[PATCH v6 23/25] evm: Remove dependency on 'integrity' LSM

From: Roberto Sassu
Date: Mon Nov 20 2023 - 12:41:52 EST

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From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>

Similarly to IMA, introduce EVM own integrity metadata (evm_iint_cache,
with EVM-specific fields from integrity_iint_cache), and reserve them from
the 'evm' LSM.

First, replace the integrity_iint_cache structure with evm_iint_cache in
various places of the EVM code.

Then, reserve space in the security blob for the evm_iint_cache structure,
so that retrieval always succeeds. Replace integrity_inode_get() and
integrity_iint_find() with evm_inode_get_iint(), to retrieve the
evm_iint_cache structure.

Initialize the new evm_iint_cache structure by registering
evm_inode_alloc_security() as implementation of the inode_alloc_security
LSM hook.

Since now IMA and EVM integrity metadata are disjoint, and always
available, remove the iint parameter from evm_verifyxattr() and always
retrieve the evm_iint_cache structure in evm_verify_hmac(), called by
evm_verifyxattr() and evm_verify_current_integrity().

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
include/linux/evm.h | 8 +---
security/integrity/evm/evm.h | 17 ++++++++
security/integrity/evm/evm_crypto.c | 5 +--
security/integrity/evm/evm_main.c | 63 ++++++++++++++-------------
security/integrity/ima/ima_appraise.c | 2 +-
5 files changed, 54 insertions(+), 41 deletions(-)

diff --git a/include/linux/evm.h b/include/linux/evm.h
index cb481eccc967..d48d6da32315 100644
--- a/include/linux/evm.h
+++ b/include/linux/evm.h
@@ -12,15 +12,12 @@
#include <linux/integrity.h>
#include <linux/xattr.h>

-struct integrity_iint_cache;
-
#ifdef CONFIG_EVM
extern int evm_set_key(void *key, size_t keylen);
extern enum integrity_status evm_verifyxattr(struct dentry *dentry,
const char *xattr_name,
void *xattr_value,
- size_t xattr_value_len,
- struct integrity_iint_cache *iint);
+ size_t xattr_value_len);
int evm_inode_init_security(struct inode *inode, struct inode *dir,
const struct qstr *qstr, struct xattr *xattrs,
int *xattr_count);
@@ -48,8 +45,7 @@ static inline int evm_set_key(void *key, size_t keylen)
static inline enum integrity_status evm_verifyxattr(struct dentry *dentry,
const char *xattr_name,
void *xattr_value,
- size_t xattr_value_len,
- struct integrity_iint_cache *iint)
+ size_t xattr_value_len)
{
return INTEGRITY_UNKNOWN;
}
diff --git a/security/integrity/evm/evm.h b/security/integrity/evm/evm.h
index 53bd7fec93fa..478b6fbca699 100644
--- a/security/integrity/evm/evm.h
+++ b/security/integrity/evm/evm.h
@@ -32,6 +32,23 @@ struct xattr_list {
bool enabled;
};

+/* EVM integrity metadata associated with an inode */
+struct evm_iint_cache {
+ unsigned long flags;
+ enum integrity_status evm_status:4;
+};
+
+extern struct lsm_blob_sizes evm_blob_sizes;
+
+static inline struct evm_iint_cache *
+evm_inode_get_iint(const struct inode *inode)
+{
+ struct evm_iint_cache *evm_iint_sec;
+
+ evm_iint_sec = inode->i_security + evm_blob_sizes.lbs_inode;
+ return evm_iint_sec;
+}
+
extern int evm_initialized;

#define EVM_ATTR_FSUUID 0x0001
diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
index b1ffd4cc0b44..c69422cc4a52 100644
--- a/security/integrity/evm/evm_crypto.c
+++ b/security/integrity/evm/evm_crypto.c
@@ -322,11 +322,10 @@ int evm_calc_hash(struct dentry *dentry, const char *req_xattr_name,
static int evm_is_immutable(struct dentry *dentry, struct inode *inode)
{
const struct evm_ima_xattr_data *xattr_data = NULL;
- struct integrity_iint_cache *iint;
+ struct evm_iint_cache *iint = evm_inode_get_iint(inode);
int rc = 0;

- iint = integrity_iint_find(inode);
- if (iint && (iint->flags & EVM_IMMUTABLE_DIGSIG))
+ if (iint->flags & EVM_IMMUTABLE_DIGSIG)
return 1;

/* Do this the hard way */
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 1e59a985b845..5aa5207a75e1 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -167,18 +167,20 @@ static int evm_find_protected_xattrs(struct dentry *dentry)
static enum integrity_status evm_verify_hmac(struct dentry *dentry,
const char *xattr_name,
char *xattr_value,
- size_t xattr_value_len,
- struct integrity_iint_cache *iint)
+ size_t xattr_value_len)
{
struct evm_ima_xattr_data *xattr_data = NULL;
struct signature_v2_hdr *hdr;
enum integrity_status evm_status = INTEGRITY_PASS;
struct evm_digest digest;
struct inode *inode;
+ struct evm_iint_cache *iint;
int rc, xattr_len, evm_immutable = 0;

- if (iint && (iint->evm_status == INTEGRITY_PASS ||
- iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
+ iint = evm_inode_get_iint(d_backing_inode(dentry));
+
+ if ((iint->evm_status == INTEGRITY_PASS ||
+ iint->evm_status == INTEGRITY_PASS_IMMUTABLE))
return iint->evm_status;

/* if status is not PASS, try to check again - against -ENOMEM */
@@ -243,8 +245,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
inode = d_backing_inode(dentry);

if (xattr_data->type == EVM_XATTR_PORTABLE_DIGSIG) {
- if (iint)
- iint->flags |= EVM_IMMUTABLE_DIGSIG;
+ iint->flags |= EVM_IMMUTABLE_DIGSIG;
evm_status = INTEGRITY_PASS_IMMUTABLE;
} else if (!IS_RDONLY(inode) &&
!(inode->i_sb->s_readonly_remount) &&
@@ -271,8 +272,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
pr_debug("digest: (%d) [%*phN]\n", digest.hdr.length, digest.hdr.length,
digest.digest);
out:
- if (iint)
- iint->evm_status = evm_status;
+ iint->evm_status = evm_status;
kfree(xattr_data);
return evm_status;
}
@@ -389,7 +389,6 @@ int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
* @xattr_name: requested xattr
* @xattr_value: requested xattr value
* @xattr_value_len: requested xattr value length
- * @iint: inode integrity metadata
*
* Calculate the HMAC for the given dentry and verify it against the stored
* security.evm xattr. For performance, use the xattr value and length
@@ -402,19 +401,13 @@ int evm_read_protected_xattrs(struct dentry *dentry, u8 *buffer,
*/
enum integrity_status evm_verifyxattr(struct dentry *dentry,
const char *xattr_name,
- void *xattr_value, size_t xattr_value_len,
- struct integrity_iint_cache *iint)
+ void *xattr_value, size_t xattr_value_len)
{
if (!evm_key_loaded() || !evm_protected_xattr(xattr_name))
return INTEGRITY_UNKNOWN;

- if (!iint) {
- iint = integrity_inode_get(d_backing_inode(dentry));
- if (!iint)
- return INTEGRITY_UNKNOWN;
- }
return evm_verify_hmac(dentry, xattr_name, xattr_value,
- xattr_value_len, iint);
+ xattr_value_len);
}
EXPORT_SYMBOL_GPL(evm_verifyxattr);

@@ -431,7 +424,7 @@ static enum integrity_status evm_verify_current_integrity(struct dentry *dentry)

if (!evm_key_loaded() || !S_ISREG(inode->i_mode) || evm_fixmode)
return INTEGRITY_PASS;
- return evm_verify_hmac(dentry, NULL, NULL, 0, NULL);
+ return evm_verify_hmac(dentry, NULL, NULL, 0);
}

/*
@@ -503,14 +496,14 @@ static int evm_protect_xattr(struct mnt_idmap *idmap,

evm_status = evm_verify_current_integrity(dentry);
if (evm_status == INTEGRITY_NOXATTRS) {
- struct integrity_iint_cache *iint;
+ struct evm_iint_cache *iint;

/* Exception if the HMAC is not going to be calculated. */
if (evm_hmac_disabled())
return 0;

- iint = integrity_iint_find(d_backing_inode(dentry));
- if (iint && (iint->flags & IMA_NEW_FILE))
+ iint = evm_inode_get_iint(d_backing_inode(dentry));
+ if ((iint->flags & IMA_NEW_FILE))
return 0;

/* exception for pseudo filesystems */
@@ -712,11 +705,9 @@ static int evm_inode_remove_acl(struct mnt_idmap *idmap, struct dentry *dentry,

static void evm_reset_status(struct inode *inode)
{
- struct integrity_iint_cache *iint;
+ struct evm_iint_cache *iint = evm_inode_get_iint(inode);

- iint = integrity_iint_find(inode);
- if (iint)
- iint->evm_status = INTEGRITY_UNKNOWN;
+ iint->evm_status = INTEGRITY_UNKNOWN;
}

/**
@@ -982,12 +973,11 @@ EXPORT_SYMBOL_GPL(evm_inode_init_security);
static void __maybe_unused
evm_post_path_mknod(struct mnt_idmap *idmap, struct dentry *dentry)
{
- struct integrity_iint_cache *iint;
+ struct evm_iint_cache *iint;

- iint = integrity_inode_get(d_backing_inode(dentry));
- if (iint)
- /* needed for successful verification of empty files */
- iint->flags |= IMA_NEW_FILE;
+ iint = evm_inode_get_iint(d_backing_inode(dentry));
+ /* needed for successful verification of empty files */
+ iint->flags |= IMA_NEW_FILE;
}

#ifdef CONFIG_EVM_LOAD_X509
@@ -1029,6 +1019,15 @@ static int __init init_evm(void)
return error;
}

+static int evm_inode_alloc_security(struct inode *inode)
+{
+ struct evm_iint_cache *evm_iint = evm_inode_get_iint(inode);
+
+ evm_iint->flags = 0UL;
+ evm_iint->evm_status = INTEGRITY_UNKNOWN;
+ return 0;
+}
+
static struct security_hook_list evm_hooks[] __ro_after_init = {
LSM_HOOK_INIT(inode_setattr, evm_inode_setattr),
LSM_HOOK_INIT(inode_post_setattr, evm_inode_post_setattr),
@@ -1041,6 +1040,7 @@ static struct security_hook_list evm_hooks[] __ro_after_init = {
LSM_HOOK_INIT(inode_removexattr, evm_inode_removexattr),
LSM_HOOK_INIT(inode_post_removexattr, evm_inode_post_removexattr),
LSM_HOOK_INIT(inode_init_security, evm_inode_init_security),
+ LSM_HOOK_INIT(inode_alloc_security, evm_inode_alloc_security),
#ifdef CONFIG_SECURITY_PATH
LSM_HOOK_INIT(path_post_mknod, evm_post_path_mknod),
#endif
@@ -1064,7 +1064,8 @@ int __init init_evm_lsm(void)
return 0;
}

-static struct lsm_blob_sizes evm_blob_sizes __ro_after_init = {
+struct lsm_blob_sizes evm_blob_sizes __ro_after_init = {
+ .lbs_inode = sizeof(struct evm_iint_cache),
.lbs_xattr_count = 1,
};

diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index b0b96c263961..89125efb7e06 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -519,7 +519,7 @@ int ima_appraise_measurement(enum ima_hooks func,
}

status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value,
- rc < 0 ? 0 : rc, NULL);
+ rc < 0 ? 0 : rc);
switch (status) {
case INTEGRITY_PASS:
case INTEGRITY_PASS_IMMUTABLE:
--
2.34.1

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