linux-kernel - [PATCH v2 03/12] evm: Check size of security.evm before using it

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Message-ID: <20200904092339.19598-4-roberto.sassu@huawei.com>
Date:   Fri, 4 Sep 2020 11:23:30 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     <zohar@...ux.ibm.com>, <mjg59@...gle.com>
CC:     <linux-integrity@...r.kernel.org>,
        <linux-security-module@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <silviu.vlasceanu@...wei.com>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        <stable@...r.kernel.org>
Subject: [PATCH v2 03/12] evm: Check size of security.evm before using it

This patch checks the size for the EVM_IMA_XATTR_DIGSIG and
EVM_XATTR_PORTABLE_DIGSIG types to ensure that the algorithm is read from
the buffer returned by vfs_getxattr_alloc().

Cc: stable@...r.kernel.org # 4.19.x
Fixes: 5feeb61183dde ("evm: Allow non-SHA1 digital signatures")
Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
---
 security/integrity/evm/evm_main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 0d36259b690d..e4b47759ba1c 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -181,6 +181,12 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 		break;
 	case EVM_IMA_XATTR_DIGSIG:
 	case EVM_XATTR_PORTABLE_DIGSIG:
+		/* accept xattr with non-empty signature field */
+		if (xattr_len <= sizeof(struct signature_v2_hdr)) {
+			evm_status = INTEGRITY_FAIL;
+			goto out;
+		}
+
 		hdr = (struct signature_v2_hdr *)xattr_data;
 		digest.hdr.algo = hdr->hash_algo;
 		rc = evm_calc_hash(dentry, xattr_name, xattr_value,
-- 
2.27.GIT