[PATCH v10 10/12] ima: Collect modsig

Thiago Jung Bauermann
2019-04-18T03:52:51Z

Obtain the modsig and calculate its corresponding hash in
ima_collect_measurement().

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
---
security/integrity/ima/ima.h | 8 ++++-
security/integrity/ima/ima_api.c | 5 ++-
security/integrity/ima/ima_appraise.c | 2 +-
security/integrity/ima/ima_main.c | 2 +-
security/integrity/ima/ima_modsig.c | 50 ++++++++++++++++++++++++++-
5 files changed, 62 insertions(+), 5 deletions(-)

diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 9f69befd8674..e051477badf4 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -201,7 +201,7 @@ int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
int ima_must_measure(struct inode *inode, int mask, enum ima_hooks func);
int ima_collect_measurement(struct integrity_iint_cache *iint,
struct file *file, void *buf, loff_t size,
- enum hash_algo algo);
+ enum hash_algo algo, struct modsig *modsig);
void ima_store_measurement(struct integrity_iint_cache *iint, struct file *file,
const unsigned char *filename,
struct evm_ima_xattr_data *xattr_value,
@@ -302,6 +302,7 @@ static inline int ima_read_xattr(struct dentry *dentry,
bool ima_hook_supports_modsig(enum ima_hooks func);
int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
struct modsig **modsig);
+void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size);
void ima_free_modsig(struct modsig *modsig);
#else
static inline bool ima_hook_supports_modsig(enum ima_hooks func)
@@ -315,6 +316,11 @@ static inline int ima_read_modsig(enum ima_hooks func, const void *buf,
return -EOPNOTSUPP;
}

+static inline void ima_collect_modsig(struct modsig *modsig, const void *buf,
+ loff_t size)
+{
+}
+
static inline void ima_free_modsig(struct modsig *modsig)
{
}
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 0639d0631f2c..7c01b0a57a5a 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -198,7 +198,7 @@ int ima_get_action(struct inode *inode, const struct cred *cred, u32 secid,
*/
int ima_collect_measurement(struct integrity_iint_cache *iint,
struct file *file, void *buf, loff_t size,
- enum hash_algo algo)
+ enum hash_algo algo, struct modsig *modsig)
{
const char *audit_cause = "failed";
struct inode *inode = file_inode(file);
@@ -245,6 +245,9 @@ int ima_collect_measurement(struct integrity_iint_cache *iint,
memcpy(iint->ima_hash, &hash, length);
iint->version = i_version;

+ if (modsig)
+ ima_collect_modsig(modsig, buf, size);
+
/* Possibly temporary failure due to type of read (eg. O_DIRECT) */
if (!result)
iint->flags |= IMA_COLLECTED;
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index b8cc5897f16a..119034a59627 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -437,7 +437,7 @@ void ima_update_xattr(struct integrity_iint_cache *iint, struct file *file)
!(iint->flags & IMA_HASH))
return;

- rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo);
+ rc = ima_collect_measurement(iint, file, NULL, 0, ima_hash_algo, NULL);
if (rc < 0)
return;

diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 722d4e9c72ac..b5e44d03a0e3 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -289,7 +289,7 @@ static int process_measurement(struct file *file, const struct cred *cred,

hash_algo = ima_get_hash_algo(xattr_value, xattr_len);

- rc = ima_collect_measurement(iint, file, buf, size, hash_algo);
+ rc = ima_collect_measurement(iint, file, buf, size, hash_algo, modsig);
if (rc != 0 && rc != -EBADF && rc != -EINVAL)
goto out_locked;

diff --git a/security/integrity/ima/ima_modsig.c b/security/integrity/ima/ima_modsig.c
index ac0f44fb52ce..22a49f127437 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -17,6 +17,19 @@

struct modsig {
struct pkcs7_message *pkcs7_msg;
+
+ enum hash_algo hash_algo;
+
+ /* This digest will go in the 'd-modsig' field of the IMA template. */
+ const u8 *digest;
+ u32 digest_size;
+
+ /*
+ * This is what will go to the measurement list if the template requires
+ * storing the signature.
+ */
+ int raw_pkcs7_len;
+ u8 raw_pkcs7[];
};

/**
@@ -71,7 +84,8 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
sig_len = be32_to_cpu(sig->sig_len);
buf_len -= sig_len + sizeof(*sig);

- hdr = kmalloc(sizeof(*hdr), GFP_KERNEL);
+ /* Allocate sig_len additional bytes to hold the raw PKCS#7 data. */
+ hdr = kzalloc(sizeof(*hdr) + sig_len, GFP_KERNEL);
if (!hdr)
return -ENOMEM;

@@ -81,11 +95,45 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
return PTR_ERR(hdr->pkcs7_msg);
}

+ memcpy(hdr->raw_pkcs7, buf + buf_len, sig_len);
+ hdr->raw_pkcs7_len = sig_len;
+
+ /* We don't know the hash algorithm yet. */
+ hdr->hash_algo = HASH_ALGO__LAST;
+
*modsig = hdr;

return 0;
}

+/**
+ * ima_collect_modsig - Calculate the file hash without the appended signature.
+ *
+ * Since the modsig is part of the file contents, the hash used in its signature
+ * isn't the same one ordinarily calculated by IMA. Therefore PKCS7 code
+ * calculates a separate one for signature verification.
+ */
+void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size)
+{
+ int rc;
+
+ /*
+ * Provide the file contents (minus the appended sig) so that the PKCS7
+ * code can calculate the file hash.
+ */
+ size -= modsig->raw_pkcs7_len + strlen(MODULE_SIG_STRING) +
+ sizeof(struct module_signature);
+ rc = pkcs7_supply_detached_data(modsig->pkcs7_msg, buf, size);
+ if (rc)
+ return;
+
+ /* Ask the PKCS7 code to calculate the file hash. */
+ rc = pkcs7_get_digest(modsig->pkcs7_msg, &modsig->digest,
+ &modsig->digest_size, &modsig->hash_algo);
+ if (rc)
+ return;
+}
+
int ima_modsig_verify(struct key *keyring, const struct modsig *modsig)
{
return verify_pkcs7_message_sig(NULL, 0, modsig->pkcs7_msg, keyring,