The xt_SYSRQ hash now includes the destination IPv4 or IPv6 address
which makes it harder to replay a request to many different machines
in the hope that some of them are using the same password.
---
extensions/libxt_SYSRQ.man | 17 +++++++++++------
extensions/xt_SYSRQ.c | 13 +++++++++----
2 files changed, 20 insertions(+), 10 deletions(-)
diff --git a/extensions/libxt_SYSRQ.man b/extensions/libxt_SYSRQ.man
index 89878e0..5470066 100644
--- a/extensions/libxt_SYSRQ.man
+++ b/extensions/libxt_SYSRQ.man
@@ -36,6 +36,8 @@ The SYSRQ password can be changed through
.IP
echo \-n "password" >/sys/module/xt_SYSRQ/parameters/password
.PP
+The module will not respond to sysrq requests until a password has been set.
+.PP
Alternatively, the password may be specified at modprobe time, but this is
insecure as people can possible see it through ps(1). You can use an option
line in e.g. /etc/modprobe.d/xt_sysrq if it is properly guarded, that is, only
@@ -60,12 +62,13 @@ password="password"
seqno="$(date +%s)"
salt="$(dd bs=12 count=1 if=/dev/urandom 2>/dev/null |
openssl enc \-base64)"
+ipaddr=10.10.25.7
req="$sysrq_key,$seqno,$salt"
-req="$req,$(echo \-n "$req,$password" | sha1sum | cut \-c1\-40)"
+req="$req,$(echo \-n "$req,$ipaddr,$password" | sha1sum | cut \-c1\-40)"
-echo "$req" | socat stdin udp\-sendto:10.10.25.7:9
+echo "$req" | socat stdin udp\-sendto:$ipaddr:9
# or
-echo "$req" | netcat \-uw1 10.10.25.7 9
+echo "$req" | netcat \-uw1 $ipaddr 9
.fi
.PP
See the Linux docs for possible sysrq keys. Important ones are: re(b)oot,
@@ -73,8 +76,10 @@ power(o)ff, (s)ync filesystems, (u)mount and remount readonly. More than one
sysrq key can be used at once, but bear in mind that, for example, a sync may
not complete before a subsequent reboot or poweroff.
.PP
+An IPv4 address should have no leading zeros, an IPv6 address should
+be in the form recommended by RFC 5952. The debug option will log the
+correct form of the address.
+.PP
The hashing scheme should be enough to prevent mis-use of SYSRQ in many
environments, but it is not perfect: take reasonable precautions to
-protect your machines. Most importantly ensure that each machine has a
-different password; there is scant protection for a SYSRQ packet being
-applied to a machine that happens to have the same password.
+protect your machines.
diff --git a/extensions/xt_SYSRQ.c b/extensions/xt_SYSRQ.c
index 723e813..1befcdf 100644
--- a/extensions/xt_SYSRQ.c
+++ b/extensions/xt_SYSRQ.c
@@ -4,6 +4,8 @@
*
* Based upon the ipt_SYSRQ idea by Marek Zalem <marek [at] terminus sk>
*
+ * Security additions John Haxby <john.haxby [at] oracle com>
+ *
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* version 2 or 3 as published by the Free Software Foundation.
@@ -58,13 +60,13 @@ static char *sysrq_hexdigest;
* is a series of sysrq requests; <seqno> is a sequence number that must be
* greater than the last sequence number; <salt> is some random bytes; and
* <hash> is the hash of everything up to and including the preceding ","
- * together with the password.
+ * together with "<dstaddr>,<password>".
*
* For example
*
* salt=$RANDOM
* req="s,$(date +%s),$salt"
- * echo "$req,$(echo -n $req,secret | sha1sum | cut -c1-40)"
+ * echo "$req,$(echo -n $req,10.10.25.1,secret | sha1sum | cut -c1-40)"
*
* You will want a better salt and password than that though :-)
*/
@@ -121,7 +123,6 @@ static unsigned int sysrq_tg(const void *pdata, uint16_t len)
sg_init_table(sg, 2);
#endif
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);
@@ -223,6 +224,7 @@ sysrq_tg4(struct sk_buff **pskb, const struct xt_action_param *par)
": %pI4:%u -> %pI4:%u len=%u\n",
&iph->saddr, htons(udph->source),
&iph->daddr, htons(udph->dest), len);
+ sprintf(sysrq_digest_password, "%pI4,%s", &iph->daddr, sysrq_password);
return sysrq_tg((void *)udph + sizeof(struct udphdr), len);
}
@@ -253,6 +255,7 @@ sysrq_tg6(struct sk_buff **pskb, const struct xt_action_param *par)
": [%pI6c]:%hu -> [%pI6c]:%hu len=%u\n",
&iph->saddr, ntohs(udph->source),
&iph->daddr, ntohs(udph->dest), len);
+ sprintf(sysrq_digest_password, "%pI6c,%s", &iph->daddr, sysrq_password);
return sysrq_tg((void *)udph + sizeof(struct udphdr), len);
}
#endif
@@ -340,7 +343,9 @@ static int __init sysrq_crypto_init(void)
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);
+ sysrq_digest_password =
+ kmalloc(sizeof("xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:255.255.255.255") +
+ sizeof(sysrq_password), GFP_KERNEL);
if (sysrq_digest_password == NULL)
goto fail;
do_gettimeofday(&now);
--
1.7.5.4
--
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