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Message-Id: <874llhoz89.fsf@morokweng.localdomain>
Date: Thu, 15 Mar 2018 17:33:42 -0300
From: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: "Serge E. Hallyn" <serge@...lyn.com>,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, James Morris <jmorris@...ei.org>,
Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Subject: Re: [PATCH 3/4] ima: Improvements in ima_appraise_measurement()
Mimi Zohar <zohar@...ux.vnet.ibm.com> writes:
> On Wed, 2018-03-14 at 21:03 -0300, Thiago Jung Bauermann wrote:
>> Hello Serge,
>>
>> Thanks for quickly reviewing these patches!
>>
>> Serge E. Hallyn <serge@...lyn.com> writes:
>>
>> > Quoting Thiago Jung Bauermann (bauerman@...ux.vnet.ibm.com):
>> >> From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
>> >> @@ -241,16 +241,20 @@ int ima_appraise_measurement(enum ima_hooks func,
>> >> }
>> >>
>> >> status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
>> >> - if ((status != INTEGRITY_PASS) &&
>> >> - (status != INTEGRITY_PASS_IMMUTABLE) &&
>> >> - (status != INTEGRITY_UNKNOWN)) {
>> >> - if ((status == INTEGRITY_NOLABEL)
>> >> - || (status == INTEGRITY_NOXATTRS))
>> >> - cause = "missing-HMAC";
>> >> - else if (status == INTEGRITY_FAIL)
>> >> - cause = "invalid-HMAC";
>> >> + switch (status) {
>> >> + case INTEGRITY_PASS:
>> >> + case INTEGRITY_PASS_IMMUTABLE:
>> >> + case INTEGRITY_UNKNOWN:
>> >
>> > Wouldn't it be more future-proof to replace this with a 'default', or
>> > to at least add a "default: BUG()" to catch new status values?
>>
>> I agree. I like the "default: BUG()" option.
>
> Agreed. I would put it at the end after INTEGRITY_FAIL.
Ok, what about the version below?
>>
>> >> + break;
>> >> + case INTEGRITY_NOXATTRS: /* No EVM protected xattrs. */
>> >> + case INTEGRITY_NOLABEL: /* No security.evm xattr. */
>> >> + cause = "missing-HMAC";
>> >> + goto out;
>> >> + case INTEGRITY_FAIL: /* Invalid HMAC/signature. */
>> >> + cause = "invalid-HMAC";
>> >> goto out;
>> >> }
>> >> +
>> >> switch (xattr_value->type) {
>> >> case IMA_XATTR_DIGEST_NG:
>> >> /* first byte contains algorithm id */
>> >> @@ -316,17 +320,20 @@ int ima_appraise_measurement(enum ima_hooks func,
>> >> integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
>> >> op, cause, rc, 0);
>> >> } else if (status != INTEGRITY_PASS) {
>> >> + /* Fix mode, but don't replace file signatures. */
>> >> if ((ima_appraise & IMA_APPRAISE_FIX) &&
>> >> (!xattr_value ||
>> >> xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
>> >> if (!ima_fix_xattr(dentry, iint))
>> >> status = INTEGRITY_PASS;
>> >> - } else if ((inode->i_size == 0) &&
>> >> - (iint->flags & IMA_NEW_FILE) &&
>> >> - (xattr_value &&
>> >> - xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
>> >> + }
>> >> +
>> >> + /* Permit new files with file signatures, but without data. */
>> >> + if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
>> >
>> > This may be correct, but it's not identical to what you're replacing.
>> > Since in either case you're setting status to INTEGRITY_PASS the final
>> > result is the same, but with a few extra possible steps. Not sure
>> > whether that matters.
>>
>> Good point. I'll have to defer this one to Mimi though.
>
> The end result is the same, but add some needed comments.
The patch is unchanged here, then.
--
Thiago Jung Bauermann
IBM Linux Technology Center
>From 343bf4ed2974421e254fb4d5cd79aed79c66f016 Mon Sep 17 00:00:00 2001
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Date: Mon, 21 Aug 2017 19:28:51 -0300
Subject: [PATCH] ima: Improvements in ima_appraise_measurement()
Replace nested ifs in the EVM xattr verification logic with a switch
statement, making the code easier to understand.
Also, add comments to the if statements in the out section and constify the
cause variable.
Signed-off-by: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
---
security/integrity/ima/ima_appraise.c | 35 ++++++++++++++++++++++-------------
1 file changed, 22 insertions(+), 13 deletions(-)
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index 0c5f94b7b9c3..8bd7a0733e51 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -215,7 +215,7 @@ int ima_appraise_measurement(enum ima_hooks func,
int xattr_len, int opened)
{
static const char op[] = "appraise_data";
- char *cause = "unknown";
+ const char *cause = "unknown";
struct dentry *dentry = file_dentry(file);
struct inode *inode = d_backing_inode(dentry);
enum integrity_status status = INTEGRITY_UNKNOWN;
@@ -241,16 +241,22 @@ int ima_appraise_measurement(enum ima_hooks func,
}
status = evm_verifyxattr(dentry, XATTR_NAME_IMA, xattr_value, rc, iint);
- if ((status != INTEGRITY_PASS) &&
- (status != INTEGRITY_PASS_IMMUTABLE) &&
- (status != INTEGRITY_UNKNOWN)) {
- if ((status == INTEGRITY_NOLABEL)
- || (status == INTEGRITY_NOXATTRS))
- cause = "missing-HMAC";
- else if (status == INTEGRITY_FAIL)
- cause = "invalid-HMAC";
+ switch (status) {
+ case INTEGRITY_PASS:
+ case INTEGRITY_PASS_IMMUTABLE:
+ case INTEGRITY_UNKNOWN:
+ break;
+ case INTEGRITY_NOXATTRS: /* No EVM protected xattrs. */
+ case INTEGRITY_NOLABEL: /* No security.evm xattr. */
+ cause = "missing-HMAC";
+ goto out;
+ case INTEGRITY_FAIL: /* Invalid HMAC/signature. */
+ cause = "invalid-HMAC";
goto out;
+ default:
+ WARN_ONCE(true, "Unexpected integrity status %d\n", status);
}
+
switch (xattr_value->type) {
case IMA_XATTR_DIGEST_NG:
/* first byte contains algorithm id */
@@ -316,17 +322,20 @@ int ima_appraise_measurement(enum ima_hooks func,
integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
op, cause, rc, 0);
} else if (status != INTEGRITY_PASS) {
+ /* Fix mode, but don't replace file signatures. */
if ((ima_appraise & IMA_APPRAISE_FIX) &&
(!xattr_value ||
xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
if (!ima_fix_xattr(dentry, iint))
status = INTEGRITY_PASS;
- } else if ((inode->i_size == 0) &&
- (iint->flags & IMA_NEW_FILE) &&
- (xattr_value &&
- xattr_value->type == EVM_IMA_XATTR_DIGSIG)) {
+ }
+
+ /* Permit new files with file signatures, but without data. */
+ if (inode->i_size == 0 && iint->flags & IMA_NEW_FILE &&
+ xattr_value && xattr_value->type == EVM_IMA_XATTR_DIGSIG) {
status = INTEGRITY_PASS;
}
+
integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode, filename,
op, cause, rc, 0);
} else {
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