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Verify an fs-verity file digest based signature

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ima-evm-utils does not attempt to calculate or even read the fs-verity
file hash, but can verify the fs-verity signature based on the fsverity
file hash, both contained in the measurement list record.

Example:
evmctl ima_measurement --key <DER encoded public key> \
 --verify-sig /sys/kernel/security/ima/binary_runtime_measurements

Modify 'sig' argument of verify_hash() to be the full xattr in order to
differentiate signatures types.

Note:
Kernel commit b1aaab22e263 ("ima: pass full xattr with the signature")
added the 'type' to signature_v2_hdr struct, which hasn't been reflected
here. (todo)

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
This commit is contained in:
Mimi Zohar
2021-11-24 08:35:20 -05:00
parent fc46af121e
commit 3d77138811
2 changed files with 76 additions and 14 deletions
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11
src/evmctl.c
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@@ -918,7 +918,7 @@ static int verify_evm(const char *file)
return mdlen;
assert(mdlen <= sizeof(hash));
return verify_hash(file, hash, mdlen, sig + 1, len - 1);
return verify_hash(file, hash, mdlen, sig, len);
}
static int cmd_verify_evm(struct command *cmd)
@@ -1583,7 +1583,8 @@ void ima_ng_show(struct template_entry *entry)
fieldp += field_len;
total_len -= field_len;
if (!strcmp(entry->name, "ima-sig")) {
if (!strcmp(entry->name, "ima-sig") ||
!strcmp(entry->name, "ima-sigv2")) {
/* get signature */
field_len = *(uint32_t *)fieldp;
fieldp += sizeof(field_len);
@@ -1629,11 +1630,17 @@ void ima_ng_show(struct template_entry *entry)
log_info(" ");
log_dump(sig, sig_len);
}
/*
* Either verify the signature against the hash contained in
* the measurement list or calculate the hash.
*/
if (verify_list_sig)
err = ima_verify_signature(path, sig, sig_len,
digest, digest_len);
else
err = ima_verify_signature(path, sig, sig_len, NULL, 0);
if (!err && imaevm_params.verbose > LOG_INFO)
log_info("%s: verification is OK\n", path);
} else {