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@xxxxxxxxxx>
---
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@xxxxxxxxxx>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("ipt_SYSRQ");
+MODULE_ALIAS("ip6t_SYSRQ");
--
1.7.0.5
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