@@ -20,11 +20,15 @@
#include <linux/rcupdate.h>
#include <linux/parser.h>
#include <linux/vmalloc.h>
+#include <linux/verification.h>
#include "ima.h"
static DEFINE_MUTEX(ima_write_mutex);
+/* maximum length of token allowed for signed appraise mode */
+#define APPRAISE_MAX_TOKEN_SIZE (512 * 1024)
+
bool ima_canonical_fmt;
static int __init default_canonical_fmt_setup(char *str)
{
@@ -466,8 +470,112 @@ static ssize_t ima_appraise_mode_read(struct file *filp,
return simple_read_from_buffer(buf, count, ppos, mode, strlen(mode));
}
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+
+static int check_signature_info(char *buf, size_t count)
+{
+ u8 *p;
+
+ /*
+ * In order to tune the appraise mode, a PKCS#7 signature is
+ * supplied.
+ *
+ * Assuming ASN.1 encoding supplied, the minimal length would be
+ * 4-byte header plus at least 256-byte payload.
+ */
+ if (count < 260)
+ return -EINVAL;
+
+ p = (u8 *)buf;
+
+ /* The primitive type must be a sequence */
+ if (p[0] != 0x30 || p[1] != 0x82)
+ return -EINVAL;
+
+ /* Match up the length of the supplied buffer */
+ if (be16_to_cpup((__be16 *)(p + 2)) != count - 4)
+ return -EINVAL;
+
+ return 0;
+}
+
+/* Verify the supplied PKCS#7 signature. The signed content may be off,
+ * enforce, log, fix.
+ */
+static int repopulate_ima_appraise_mode(void *pkcs7, size_t pkcs7_len)
+{
+ static char *appraise_mode_strings[] = { "off", "enforce", "fix", "log" };
+ static int appraise_modes[] = {
+ 0,
+ IMA_APPRAISE_ENFORCE,
+ IMA_APPRAISE_FIX,
+ IMA_APPRAISE_LOG,
+ };
+ int index, ret = -1;
+ const char *s;
+ int size = ARRAY_SIZE(appraise_mode_strings);
+
+ for (index = 0; index < size; index++) {
+ s = appraise_mode_strings[index];
+ ret = verify_pkcs7_signature(s, strlen(s), pkcs7, pkcs7_len,
+ NULL, VERIFYING_UNSPECIFIED_SIGNATURE,
+ NULL, NULL);
+ if (!ret)
+ break;
+ }
+
+ if (index == size)
+ goto out;
+
+ ima_appraise = appraise_modes[index];
+
+out:
+ return ret;
+}
+
+static ssize_t ima_appraise_mode_write(struct file *filp,
+ const char __user *ubuf,
+ size_t count, loff_t *ppos)
+{
+ char *buf;
+ ssize_t ret;
+
+ if (*ppos > 1)
+ return -EFBIG;
+
+ if (count > APPRAISE_MAX_TOKEN_SIZE)
+ return -EFBIG;
+
+ buf = kmalloc(count, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+
+ ret = simple_write_to_buffer(buf, count, ppos, ubuf, count);
+ if (ret <= 0)
+ goto out;
+
+ ret = check_signature_info(buf, count);
+ if (ret)
+ goto out;
+
+ ret = repopulate_ima_appraise_mode(buf, count);
+ if (ret)
+ goto out;
+
+ ret = count;
+
+out:
+ kfree(buf);
+ return ret;
+}
+
+#endif
+
static const struct file_operations ima_appraise_mode_ops = {
.read = ima_appraise_mode_read,
+#ifdef CONFIG_SYSTEM_DATA_VERIFICATION
+ .write = ima_appraise_mode_write,
+#endif
.llseek = generic_file_llseek,
};
In order to tune appraise mode in runtime, writing a PKCS#7 signature corresponding the signed content is required. The content should be off, enforce, log or fix. Given a simple way to archive this: $ echo -n off > mode $ openssl smime -sign -nocerts -noattr -binary \ -in mode -inkey <system_trusted_key> \ -signer <cert> -outform der -out mode.p7s $ sudo cat mode.p7s \ > /sys/kernel/security/ima/appraise_mode Note that the signing key must be a trust key located in system trusted keyring. So even the root privilege cannot simply disable the enforcement. Signed-off-by: luanshi <zhangliguang@linux.alibaba.com> Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com> --- security/integrity/ima/ima_fs.c | 108 ++++++++++++++++++++++++++++++++ 1 file changed, 108 insertions(+)