linux-kernel - [PATCH 1/1] ima: check control characters in policy file path

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Date:   Sat, 14 Aug 2021 16:27:23 +0800
From:   Tianxing Zhang <anakinzhang96@...il.com>
To:     zohar@...ux.ibm.com
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Tianxing Zhang <anakinzhang96@...il.com>
Subject: [PATCH 1/1] ima: check control characters in policy file path

When a policy file path contains control characters like '\r' or '\b',
invalid error messages can be printed to overwrite system messages:

$ echo -e "/\rtest 12345678" > /sys/kernel/security/ima/policy

This patch rejects policy paths with control characters.

Signed-off-by: Tianxing Zhang <anakinzhang96@...il.com>
---
 security/integrity/ima/ima_fs.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
index 3d8e9d5db5aa..e6daa138de89 100644
--- a/security/integrity/ima/ima_fs.c
+++ b/security/integrity/ima/ima_fs.c
@@ -316,6 +316,7 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
 {
 	char *data;
 	ssize_t result;
+	int i;
 
 	if (datalen >= PAGE_SIZE)
 		datalen = PAGE_SIZE - 1;
@@ -331,6 +332,14 @@ static ssize_t ima_write_policy(struct file *file, const char __user *buf,
 		goto out;
 	}
 
+	for (i = 0; data[i] != '\n' && data[i] != '\0'; i++) {
+		if (iscntrl(data[i])) {
+			pr_err_once("file path with no control characters required\n");
+			result = -EINVAL;
+			goto out_free;
+		}
+	}
+
 	result = mutex_lock_interruptible(&ima_write_mutex);
 	if (result < 0)
 		goto out_free;
-- 
2.25.1