Re: [PATCH] ima: Fix sigv3 signature handling for EVM_IMA_XATTR_DIGSIG

[Stefan Berger]

On 4/24/26 7:39 AM, Kamlesh Kumar wrote:
ima_get_hash_algo() only recognizes version 2 signatures when the xattr
type is EVM_IMA_XATTR_DIGSIG. Since sigv3 signatures also use
EVM_IMA_XATTR_DIGSIG as the xattr type, version 3 must be accepted as
well to correctly determine the hash algorithm.

Thanks. I tested this with your patch. I can sign now with evmctl 
ima_sign --v3 -a sha512 ... even if sha256 is the IMA default and IMA 
verifies it now. Before I had to use evmctl ima_sign --v3 -a sha256 ...


Additionally, ima_validate_rule() does not include IMA_SIGV3_REQUIRED in
the allowed flags bitmask for MODULE_CHECK, KEXEC_KERNEL_CHECK, and
KEXEC_INITRAMFS_CHECK hook functions. As a result, policy rules with
"appraise_type=sigv3" are rejected for these functions.

# echo "appraise func=KEXEC_KERNEL_CHECK appraise_type=sigv3" > 
/sys/kernel/security/ima/policy
-bash: echo: write error: Invalid argument

This rule is now accepted with your patch.


Add version 3 to the accepted versions in ima_get_hash_algo() for
EVM_IMA_XATTR_DIGSIG, and add IMA_SIGV3_REQUIRED to the allowed flags
for MODULE_CHECK, KEXEC_KERNEL_CHECK, and KEXEC_INITRAMFS_CHECK in
ima_validate_rule().

Signed-off-by: Kamlesh Kumar <k...@juniper.net>

Tested-by: Stefan Berger <stef...@linux.ibm.com>

---
  security/integrity/ima/ima_appraise.c | 5 +++--
  security/integrity/ima/ima_policy.c   | 3 ++-
  2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/security/integrity/ima/ima_appraise.c 
b/security/integrity/ima/ima_appraise.c
index de963b9f3634..2dd231567710 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -195,8 +195,9 @@ enum hash_algo ima_get_hash_algo(const struct 
evm_ima_xattr_data *xattr_value,
                return sig->hash_algo;
        case EVM_IMA_XATTR_DIGSIG:
                sig = (typeof(sig))xattr_value;
-               if (sig->version != 2 || xattr_len <= sizeof(*sig)
-                   || sig->hash_algo >= HASH_ALGO__LAST)
+               if ((sig->version != 2 && sig->version != 3) ||
+                   xattr_len <= sizeof(*sig) ||
+                   sig->hash_algo >= HASH_ALGO__LAST)
                        return ima_hash_algo;
                return sig->hash_algo;
        case IMA_XATTR_DIGEST_NG:
diff --git a/security/integrity/ima/ima_policy.c 
b/security/integrity/ima/ima_policy.c
index f7f940a76922..b1c010e8eb13 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -1313,7 +1313,8 @@ static bool ima_validate_rule(struct ima_rule_entry 
*entry)
                                     IMA_GID | IMA_EGID |
                                     IMA_FGROUP | IMA_DIGSIG_REQUIRED |
                                     IMA_PERMIT_DIRECTIO | IMA_MODSIG_ALLOWED |
-                                    IMA_CHECK_BLACKLIST | IMA_VALIDATE_ALGOS))
+                                    IMA_CHECK_BLACKLIST | IMA_VALIDATE_ALGOS |
+                                    IMA_SIGV3_REQUIRED))
                        return false;
  
  		break;

base-commit: 82bbd447199ff1441031d2eaf9afe041550cf525