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

[Mimi Zohar]

On Sat, 2021-08-14 at 16:27 +0800, Tianxing Zhang wrote:
> 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 at gmail.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;

The IMA audit messages already display pathnames via
audit_log_untrustedstring().  Shouldn't any change be limited to the
ima_policy_read() code path?

thanks,

Mimi