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

[Stefan Berger <stefanb@linux.ibm.com>]

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 <kam@juniper.net>

Tested-by: Stefan Berger <stefanb@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