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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Roberto Sassu <roberto.sassu@huawei.com>,
        Mimi Zohar <zohar@linux.ibm.com>
Subject: [PATCH 5.8 57/70] evm: Check size of security.evm before using it
Date:   Sat, 31 Oct 2020 12:36:29 +0100
Message-Id: <20201031113502.229354143@linuxfoundation.org>
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From: Roberto Sassu <roberto.sassu@huawei.com>

commit 455b6c9112eff8d249e32ba165742085678a80a4 upstream.

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@vger.kernel.org # 4.19.x
Fixes: 5feeb61183dde ("evm: Allow non-SHA1 digital signatures")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 security/integrity/evm/evm_main.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -181,6 +181,12 @@ static enum integrity_status evm_verify_
 		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,