linux-kernel - [PATCH] EVM: Fix null dereference on xattr when xattr fails to allocate

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Date:   Sun, 27 May 2018 23:55:10 +0100
From:   Colin King <colin.king@...onical.com>
To:     Matthew Garrett <mjg59@...gle.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] EVM: Fix null dereference on xattr when xattr fails to allocate

From: Colin Ian King <colin.king@...onical.com>

In the case where the allocation of xattr fails and xattr is NULL, the
error exit return path via label 'out' will dereference xattr when
kfree'ing xattr-name.  Fix this by only kfree'ing xattr->name and xattr
when xattr is non-null.

Detected by CoverityScan, CID#1469366 ("Dereference after null check")

Fixes: fa516b66a1bf ("EVM: Allow runtime modification of the set of verified xattrs")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 security/integrity/evm/evm_secfs.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
index fb8bc950aceb..cf5cd303d7c0 100644
--- a/security/integrity/evm/evm_secfs.c
+++ b/security/integrity/evm/evm_secfs.c
@@ -253,8 +253,10 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
 out:
 	audit_log_format(ab, " res=%d", err);
 	audit_log_end(ab);
-	kfree(xattr->name);
-	kfree(xattr);
+	if (xattr) {
+		kfree(xattr->name);
+		kfree(xattr);
+	}
 	return err;
 }
 
-- 
2.17.0