Re: [PATCH v2 08/12] evm: Allow xattr/attr operations for portable signatures if check fails
From: Mimi Zohar <zohar@linux.ibm.com>
Date: 2020-09-17 12:38:00
Also in:
linux-integrity, lkml
Hi Roberto, "if check fails" in the Subject line is unnecessary. On Fri, 2020-09-04 at 11:26 +0200, Roberto Sassu wrote:
If files with portable signatures are copied from one location to another or are extracted from an archive, verification can temporarily fail until all xattrs/attrs are set in the destination. Only portable signatures may be moved or copied from one file to another, as they don't depend on system-specific information such as the inode generation. Instead portable signatures must include security.ima. Unlike other security.evm types, EVM portable signatures are also immutable. Thus, it wouldn't be a problem to allow xattr/attr operations when verification fails, as portable signatures will never be replaced with an HMAC on possibly corrupted xattrs/attrs. This patch first introduces a new integrity status called INTEGRITY_FAIL_IMMUTABLE, that allows callers of evm_verify_current_integrity() to detect that a portable signature didn't pass verification and then adds an exception in evm_protect_xattr() and evm_inode_setattr() for this status and returns 0 instead of -EPERM. Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com> Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
< snip >
quoted hunk ↗ jump to hunk
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c index 05be1ad3e6f3..a5dab1ac9374 100644 --- a/security/integrity/evm/evm_main.c +++ b/security/integrity/evm/evm_main.c@@ -358,6 +364,12 @@ static int evm_protect_xattr(struct dentry *dentry, const char *xattr_name, -EPERM, 0); } out: + /* Writing other xattrs is safe for portable signatures, as portable + * signatures are immutable and can never be updated. + */
This is the second time I'm seeing this comment format style. Why? What changed? Mimi
+ if (evm_status == INTEGRITY_FAIL_IMMUTABLE) + return 0; + if (evm_status != INTEGRITY_PASS) integrity_audit_msg(AUDIT_INTEGRITY_METADATA, d_backing_inode(dentry), dentry->d_name.name, "appraise_metadata",