From ae1ba1676b88e6c62368a433c7e2d0417e9879fd Mon Sep 17 00:00:00 2001 From: Matthew Garrett Date: Tue, 7 Nov 2017 07:18:35 -0800 Subject: EVM: Allow userland to permit modification of EVM-protected metadata When EVM is enabled it forbids modification of metadata protected by EVM unless there is already a valid EVM signature. If any modification is made, the kernel will then generate a new EVM HMAC. However, this does not map well on use cases which use only asymmetric EVM signatures, as in this scenario the kernel is unable to generate new signatures. This patch extends the /sys/kernel/security/evm interface to allow userland to request that modification of these xattrs be permitted. This is only permitted if no keys have already been loaded. In this configuration, modifying the metadata will invalidate the EVM appraisal on the file in question. This allows packaging systems to write out new files, set the relevant extended attributes and then move them into place. There's also some refactoring of the use of evm_initialized in order to avoid heading down codepaths that assume there's a key available. Signed-off-by: Matthew Garrett Signed-off-by: Mimi Zohar --- Documentation/ABI/testing/evm | 54 ++++++++++++++++++++++++++++--------------- 1 file changed, 35 insertions(+), 19 deletions(-) (limited to 'Documentation/ABI') diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm index 9578247e1792..d12cb2eae9ee 100644 --- a/Documentation/ABI/testing/evm +++ b/Documentation/ABI/testing/evm @@ -14,30 +14,46 @@ Description: generated either locally or remotely using an asymmetric key. These keys are loaded onto root's keyring using keyctl, and EVM is then enabled by - echoing a value to /evm: + echoing a value to /evm made up of the + following bits: - 1: enable HMAC validation and creation - 2: enable digital signature validation - 3: enable HMAC and digital signature validation and HMAC - creation + Bit Effect + 0 Enable HMAC validation and creation + 1 Enable digital signature validation + 2 Permit modification of EVM-protected metadata at + runtime. Not supported if HMAC validation and + creation is enabled. + 31 Disable further runtime modification of EVM policy - Further writes will be blocked if HMAC support is enabled or - if bit 32 is set: + For example: - echo 0x80000002 >/evm + echo 1 >/evm - will enable digital signature validation and block - further writes to /evm. + will enable HMAC validation and creation - Until this is done, EVM can not create or validate the - 'security.evm' xattr, but returns INTEGRITY_UNKNOWN. - Loading keys and signaling EVM should be done as early - as possible. Normally this is done in the initramfs, - which has already been measured as part of the trusted - boot. For more information on creating and loading - existing trusted/encrypted keys, refer to: + echo 0x80000003 >/evm - Documentation/security/keys/trusted-encrypted.rst. Both dracut - (via 97masterkey and 98integrity) and systemd (via + will enable HMAC and digital signature validation and + HMAC creation and disable all further modification of policy. + + echo 0x80000006 >/evm + + will enable digital signature validation, permit + modification of EVM-protected metadata and + disable all further modification of policy + + Note that once a key has been loaded, it will no longer be + possible to enable metadata modification. + + Until key loading has been signaled EVM can not create + or validate the 'security.evm' xattr, but returns + INTEGRITY_UNKNOWN. Loading keys and signaling EVM + should be done as early as possible. Normally this is + done in the initramfs, which has already been measured + as part of the trusted boot. For more information on + creating and loading existing trusted/encrypted keys, + refer to: + Documentation/security/keys/trusted-encrypted.rst. Both + dracut (via 97masterkey and 98integrity) and systemd (via core/ima-setup) have support for loading keys at boot time. -- cgit v1.2.3 From da1b0029f527a9b4204e90ba6f14ee139fd76f9e Mon Sep 17 00:00:00 2001 From: Mimi Zohar Date: Thu, 29 Sep 2016 10:04:52 -0400 Subject: ima: support new "hash" and "dont_hash" policy actions The builtin ima_appraise_tcb policy, which is specified on the boot command line, can be replaced with a custom policy, normally early in the boot process. Custom policies can be more restrictive in some ways, like requiring file signatures, but can be less restrictive in other ways, like not appraising mutable files. With a less restrictive policy in place, files in the builtin policy might not be hashed and labeled with a security.ima hash. On reboot, files which should be labeled in the ima_appraise_tcb are not labeled, possibly preventing the system from booting properly. To resolve this problem, this patch extends the existing IMA policy actions "measure", "dont_measure", "appraise", "dont_appraise", and "audit" with "hash" and "dont_hash". The new "hash" action will write the file hash as security.ima, but without requiring the file to be appraised as well. For example, the builtin ima_appraise_tcb policy includes the rule, "appraise fowner=0". Adding the "hash fowner=0" rule to a custom policy, will cause the needed file hashes to be calculated and written as security.ima xattrs. Signed-off-by: Mimi Zohar Signed-off-by: Stefan Berger --- Documentation/ABI/testing/ima_policy | 3 ++- security/integrity/ima/ima_api.c | 2 +- security/integrity/ima/ima_appraise.c | 16 +++++++++------- security/integrity/ima/ima_main.c | 12 ++++++++++++ security/integrity/ima/ima_policy.c | 30 ++++++++++++++++++++++++++++-- security/integrity/integrity.h | 23 +++++++++++++---------- 6 files changed, 65 insertions(+), 21 deletions(-) (limited to 'Documentation/ABI') diff --git a/Documentation/ABI/testing/ima_policy b/Documentation/ABI/testing/ima_policy index e76432b9954d..2028f2d093b2 100644 --- a/Documentation/ABI/testing/ima_policy +++ b/Documentation/ABI/testing/ima_policy @@ -17,7 +17,8 @@ Description: rule format: action [condition ...] - action: measure | dont_measure | appraise | dont_appraise | audit + action: measure | dont_measure | appraise | dont_appraise | + audit | hash | dont_hash condition:= base | lsm [option] base: [[func=] [mask=] [fsmagic=] [fsuuid=] [uid=] [euid=] [fowner=]] diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c index c7e8db0ea4c0..877f446fdca2 100644 --- a/security/integrity/ima/ima_api.c +++ b/security/integrity/ima/ima_api.c @@ -174,7 +174,7 @@ err_out: */ int ima_get_action(struct inode *inode, int mask, enum ima_hooks func, int *pcr) { - int flags = IMA_MEASURE | IMA_AUDIT | IMA_APPRAISE; + int flags = IMA_MEASURE | IMA_AUDIT | IMA_APPRAISE | IMA_HASH; flags &= ima_policy_flag; diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index ea1245606a14..f2803a40ff82 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -46,14 +46,15 @@ bool is_ima_appraise_enabled(void) /* * ima_must_appraise - set appraise flag * - * Return 1 to appraise + * Return 1 to appraise or hash */ int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func) { if (!ima_appraise) return 0; - return ima_match_policy(inode, func, mask, IMA_APPRAISE, NULL); + return ima_match_policy(inode, func, mask, IMA_APPRAISE | IMA_HASH, + NULL); } static int ima_fix_xattr(struct dentry *dentry, @@ -324,7 +325,8 @@ void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file) if (test_bit(IMA_DIGSIG, &iint->atomic_flags)) return; - if (iint->ima_file_status != INTEGRITY_PASS) + if ((iint->ima_file_status != INTEGRITY_PASS) && + !(iint->flags & IMA_HASH)) return; rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo); @@ -349,19 +351,19 @@ void ima_inode_post_setattr(struct dentry *dentry) { struct inode *inode = d_backing_inode(dentry); struct integrity_iint_cache *iint; - int must_appraise; + int action; if (!(ima_policy_flag & IMA_APPRAISE) || !S_ISREG(inode->i_mode) || !(inode->i_opflags & IOP_XATTR)) return; - must_appraise = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR); - if (!must_appraise) + action = ima_must_appraise(inode, MAY_ACCESS, POST_SETATTR); + if (!action) __vfs_removexattr(dentry, XATTR_NAME_IMA); iint = integrity_iint_find(inode); if (iint) { set_bit(IMA_CHANGE_ATTR, &iint->atomic_flags); - if (!must_appraise) + if (!action) clear_bit(IMA_UPDATE_XATTR, &iint->atomic_flags); } } diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c index edf4e0717494..be1987e13c43 100644 --- a/security/integrity/ima/ima_main.c +++ b/security/integrity/ima/ima_main.c @@ -243,6 +243,18 @@ static int process_measurement(struct file *file, char *buf, loff_t size, if ((action & IMA_MEASURE) && (iint->measured_pcrs & (0x1 << pcr))) action ^= IMA_MEASURE; + /* HASH sets the digital signature and update flags, nothing else */ + if ((action & IMA_HASH) && + !(test_bit(IMA_DIGSIG, &iint->atomic_flags))) { + xattr_len = ima_read_xattr(file_dentry(file), &xattr_value); + if ((xattr_value && xattr_len > 2) && + (xattr_value->type == EVM_IMA_XATTR_DIGSIG)) + set_bit(IMA_DIGSIG, &iint->atomic_flags); + iint->flags |= IMA_HASHED; + action ^= IMA_HASH; + set_bit(IMA_UPDATE_XATTR, &iint->atomic_flags); + } + /* Nothing to do, just return existing appraised status */ if (!action) { if (must_appraise) diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c index ee4613fa5840..93dcf1bf92a8 100644 --- a/security/integrity/ima/ima_policy.c +++ b/security/integrity/ima/ima_policy.c @@ -40,6 +40,8 @@ #define APPRAISE 0x0004 /* same as IMA_APPRAISE */ #define DONT_APPRAISE 0x0008 #define AUDIT 0x0040 +#define HASH 0x0100 +#define DONT_HASH 0x0200 #define INVALID_PCR(a) (((a) < 0) || \ (a) >= (FIELD_SIZEOF(struct integrity_iint_cache, measured_pcrs) * 8)) @@ -380,8 +382,10 @@ int ima_match_policy(struct inode *inode, enum ima_hooks func, int mask, action |= entry->flags & IMA_ACTION_FLAGS; action |= entry->action & IMA_DO_MASK; - if (entry->action & IMA_APPRAISE) + if (entry->action & IMA_APPRAISE) { action |= get_subaction(entry, func); + action ^= IMA_HASH; + } if (entry->action & IMA_DO_MASK) actmask &= ~(entry->action | entry->action << 1); @@ -521,7 +525,7 @@ enum { Opt_err = -1, Opt_measure = 1, Opt_dont_measure, Opt_appraise, Opt_dont_appraise, - Opt_audit, + Opt_audit, Opt_hash, Opt_dont_hash, Opt_obj_user, Opt_obj_role, Opt_obj_type, Opt_subj_user, Opt_subj_role, Opt_subj_type, Opt_func, Opt_mask, Opt_fsmagic, @@ -538,6 +542,8 @@ static match_table_t policy_tokens = { {Opt_appraise, "appraise"}, {Opt_dont_appraise, "dont_appraise"}, {Opt_audit, "audit"}, + {Opt_hash, "hash"}, + {Opt_dont_hash, "dont_hash"}, {Opt_obj_user, "obj_user=%s"}, {Opt_obj_role, "obj_role=%s"}, {Opt_obj_type, "obj_type=%s"}, @@ -671,6 +677,22 @@ static int ima_parse_rule(char *rule, struct ima_rule_entry *entry) entry->action = AUDIT; break; + case Opt_hash: + ima_log_string(ab, "action", "hash"); + + if (entry->action != UNKNOWN) + result = -EINVAL; + + entry->action = HASH; + break; + case Opt_dont_hash: + ima_log_string(ab, "action", "dont_hash"); + + if (entry->action != UNKNOWN) + result = -EINVAL; + + entry->action = DONT_HASH; + break; case Opt_func: ima_log_string(ab, "func", args[0].from); @@ -1040,6 +1062,10 @@ int ima_policy_show(struct seq_file *m, void *v) seq_puts(m, pt(Opt_dont_appraise)); if (entry->action & AUDIT) seq_puts(m, pt(Opt_audit)); + if (entry->action & HASH) + seq_puts(m, pt(Opt_hash)); + if (entry->action & DONT_HASH) + seq_puts(m, pt(Opt_dont_hash)); seq_puts(m, " "); diff --git a/security/integrity/integrity.h b/security/integrity/integrity.h index c64ea8f88f66..50a8e3365df7 100644 --- a/security/integrity/integrity.h +++ b/security/integrity/integrity.h @@ -25,6 +25,8 @@ #define IMA_COLLECTED 0x00000020 #define IMA_AUDIT 0x00000040 #define IMA_AUDITED 0x00000080 +#define IMA_HASH 0x00000100 +#define IMA_HASHED 0x00000200 /* iint cache flags */ #define IMA_ACTION_FLAGS 0xff000000 @@ -35,19 +37,20 @@ #define EVM_IMMUTABLE_DIGSIG 0x08000000 #define IMA_DO_MASK (IMA_MEASURE | IMA_APPRAISE | IMA_AUDIT | \ - IMA_APPRAISE_SUBMASK) + IMA_HASH | IMA_APPRAISE_SUBMASK) #define IMA_DONE_MASK (IMA_MEASURED | IMA_APPRAISED | IMA_AUDITED | \ - IMA_COLLECTED | IMA_APPRAISED_SUBMASK) + IMA_HASHED | IMA_COLLECTED | \ + IMA_APPRAISED_SUBMASK) /* iint subaction appraise cache flags */ -#define IMA_FILE_APPRAISE 0x00000100 -#define IMA_FILE_APPRAISED 0x00000200 -#define IMA_MMAP_APPRAISE 0x00000400 -#define IMA_MMAP_APPRAISED 0x00000800 -#define IMA_BPRM_APPRAISE 0x00001000 -#define IMA_BPRM_APPRAISED 0x00002000 -#define IMA_READ_APPRAISE 0x00004000 -#define IMA_READ_APPRAISED 0x00008000 +#define IMA_FILE_APPRAISE 0x00001000 +#define IMA_FILE_APPRAISED 0x00002000 +#define IMA_MMAP_APPRAISE 0x00004000 +#define IMA_MMAP_APPRAISED 0x00008000 +#define IMA_BPRM_APPRAISE 0x00010000 +#define IMA_BPRM_APPRAISED 0x00020000 +#define IMA_READ_APPRAISE 0x00040000 +#define IMA_READ_APPRAISED 0x00080000 #define IMA_APPRAISE_SUBMASK (IMA_FILE_APPRAISE | IMA_MMAP_APPRAISE | \ IMA_BPRM_APPRAISE | IMA_READ_APPRAISE) #define IMA_APPRAISED_SUBMASK (IMA_FILE_APPRAISED | IMA_MMAP_APPRAISED | \ -- cgit v1.2.3