[PATCH 26/27] LSM: Add /proc attr entry for full LSM context

[Casey Schaufler]

On 7/29/2019 10:19 AM, Kees Cook wrote:
> On Fri, Jul 26, 2019 at 04:39:22PM -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.
> As this is a new API, would it make sense to make this a bit more
> human readable (i.e. newlines not %NUL)?

With the far reaching discussion about what format would be
acceptable in mind I went with Simon McVittie's suggestion.
Also note that AppArmor includes newline in attr/current,
and this way we can preserve the existing value.
It's compatible with /proc/.../cmdline and easily keesized:

	cat /proc/self/attr/context | tr '\0' '\n'

>  (And if not, please justify the
> reasoning in the commit log).

Good idea.

>
> -Kees
>
>> Signed-off-by: Casey Schaufler <casey at 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 5551c146c035..6a89a6b90cce 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -2057,6 +2057,14 @@ 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;
>>  
>> @@ -2074,6 +2082,43 @@ 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;
>> +	}
>> +
>>  	hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
>>  		if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm))
>>  			continue;
>> -- 
>> 2.20.1
>>