Re: [PATCH v7 27/28] LSM: Add /proc attr entry for full LSM context

From: Casey Schaufler <casey@schaufler-ca.com>
To: Kees Cook <keescook@chromium.org>
Cc: casey.schaufler@intel.com, jmorris@namei.org,
	linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
	john.johansen@canonical.com, penguin-kernel@i-love.sakura.ne.jp,
	paul@paul-moore.com, sds@tycho.nsa.gov
Subject: Re: [PATCH v7 27/28] LSM: Add /proc attr entry for full LSM context
Date: Thu, 8 Aug 2019 17:23:26 -0700	[thread overview]
Message-ID: <8783e3b5-0f44-61b6-5bfd-fe7b8ec524b6@schaufler-ca.com> (raw)
In-Reply-To: <201908081521.E0E7CC8F6@keescook>

On 8/8/2019 3:22 PM, Kees Cook wrote:
> On Wed, Aug 07, 2019 at 12:44:09PM -0700, Casey Schaufler wrote:
>> Add an entry /proc/.../attr/context which displays the full
>> process security "context" in compound format:'
>> 	lsm1\0value\0lsm2\0value\0...
>> This entry is not writable.
>>
>> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
>> ---
>>  fs/proc/base.c      |  1 +
>>  security/security.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 46 insertions(+)
>>
>> diff --git a/fs/proc/base.c b/fs/proc/base.c
>> index 7bf70e041315..79600df5f7a2 100644
>> --- a/fs/proc/base.c
>> +++ b/fs/proc/base.c
>> @@ -2619,6 +2619,7 @@ static const struct pid_entry attr_dir_stuff[] = {
>>  	ATTR(NULL, "keycreate",		0666),
>>  	ATTR(NULL, "sockcreate",	0666),
>>  	ATTR(NULL, "display",		0666),
>> +	ATTR(NULL, "context",		0666),
>>  #ifdef CONFIG_SECURITY_SMACK
>>  	DIR("smack",			0555,
>>  	    proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops),
>> diff --git a/security/security.c b/security/security.c
>> index 0ea7ee27e331..e9f579483d12 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -2046,6 +2046,14 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
>>  				char **value)
>>  {
>>  	struct security_hook_list *hp;
>> +	char *final = NULL;
>> +	char *cp;
>> +	char *tp;
>> +	int rc = 0;
>> +	int finallen = 0;
>> +	int llen;
>> +	int clen;
>> +	int tlen;
>>  	int display = lsm_task_display(current);
>>  	int slot = 0;
>>  
>> @@ -2063,6 +2071,43 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
>>  		return -ENOMEM;
>>  	}
>>  
>> +	if (!strcmp(name, "context")) {
>> +		hlist_for_each_entry(hp, &security_hook_heads.getprocattr,
>> +				     list) {
>> +			rc = hp->hook.getprocattr(p, "current", &cp);
>> +			if (rc == -EINVAL || rc == -ENOPROTOOPT)
>> +				continue;
>> +			if (rc < 0) {
>> +				kfree(final);
>> +				return rc;
>> +			}
>> +			llen = strlen(hp->lsmid->lsm) + 1;
>> +			clen = strlen(cp) + 1;
>> +			tlen = llen + clen;
>> +			if (final)
>> +				tlen += finallen;
>> +			tp = kzalloc(tlen, GFP_KERNEL);
>> +			if (tp == NULL) {
>> +				kfree(cp);
>> +				kfree(final);
>> +				return -ENOMEM;
>> +			}
>> +			if (final)
>> +				memcpy(tp, final, finallen);
>> +			memcpy(tp + finallen, hp->lsmid->lsm, llen);
>> +			memcpy(tp + finallen + llen, cp, clen);
>> +			kfree(cp);
>> +			if (final)
>> +				kfree(final);
>> +			final = tp;
>> +			finallen = tlen;
>> +		}
>> +		if (final == NULL)
>> +			return -EINVAL;
>> +		*value = final;
>> +		return finallen;
>> +	}
> Instead of a copy-paste here, please add a helper for use in both
> places...

I added an append_ctx() helper in the "full" series. I can pull it
back to here.

>
>> +
>>  	hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
>>  		if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
>>  			continue;
>> -- 
>> 2.20.1
>>