From: Mimi Zohar <zohar@linux.vnet.ibm.com>
To: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>,
linux-integrity@vger.kernel.org
Cc: linux-security-module@vger.kernel.org, keyrings@vger.kernel.org,
linux-crypto@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
linux-kernel@vger.kernel.org,
Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
James Morris <james.l.morris@oracle.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
David Howells <dhowells@redhat.com>,
David Woodhouse <dwmw2@infradead.org>,
Jessica Yu <jeyu@redhat.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Herbert Xu <herbert@gondor.apana.org.au>,
"David S. Miller" <davem@davemloft.net>,
"AKASHI, Takahiro" <takahiro.akashi@linaro.org>
Subject: Re: [PATCH v5 17/18] ima: Implement support for module-style appended signatures
Date: Tue, 31 Oct 2017 09:31:35 -0400 [thread overview]
Message-ID: <1509456695.3583.226.camel@linux.vnet.ibm.com> (raw)
In-Reply-To: <20171018005331.2688-18-bauerman@linux.vnet.ibm.com>
On Tue, 2017-10-17 at 22:53 -0200, Thiago Jung Bauermann wrote:
Below are a few additional comments.
> @@ -200,18 +239,28 @@ int ima_read_xattr(struct dentry *dentry,
> */
> int ima_appraise_measurement(enum ima_hooks func,
> struct integrity_iint_cache *iint,
> - struct file *file, const unsigned char *filename,
> - struct evm_ima_xattr_data *xattr_value,
> - int xattr_len, int opened)
> + struct file *file, const void *buf, loff_t size,
> + const unsigned char *filename,
> + struct evm_ima_xattr_data **xattr_value_,
> + int *xattr_len_, int opened)
> {
> static const char op[] = "appraise_data";
> const char *cause = "unknown";
> struct dentry *dentry = file_dentry(file);
> struct inode *inode = d_backing_inode(dentry);
> enum integrity_status status = INTEGRITY_UNKNOWN;
> - int rc = xattr_len, hash_start = 0;
> + struct evm_ima_xattr_data *xattr_value = *xattr_value_;
> + int xattr_len = *xattr_len_, rc = xattr_len, hash_start = 0;
> + bool appraising_modsig = false;
> +
> + if (iint->flags & IMA_MODSIG_ALLOWED &&
> + !ima_read_modsig(func, buf, size, &xattr_value, &xattr_len)) {
> + appraising_modsig = true;
> + rc = xattr_len;
> + }
>
> - if (!(inode->i_opflags & IOP_XATTR))
> + /* If not appraising a modsig, we need an xattr. */
> + if (!appraising_modsig && !(inode->i_opflags & IOP_XATTR))
> return INTEGRITY_UNKNOWN;
>
> if (rc <= 0) {
> @@ -235,6 +284,9 @@ int ima_appraise_measurement(enum ima_hooks func,
> case INTEGRITY_UNKNOWN:
> break;
> case INTEGRITY_NOXATTRS: /* No EVM protected xattrs. */
> + /* It's fine not to have xattrs when using a modsig. */
> + if (appraising_modsig)
> + break;
> case INTEGRITY_NOLABEL: /* No security.evm xattr. */
> cause = "missing-HMAC";
> goto out;
> @@ -242,6 +294,8 @@ int ima_appraise_measurement(enum ima_hooks func,
> cause = "invalid-HMAC";
> goto out;
> }
> +
> + retry:
> switch (xattr_value->type) {
> case IMA_XATTR_DIGEST_NG:
> /* first byte contains algorithm id */
> @@ -285,6 +339,61 @@ int ima_appraise_measurement(enum ima_hooks func,
> status = INTEGRITY_PASS;
> }
> break;
> + case IMA_MODSIG:
> + /*
> + * To avoid being tricked into an infinite loop, we don't allow
> + * a modsig stored in the xattr.
> + */
> + if (!appraising_modsig) {
> + status = INTEGRITY_UNKNOWN;
> + cause = "unknown-ima-data";
> + break;
> + }
> + rc = appraise_modsig(iint, xattr_value, xattr_len);
> + if (!rc) {
> + kfree(*xattr_value_);
> + *xattr_value_ = xattr_value;
> + *xattr_len_ = xattr_len;
> +
> + status = INTEGRITY_PASS;
> + break;
> + }
> +
> + ima_free_xattr_data(xattr_value);
> +
> + /*
> + * The appended signature failed verification. If there's a
> + * signature in the extended attribute, let's fall back to it.
> + */
> + if (inode->i_opflags & IOP_XATTR && *xattr_len_ != 0 &&
> + *xattr_len_ != -ENODATA) {
At this point, there was an appended signature verification failure.
If there isn't an xattr, for whatever reason, shouldn't we be
returning "invalid_signature" and "INTEGRITY_FAIL". If so, then the
above test could be simplified to check whether there is any data,
like this:
if ((inode->i_opflags & IOP_XATTR) && (*xattr_len_ > 0)) {
> + const char *modsig_cause = rc == -EOPNOTSUPP ?
> + "unknown" : "invalid-signature";
This can then be cleaned up as well.
> +
> + /* First, log that the modsig verification failed. */
> + integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
> + filename, op, modsig_cause, rc, 0);
I'm not sure that we want to audit intermediary signature verification
failures. Perhaps this audit message should be considered
"additional", meaning it is only emitted if the "integrity_audit" boot
command line option is enabled. Change the last field to 1 to
indicate it is an "additional" audit message.
> +
> + xattr_len = rc = *xattr_len_;
> + xattr_value = *xattr_value_;
> + appraising_modsig = false;
> +
> + if (rc > 0)
This test becomes redundant.
> + /* Process xattr contents. */
> + goto retry;
> +
> + /* Unexpected error reading xattr. */
> + status = INTEGRITY_UNKNOWN;
> + } else {
> + if (rc == -EOPNOTSUPP)
> + status = INTEGRITY_UNKNOWN;
> + else {
> + cause = "invalid-signature";
> + status = INTEGRITY_FAIL;
> + }
> + }
> + break;
I think the rest can be simplified to:
cause = "invalid-signature";
status = INTEGRITY_FAIL;
Mimi
next prev parent reply other threads:[~2017-10-31 13:31 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-18 0:53 [PATCH v5 00/18] Appended signatures support for IMA appraisal Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 01/18] ima: Remove redundant conditional operator Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 02/18] ima: Remove some superfluous parentheses Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 03/18] evm, ima: Remove " Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 04/18] evm, ima: Remove more " Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 05/18] ima: Simplify ima_eventsig_init Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 06/18] ima: Improvements in ima_appraise_measurement Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 07/18] integrity: Introduce struct evm_xattr Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 08/18] integrity: Select CONFIG_KEYS instead of depending on it Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 09/18] ima: Don't pass xattr value to EVM xattr verification Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 10/18] ima: Store measurement after appraisal Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 11/18] ima: Export func_tokens Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 12/18] MODSIGN: Export module signature definitions Thiago Jung Bauermann
2017-10-26 20:12 ` Mimi Zohar
2017-10-26 22:47 ` Thiago Jung Bauermann
2017-10-26 23:13 ` Mimi Zohar
2017-10-18 0:53 ` [PATCH v5 13/18] PKCS#7: Introduce pkcs7_get_message_sig and verify_pkcs7_message_sig Thiago Jung Bauermann
2017-10-26 20:12 ` Mimi Zohar
2017-10-18 0:53 ` [PATCH v5 14/18] integrity: Introduce integrity_keyring_from_id Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 15/18] ima: Add modsig appraise_type option for module-style appended signatures Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 16/18] ima: Add functions to read and verify a modsig signature Thiago Jung Bauermann
2017-10-18 0:53 ` [PATCH v5 17/18] ima: Implement support for module-style appended signatures Thiago Jung Bauermann
2017-10-31 13:31 ` Mimi Zohar [this message]
2017-10-18 0:53 ` [PATCH v5 18/18] ima: Write modsig to the measurement list Thiago Jung Bauermann
2017-10-26 20:07 ` Mimi Zohar
2017-10-26 22:02 ` Thiago Jung Bauermann
2017-10-26 20:53 ` [PATCH v5 00/18] Appended signatures support for IMA appraisal Mimi Zohar
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