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SubjectRe: [PATCH 3/4] ima: Improvements in ima_appraise_measurement()
Quoting Thiago Jung Bauermann (bauerman@linux.vnet.ibm.com):
> From: Mimi Zohar <zohar@linux.vnet.ibm.com>
>
> 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@linux.vnet.ibm.com>
> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
> ---
> security/integrity/ima/ima_appraise.c | 33 ++++++++++++++++++++-------------
> 1 file changed, 20 insertions(+), 13 deletions(-)
>
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index 0c5f94b7b9c3..dd10ecbdce45 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 +241,20 @@ 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?

> + 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.

> + 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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