@@ -25,6 +25,7 @@ Description:
lsm: [[subj_user=] [subj_role=] [subj_type=]
[obj_user=] [obj_role=] [obj_type=]]
option: [[appraise_type=]] [template=] [permit_directio]
+ [appraise_flag=]
base: func:= [BPRM_CHECK][MMAP_CHECK][CREDS_CHECK][FILE_CHECK][MODULE_CHECK]
[FIRMWARE_CHECK]
[KEXEC_KERNEL_CHECK] [KEXEC_INITRAMFS_CHECK]
@@ -38,6 +39,9 @@ Description:
fowner:= decimal value
lsm: are LSM specific
option: appraise_type:= [imasig] [imasig|modsig]
+ appraise_flag:= [check_blacklist]
+ Currently, blacklist check is only for files signed with appended
+ signature.
template:= name of a defined IMA template type
(eg, ima-ng). Only valid when action is "measure".
pcr:= decimal value
@@ -256,6 +256,8 @@ int ima_policy_show(struct seq_file *m, void *v);
#define IMA_APPRAISE_KEXEC 0x40
#ifdef CONFIG_IMA_APPRAISE
+int ima_check_blacklist(struct integrity_iint_cache *iint,
+ const struct modsig *modsig, int pcr);
int ima_appraise_measurement(enum ima_hooks func,
struct integrity_iint_cache *iint,
struct file *file, const unsigned char *filename,
@@ -271,6 +273,12 @@ int ima_read_xattr(struct dentry *dentry,
struct evm_ima_xattr_data **xattr_value);
#else
+static inline int ima_check_blacklist(struct integrity_iint_cache *iint,
+ const struct modsig *modsig, int pcr)
+{
+ return 0;
+}
+
static inline int ima_appraise_measurement(enum ima_hooks func,
struct integrity_iint_cache *iint,
struct file *file,
@@ -12,6 +12,7 @@
#include <linux/magic.h>
#include <linux/ima.h>
#include <linux/evm.h>
+#include <keys/system_keyring.h>
#include "ima.h"
@@ -303,6 +304,38 @@ static int modsig_verify(enum ima_hooks func, const struct modsig *modsig,
return rc;
}
+/*
+ * ima_check_blacklist - determine if the binary is blacklisted.
+ *
+ * Add the hash of the blacklisted binary to the measurement list, based
+ * on policy.
+ *
+ * Returns -EPERM if the hash is blacklisted.
+ */
+int ima_check_blacklist(struct integrity_iint_cache *iint,
+ const struct modsig *modsig, int pcr)
+{
+ enum hash_algo hash_algo;
+ const u8 *digest = NULL;
+ u32 digestsize = 0;
+ int rc = 0;
+
+ if (!(iint->flags & IMA_CHECK_BLACKLIST))
+ return 0;
+
+ if (iint->flags & IMA_MODSIG_ALLOWED && modsig) {
+ ima_get_modsig_digest(modsig, &hash_algo, &digest, &digestsize);
+
+ rc = is_binary_blacklisted(digest, digestsize);
+ if ((rc == -EPERM) && (iint->flags & IMA_MEASURE))
+ process_buffer_measurement(digest, digestsize,
+ "blacklisted-hash", NONE,
+ pcr);
+ }
+
+ return rc;
+}
+
/*
* ima_appraise_measurement - appraise file measurement
*
@@ -335,10 +335,14 @@ static int process_measurement(struct file *file, const struct cred *cred,
xattr_value, xattr_len, modsig, pcr,
template_desc);
if (rc == 0 && (action & IMA_APPRAISE_SUBMASK)) {
- inode_lock(inode);
- rc = ima_appraise_measurement(func, iint, file, pathname,
- xattr_value, xattr_len, modsig);
- inode_unlock(inode);
+ rc = ima_check_blacklist(iint, modsig, pcr);
+ if (rc != -EPERM) {
+ inode_lock(inode);
+ rc = ima_appraise_measurement(func, iint, file,
+ pathname, xattr_value,
+ xattr_len, modsig);
+ inode_unlock(inode);
+ }
if (!rc)
rc = mmap_violation_check(func, file, &pathbuf,
&pathname, filename);
@@ -765,8 +765,8 @@ enum {
Opt_fsuuid, Opt_uid_eq, Opt_euid_eq, Opt_fowner_eq,
Opt_uid_gt, Opt_euid_gt, Opt_fowner_gt,
Opt_uid_lt, Opt_euid_lt, Opt_fowner_lt,
- Opt_appraise_type, Opt_permit_directio,
- Opt_pcr, Opt_template, Opt_err
+ Opt_appraise_type, Opt_appraise_flag,
+ Opt_permit_directio, Opt_pcr, Opt_template, Opt_err
};
static const match_table_t policy_tokens = {
@@ -798,6 +798,7 @@ static const match_table_t policy_tokens = {
{Opt_euid_lt, "euid<%s"},
{Opt_fowner_lt, "fowner<%s"},
{Opt_appraise_type, "appraise_type=%s"},
+ {Opt_appraise_flag, "appraise_flag=%s"},
{Opt_permit_directio, "permit_directio"},
{Opt_pcr, "pcr=%s"},
{Opt_template, "template=%s"},
@@ -1172,6 +1173,11 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry)
else
result = -EINVAL;
break;
+ case Opt_appraise_flag:
+ ima_log_string(ab, "appraise_flag", args[0].from);
+ if (strstr(args[0].from, "blacklist"))
+ entry->flags |= IMA_CHECK_BLACKLIST;
+ break;
case Opt_permit_directio:
entry->flags |= IMA_PERMIT_DIRECTIO;
break;
@@ -1500,6 +1506,8 @@ int ima_policy_show(struct seq_file *m, void *v)
else
seq_puts(m, "appraise_type=imasig ");
}
+ if (entry->flags & IMA_CHECK_BLACKLIST)
+ seq_puts(m, "appraise_flag=check_blacklist ");
if (entry->flags & IMA_PERMIT_DIRECTIO)
seq_puts(m, "permit_directio ");
rcu_read_unlock();
@@ -32,6 +32,7 @@
#define EVM_IMMUTABLE_DIGSIG 0x08000000
#define IMA_FAIL_UNVERIFIABLE_SIGS 0x10000000
#define IMA_MODSIG_ALLOWED 0x20000000
+#define IMA_CHECK_BLACKLIST 0x40000000
#define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \
IMA_HASH | IMA_APPRAISE_SUBMASK)
Asymmetric private keys are used to sign multiple files. The kernel currently support checking against blacklisted keys. However, if the public key is blacklisted, any file signed by the blacklisted key will automatically fail signature verification. We might not want to blacklist all the files signed by a particular key, but just a single file. Blacklisting the public key is not fine enough granularity. This patch adds support for checking against the blacklisted hash of the file based on the IMA policy. The blacklisted hash is the file hash without the appended signature. Defined is a new policy option "appraise_flag=check_blacklist". In addition to the blacklisted binary hashes stored in the firmware "dbx" variable, the Linux kernel may be configured to load blacklisted binary hashes onto the .blacklist keyring as well. The following example shows how to blacklist a kernel module. $ sha256sum kernel/kheaders.ko 77fa889b35a05338ec52e51591c1b89d4c8d1c99a21251d7c22b1a8642a6bad3 kern el/kheaders.ko $ grep BLACKLIST .config # CONFIG_IMA_BLACKLIST_KEYRING is not set CONFIG_SYSTEM_BLACKLIST_KEYRING=y CONFIG_SYSTEM_BLACKLIST_HASH_LIST="blacklist-hash-list" $ cat certs/blacklist-hash-list "bin:77fa889b35a05338ec52e51591c1b89d4c8d1c99a21251d7c22b1a8642a6bad3" Update the IMA custom measurement and appraisal policy rules (/etc/ima-policy): measure func=MODULE_CHECK template=ima-modsig appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig After building, installing, and rebooting the kernel: # keyctl show %keyring:.blacklist | grep 77fa889b35a05 545660333 ---lswrv 0 0 \_ blacklist: bin:77fa889b35a05338ec52e51591c1b89d4c8d1c99a21251d7c22b1a8642a6bad3 # cat /sys/kernel/security/ima/policy | grep MODULE_CHECK measure func=MODULE_CHECK template=ima-modsig appraise func=MODULE_CHECK appraise_flag=check_blacklist appraise_type=imasig|modsig # modprobe kheaders modprobe: ERROR: could not insert 'kheaders': Permission denied # cat /sys/kernel/security/ima/ascii_runtime_measurements 10 0c9834db5a0182c1fb0cdc5d3adcf11a11fd83dd ima-sig sha256:3bc6ed4f0b4d6e31bc1dbc9ef844605abc7afdc6d81a57d77a1ec9407997c40 2 /usr/lib/modules/5.4.0-rc3+/kernel/kernel/kheaders.ko 10 82aad2bcc3fa8ed94762356b5c14838f3bcfa6a0 ima-modsig sha256:3bc6ed4f0b4d6e31bc1dbc9ef844605abc7afdc6d81a57d77a1ec9407997c40 2 /usr/lib/modules/5.4.0rc3+/kernel/kernel/kheaders.ko sha256:77fa889b3 5a05338ec52e51591c1b89d4c8d1c99a21251d7c22b1a8642a6bad3 3082029a06092a864886f70d010702a082028b30820287020101310d300b0609608648 016503040201300b06092a864886f70d01070131820264.... 10 25b72217cc1152b44b134ce2cd68f12dfb71acb3 ima-buf sha256:8b58427fedcf8f4b20bc8dc007f2e232bf7285d7b93a66476321f9c2a3aa132 b blacklisted-hash 77fa889b35a05338ec52e51591c1b89d4c8d1c99a21251d7c22b1a8642a6bad3 Signed-off-by: Nayna Jain <nayna@linux.ibm.com> --- Documentation/ABI/testing/ima_policy | 4 ++++ security/integrity/ima/ima.h | 8 +++++++ security/integrity/ima/ima_appraise.c | 33 +++++++++++++++++++++++++++ security/integrity/ima/ima_main.c | 12 ++++++---- security/integrity/ima/ima_policy.c | 12 ++++++++-- security/integrity/integrity.h | 1 + 6 files changed, 64 insertions(+), 6 deletions(-)