < len && data[i] != ','; ++i) { + pr_info("SysRq %c\n", data[i]); + handle_sysrq(data[i], NULL); + } + return NF_ACCEPT; + + hash_fail: + pr_warning("digest failure\n"); + return NF_DROP; +} +#else +static unsigned int sysrq_tg(const void *pdata, uint16_t len) +{ + const char *data = pdata; + char c; + + if (*sysrq_password == '\0') { + if (!sysrq_once) + pr_info("No password set\n"); + sysrq_once = true; + return NF_DROP; + } + + if (len == 0) + return NF_DROP; + + c = *data; + if (strncmp(&data[1], sysrq_password, len - 1) != 0) { + pr_warning("Failed attempt - password mismatch\n"); + return NF_DROP; + } + + handle_sysrq(c, NULL); + return NF_ACCEPT; +} +#endif + +static unsigned int +sysrq_tg4(struct sk_buff *skb, const struct xt_target_param *par) +{ + const struct iphdr *iph; + const struct udphdr *udph; + uint16_t len; + + if (skb_linearize(skb) < 0) + return NF_DROP; + + iph = ip_hdr(skb); + if (iph->protocol != IPPROTO_UDP && iph->protocol != IPPROTO_UDPLITE) + return NF_DROP; + + udph = (const void *)iph + ip_hdrlen(skb); + len = ntohs(udph->len) - sizeof(struct udphdr); + + if (sysrq_debug) + pr_info(": %pI4:%u -> :%u len=%u\n", &iph->saddr, + htons(udph->source), htons(udph->dest), len); + return sysrq_tg((void *)udph + sizeof(struct udphdr), len); +} + +#ifdef WITH_IPV6 +static unsigned int +sysrq_tg6(struct sk_buff *skb, const struct xt_target_param *par) +{ + const struct ipv6hdr *iph; + const struct udphdr *udph; + unsigned short frag_off; + unsigned int th_off; + uint16_t len; + + if (skb_linearize(skb) < 0) + return NF_DROP; + + iph = ipv6_hdr(skb); + if (ipv6_find_hdr(skb, &th_off, IPPROTO_UDP, &frag_off) < 0 || + frag_off > 0) + return NF_ACCEPT; /* sink it */ + + udph = (const void *)iph + th_off; + len = ntohs(udph->len) - sizeof(struct udphdr); + + if (sysrq_debug) + pr_info("%pI6:%hu -> :%hu len=%u\n", &iph->saddr, + ntohs(udph->source), ntohs(udph->dest), len); + return sysrq_tg(udph + sizeof(struct udphdr), len); +} +#endif + +static int sysrq_tg_check(const struct xt_tgchk_param *par) +{ + if (par->target->family == NFPROTO_IPV4) { + const struct ipt_entry *entry = par->entryinfo; + + if ((entry->ip.proto != IPPROTO_UDP && + entry->ip.proto != IPPROTO_UDPLITE) || + entry->ip.invflags & XT_INV_PROTO) + goto out; + } else if (par->target->family == NFPROTO_IPV6) { + const struct ip6t_entry *entry = par->entryinfo; + + if ((entry->ipv6.proto != IPPROTO_UDP && + entry->ipv6.proto != IPPROTO_UDPLITE) || + entry->ipv6.invflags & XT_INV_PROTO) + goto out; + } + + return true; + + out: + pr_info("only available for UDP and UDP-Lite"); + return false; +} + +static struct xt_target sysrq_tg_reg[] __read_mostly = { + { + .name = "SYSRQ", + .revision = 1, + .family = NFPROTO_IPV4, + .target = sysrq_tg4, + .checkentry = sysrq_tg_check, + .me = THIS_MODULE, + }, +#ifdef WITH_IPV6 + { + .name = "SYSRQ", + .revision = 1, + .family = NFPROTO_IPV6, + .target = sysrq_tg6, + .checkentry = sysrq_tg_check, + .me = THIS_MODULE, + }, +#endif +}; + +static void sysrq_crypto_exit(void) +{ +#ifdef WITH_CRYPTO + if (sysrq_tfm) + crypto_free_hash(sysrq_tfm); + if (sysrq_digest) + kfree(sysrq_digest); + if (sysrq_hexdigest) + kfree(sysrq_hexdigest); + if (sysrq_digest_password) + kfree(sysrq_digest_password); +#endif +} + +static int __init sysrq_crypto_init(void) +{ +#if defined(WITH_CRYPTO) + struct timeval now; + int ret; + + sysrq_tfm = crypto_alloc_hash(sysrq_hash, 0, CRYPTO_ALG_ASYNC); + if (IS_ERR(sysrq_tfm)) { + pr_err("Could not find or load %s hash\n", sysrq_hash); + sysrq_tfm = NULL; + ret = PTR_ERR(sysrq_tfm); + goto fail; + } + sysrq_digest_size = crypto_hash_digestsize(sysrq_tfm); + sysrq_digest = kmalloc(sysrq_digest_size, GFP_KERNEL); + ret = -ENOMEM; + if (sysrq_digest == NULL) + goto fail; + sysrq_hexdigest = kmalloc(2 * sysrq_digest_size + 1, GFP_KERNEL); + if (sysrq_hexdigest == NULL) + goto fail; + sysrq_digest_password = kmalloc(sizeof(sysrq_password), GFP_KERNEL); + if (sysrq_digest_password == NULL) + goto fail; + do_gettimeofday(&now); + sysrq_seqno = now.tv_sec; + ret = xt_register_targets(sysrq_tg_reg, ARRAY_SIZE(sysrq_tg_reg)); + if (ret < 0) + goto fail; + return ret; + + fail: + sysrq_crypto_exit(); + return ret; +#else + pr_info("compiled without crypto\n"); +#endif + return -EINVAL; +} + +static int __init sysrq_tg_init(void) +{ + if (sysrq_crypto_init() < 0) + pr_info("starting without crypto\n"); + return xt_register_targets(sysrq_tg_reg, ARRAY_SIZE(sysrq_tg_reg)); +} + +static void __exit sysrq_tg_exit(void) +{ + sysrq_crypto_exit(); + xt_unregister_targets(sysrq_tg_reg, ARRAY_SIZE(sysrq_tg_reg)); +} + +module_init(sysrq_tg_init); +module_exit(sysrq_tg_exit); +MODULE_DESCRIPTION("Xtables: triggering SYSRQ remotely"); +MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>"); +MODULE_LICENSE("GPL"); +MODULE_ALIAS("ipt_SYSRQ"); +MODULE_ALIAS("ip6t_SYSRQ"); -- 1.7.0.5 -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html