[PATCH v3 1/2] ima: discard modsig when detached data cannot be supplied
Jérémy Jean
Jeremy.Jean at oss.cyber.gouv.fr
Wed Oct 21 21:01:46 UTC 2026
ima_collect_modsig() supplies the file contents to the parsed PKCS#7
message as detached data. If the message already contains embedded data,
pkcs7_supply_detached_data() returns -EINVAL, but IMA ignores the error.
ima_modsig_verify() then verifies the embedded data instead of the file
being appraised.
Make ima_collect_modsig() report whether the file data was supplied,
and discard the modsig if it was not.
Fixes: 15588227e086 ("ima: Collect modsig")
Cc: stable at vger.kernel.org
Signed-off-by: Jérémy Jean <Jeremy.Jean at oss.cyber.gouv.fr>
---
v1: https://lore.kernel.org/all/20260822082434.489470-2-Jeremy.Jean@oss.cyber.gouv.fr/
v2: https://lore.kernel.org/all/20260924085516.3111521-2-Jeremy.Jean@oss.cyber.gouv.fr/
Documentation/security/IMA-templates.rst | 3 ++-
security/integrity/ima/ima.h | 7 ++++---
security/integrity/ima/ima_api.c | 10 +++++++---
security/integrity/ima/ima_main.c | 2 +-
security/integrity/ima/ima_modsig.c | 16 +++++++++++-----
security/integrity/ima/ima_template_lib.c | 4 ++--
6 files changed, 27 insertions(+), 15 deletions(-)
diff --git a/Documentation/security/IMA-templates.rst b/Documentation/security/IMA-templates.rst
index 15b4add314fc..de7a3dfee33d 100644
--- a/Documentation/security/IMA-templates.rst
+++ b/Documentation/security/IMA-templates.rst
@@ -69,7 +69,8 @@ descriptors by adding their identifier to the format string
algorithm (field format: <hash algo>:digest);
- 'd-ngv2': same as d-ng, but prefixed with the "ima" or "verity" digest type
(field format: <digest type>:<hash algo>:digest);
- - 'd-modsig': the digest of the event without the appended modsig;
+ - 'd-modsig': the digest of the event without the appended modsig, empty
+ when no signature digest can be exported;
- 'n-ng': the name of the event, without size limitations;
- 'sig': the file signature, based on either the file's/fsverity's digest[1],
or the EVM portable signature, if 'security.ima' contains a file hash.
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 10214f73ca1e..62be9461de88 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -431,7 +431,7 @@ int ima_get_action(struct mnt_idmap *idmap, struct inode *inode,
int ima_must_measure(struct inode *inode, int mask, enum ima_hooks func);
int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
void *buf, loff_t size, enum hash_algo algo,
- struct modsig *modsig);
+ struct modsig **modsig);
void ima_store_measurement(struct ima_iint_cache *iint, struct file *file,
const unsigned char *filename,
struct evm_ima_xattr_data *xattr_value,
@@ -559,7 +559,7 @@ static inline void __init init_ima_appraise_lsm(const struct lsm_id *lsmid)
#ifdef CONFIG_IMA_APPRAISE_MODSIG
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);
+bool ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size);
int ima_get_modsig_digest(const struct modsig *modsig, enum hash_algo *algo,
const u8 **digest, u32 *digest_size);
int ima_get_raw_modsig(const struct modsig *modsig, const void **data,
@@ -572,9 +572,10 @@ 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,
+static inline bool ima_collect_modsig(struct modsig *modsig, const void *buf,
loff_t size)
{
+ return false;
}
static inline int ima_get_modsig_digest(const struct modsig *modsig,
diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 122d127e108d..00b83b4538ab 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -235,6 +235,8 @@ static bool ima_get_verity_digest(struct ima_iint_cache *iint,
*
* Calculate the file hash, if it doesn't already exist,
* storing the measurement and i_version in the iint.
+ * If modsig is provided, discard it when detached data cannot be supplied
+ * so ordinary measurement and xattr appraisal can proceed.
*
* Must be called with iint->mutex held.
*
@@ -242,7 +244,7 @@ static bool ima_get_verity_digest(struct ima_iint_cache *iint,
*/
int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
void *buf, loff_t size, enum hash_algo algo,
- struct modsig *modsig)
+ struct modsig **modsig)
{
const char *audit_cause = "failed";
struct inode *inode = file_inode(file);
@@ -262,8 +264,10 @@ int ima_collect_measurement(struct ima_iint_cache *iint, struct file *file,
* the file digest without collecting the modsig in a previous
* measurement rule.
*/
- if (modsig)
- ima_collect_modsig(modsig, buf, size);
+ if (modsig && *modsig && !ima_collect_modsig(*modsig, buf, size)) {
+ ima_free_modsig(*modsig);
+ *modsig = NULL;
+ }
if (iint->flags & IMA_COLLECTED)
goto out;
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index ab1e53b3210d..561fbd976a91 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -422,7 +422,7 @@ 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, modsig);
+ 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 632c746fd81e..f73d6f1b71c0 100644
--- a/security/integrity/ima/ima_modsig.c
+++ b/security/integrity/ima/ima_modsig.c
@@ -96,8 +96,12 @@ int ima_read_modsig(enum ima_hooks func, const void *buf, loff_t buf_len,
* 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.
+ *
+ * Digest export is best-effort; not all signatures expose a single digest.
+ *
+ * Return: true if the file data was supplied, false otherwise.
*/
-void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size)
+bool ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size)
{
int rc;
@@ -109,11 +113,13 @@ void ima_collect_modsig(struct modsig *modsig, const void *buf, loff_t size)
sizeof(struct module_signature);
rc = pkcs7_supply_detached_data(modsig->pkcs7_msg, buf, size);
if (rc)
- return;
+ return false;
+
+ /* Digest export failure does not preclude signature verification. */
+ pkcs7_get_digest(modsig->pkcs7_msg, &modsig->digest,
+ &modsig->digest_size, &modsig->hash_algo);
- /* Ask the PKCS7 code to calculate the file hash. */
- rc = pkcs7_get_digest(modsig->pkcs7_msg, &modsig->digest,
- &modsig->digest_size, &modsig->hash_algo);
+ return true;
}
int ima_modsig_verify(struct key *keyring, const struct modsig *modsig)
diff --git a/security/integrity/ima/ima_template_lib.c b/security/integrity/ima/ima_template_lib.c
index 8a89236f926c..1be78612394a 100644
--- a/security/integrity/ima/ima_template_lib.c
+++ b/security/integrity/ima/ima_template_lib.c
@@ -478,8 +478,8 @@ int ima_eventdigest_modsig_init(struct ima_event_data *event_data,
if (rc)
return rc;
else if (hash_algo == HASH_ALGO__LAST || cur_digestsize == 0)
- /* There was some error collecting the digest. */
- return -EINVAL;
+ /* Keep the ordinary measurement without an exported digest. */
+ return 0;
}
return ima_eventdigest_init_common(cur_digest, cur_digestsize,
--
2.47.3
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