linux-kernel - Re: [RFC PATCH] ima: verify mprotect change is consistent with mmap policy

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Message-ID: <7812a3a7-f47d-c924-c12e-f417bb6f43dc@linux.microsoft.com>
Date:   Mon, 4 May 2020 15:51:47 -0700
From:   Lakshmi Ramasubramanian <nramas@...ux.microsoft.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>, linux-integrity@...r.kernel.org
Cc:     Jann Horn <jannh@...gle.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Biggers <ebiggers@...nel.org>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ima: verify mprotect change is consistent with mmap
 policy

On 5/4/20 2:17 PM, Mimi Zohar wrote:

Hi Mimi,

> +int ima_file_mprotect(struct vm_area_struct *vma, unsigned long prot)
> +{
> +	struct ima_template_desc *template;
> +	struct inode *inode;
> +	int result = 0;
> +	int action;
> +	u32 secid;
> +	int pcr;
> +
> +	if (vma->vm_file && (prot & PROT_EXEC) && !(vma->vm_flags & VM_EXEC)) {

Just a suggestion:
Maybe you could do the negative of the above check and return, so that 
the block within the if statement doesn't have to be indented.

> +		inode = file_inode(vma->vm_file);
> +
> +		security_task_getsecid(current, &secid);
> +		action = ima_get_action(inode, current_cred(), secid, MAY_EXEC,
> +					MMAP_CHECK, &pcr, &template, 0);
> +
> +		if (action & IMA_APPRAISE_SUBMASK)
> +			result = -EPERM;
> +
> +		if ((action & IMA_APPRAISE_SUBMASK) || (action & IMA_MEASURE)) {

action is checked for IMA_APPRAISE_SUBMASK bits in the previous if 
statement. Does it need to be checked again in the above if statement?

> +			struct file *file = vma->vm_file;
> +			char *pathbuf = NULL;
> +			const char *pathname;
> +			char filename[NAME_MAX];
> +
> +			pathname = ima_d_path(&file->f_path, &pathbuf,
> +					      filename);
> +			integrity_audit_msg(AUDIT_INTEGRITY_DATA, inode,
> +					    pathname, "collect_data",
> +					    "failed-mprotect", result, 0);
> +
> +			if (pathbuf)
> +				__putname(pathbuf);
> +		}
> +	}
> +	return result;
> +}

thanks,
  -lakshmi