[PATCH 57/58] LSM: Specify which LSM to display

[Casey Schaufler]

Create a new entry "display" in /proc/.../attr for controlling
which LSM security information is displayed for a process.
The name of an active LSM that supplies hooks for human readable
data may be written to "display" to set the value. The name of
the LSM currently in use can be read from "display".

Signed-off-by: Casey Schaufler <casey at schaufler-ca.com>
---
 fs/proc/base.c      |   1 +
 security/security.c | 110 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 109 insertions(+), 2 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ddef482f1334..7bf70e041315 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = {
 	ATTR(NULL, "fscreate",		0666),
 	ATTR(NULL, "keycreate",		0666),
 	ATTR(NULL, "sockcreate",	0666),
+	ATTR(NULL, "display",		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 b05265ec24f0..4af99077572d 100644
--- a/security/security.c
+++ b/security/security.c
@@ -46,7 +46,9 @@ static struct kmem_cache *lsm_file_cache;
 static struct kmem_cache *lsm_inode_cache;
 
 char *lsm_names;
-static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init;
+static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = {
+	.lbs_task = sizeof(struct lsm_one_hooks),
+};
 
 /* Boot-time LSM user choice */
 static __initdata const char *chosen_lsm_order;
@@ -577,6 +579,7 @@ static int lsm_task_alloc(struct task_struct *task)
 	task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL);
 	if (task->security == NULL)
 		return -ENOMEM;
+
 	return 0;
 }
 
@@ -736,7 +739,10 @@ int lsm_superblock_alloc(struct super_block *sb)
 
 #define call_one_int_hook(FUNC, IRC, ...) ({			\
 	int RC = IRC;						\
-	if (lsm_base_one.FUNC.FUNC)				\
+	struct lsm_one_hooks *LOH = current->security;		\
+	if (LOH->FUNC.FUNC)					\
+		RC = LOH->FUNC.FUNC(__VA_ARGS__);		\
+	else if (LOH->lsm == NULL && lsm_base_one.FUNC.FUNC)	\
 		RC = lsm_base_one.FUNC.FUNC(__VA_ARGS__);	\
 	RC;							\
 })
@@ -1569,13 +1575,22 @@ int security_file_open(struct file *file)
 
 int security_task_alloc(struct task_struct *task, unsigned long clone_flags)
 {
+	struct lsm_one_hooks *odisplay = current->security;
+	struct lsm_one_hooks *ndisplay;
 	int rc = lsm_task_alloc(task);
 
 	if (rc)
 		return rc;
+
 	rc = call_int_hook(task_alloc, 0, task, clone_flags);
 	if (unlikely(rc))
 		security_task_free(task);
+	else if (odisplay) {
+		ndisplay = task->security;
+		if (ndisplay)
+			*ndisplay = *odisplay;
+	}
+
 	return rc;
 }
 
@@ -1945,10 +1960,28 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name,
 				char **value)
 {
 	struct security_hook_list *hp;
+	struct lsm_one_hooks *loh = current->security;
+	char *s;
+
+	if (!strcmp(name, "display")) {
+		if (loh->lsm)
+			s = loh->lsm;
+		else if (lsm_base_one.lsm)
+			s = lsm_base_one.lsm;
+		else
+			return -EINVAL;
+
+		*value = kstrdup(s, GFP_KERNEL);
+		if (*value)
+			return strlen(s);
+		return -ENOMEM;
+	}
 
 	hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) {
 		if (lsm != NULL && strcmp(lsm, hp->lsm))
 			continue;
+		if (lsm == NULL && loh->lsm && strcmp(loh->lsm, hp->lsm))
+			continue;
 		return hp->hook.getprocattr(p, name, value);
 	}
 	return -EINVAL;
@@ -1958,10 +1991,83 @@ int security_setprocattr(const char *lsm, const char *name, void *value,
 			 size_t size)
 {
 	struct security_hook_list *hp;
+	struct lsm_one_hooks *loh = current->security;
+	bool found = false;
+	char *s;
+
+	/*
+	 * End the passed name at a newline.
+	 */
+	s = strnchr(value, size, '\n');
+	if (s)
+		*s = '\0';
+
+	if (!strcmp(name, "display")) {
+		union security_list_options secid_to_secctx;
+		union security_list_options secctx_to_secid;
+		union security_list_options socket_getpeersec_stream;
+
+		if (size == 0 || size >= 100)
+			return -EINVAL;
+
+		secid_to_secctx.secid_to_secctx = NULL;
+		hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx,
+				     list) {
+			if (size >= strlen(hp->lsm) &&
+			    !strncmp(value, hp->lsm, size)) {
+				secid_to_secctx = hp->hook;
+				found = true;
+				break;
+			}
+		}
+		secctx_to_secid.secctx_to_secid = NULL;
+		hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid,
+				     list) {
+			if (size >= strlen(hp->lsm) &&
+			    !strncmp(value, hp->lsm, size)) {
+				secctx_to_secid = hp->hook;
+				found = true;
+				break;
+			}
+		}
+		socket_getpeersec_stream.socket_getpeersec_stream = NULL;
+		hlist_for_each_entry(hp,
+				&security_hook_heads.socket_getpeersec_stream,
+				     list) {
+			if (size >= strlen(hp->lsm) &&
+			    !strncmp(value, hp->lsm, size)) {
+				socket_getpeersec_stream = hp->hook;
+				found = true;
+				break;
+			}
+		}
+		if (!found)
+			return -EINVAL;
+
+		/*
+		 * The named lsm is active and supplies one or more
+		 * of the relevant hooks. Switch to it.
+		 */
+		s = kmemdup(value, size + 1, GFP_KERNEL);
+		if (s == NULL)
+			return -ENOMEM;
+		s[size] = '\0';
+
+		if (loh->lsm)
+			kfree(loh->lsm);
+		loh->lsm = s;
+		loh->secid_to_secctx = secid_to_secctx;
+		loh->secctx_to_secid = secctx_to_secid;
+		loh->socket_getpeersec_stream = socket_getpeersec_stream;
+
+		return size;
+	}
 
 	hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) {
 		if (lsm != NULL && strcmp(lsm, hp->lsm))
 			continue;
+		if (lsm == NULL && loh->lsm && strcmp(loh->lsm, hp->lsm))
+			continue;
 		return hp->hook.setprocattr(name, value, size);
 	}
 	return -EINVAL;
-- 
2.19.1