[PATCH 24/25] LSM: Add /proc attr entry for full LSM context

[Stephen Smalley]

On 12/24/19 6:59 PM, 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.

My takeaway from the earlier exchange with Simon on v12 was that we 
should either define a new LSM hook for /proc/pid/attr/context that is 
guaranteed to return a value in a consistent format with SO_PEERCONTEXT 
or fix AppArmor to return consistent results from its existing 
getprocattr hook (particularly with respect to the newline character).

> 
> Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
> cc: linux-api at vger.kernel.org
> ---
>   fs/proc/base.c      |  1 +
>   security/security.c | 27 +++++++++++++++++++++++++++
>   2 files changed, 28 insertions(+)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 950c200cb9ad..d13c2cf50e4b 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2653,6 +2653,7 @@ 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 80539dfd0245..e94de64e114c 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2099,6 +2099,10 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
>   				char **value)
>   {
>   	struct security_hook_list *hp;
> +	char *final = NULL;
> +	char *cp;
> +	int rc = 0;
> +	int finallen = 0;
>   	int display = lsm_task_display(current);
>   	int slot = 0;
>   
> @@ -2126,6 +2130,29 @@ 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;
> +			}
> +			rc = append_ctx(&final, &finallen, hp->lsmid->lsm,
> +					cp, rc);
> +			if (rc < 0) {
> +				kfree(final);
> +				return rc;
> +			}
> +		}
> +		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;
>