[10/13] Add event description implementation.

Commit Message

Dr. Greg July 10, 2023, 10:23 a.m. UTC

The event.c file implements support for packaging the description
of an event into its Context Of Execution (COE) and CELL
identities for subsequent modeling by an internal Trusted
Modeling Agent (TMA) or export to a an external trust
orchestrator and TMA.

The tsem_event_allocate() function is called by every security
event handler that determines that an event is to be modeled,
either generically or explicitly.  For externally modeled
security modeling namespaces the event description is released
after the export of the event is completed.

For internally modeled domains the event description is retained
in order to support retention and surfacing of the security event
descriptions until the security modeling namespace is terminated.

The event description structures are allocated from a TSEM
event description cache named 'tsem_event_cache'.  This cache is
created by an initialization function exported from this file
that is called as part of the TSEM LSM initialization process.

In the case of a security event that acts on a file, ie. is
called with a 'struct file' pointer, one of the components of the
CELL value is a digest of the contents of the file.  This file
uses the integrity_kernel_read() function supplied by the
integrity infrastructure to compute the file digest value using
the cryptographic hash function that has been selected for use by
the security modeling namespace.

In a manner similar to the Integrity Measurement Architecture the
file digest processing functionality needs to temporarily alter
the file mode characteristics if the file is not readable.  The
characteristics are returned to their normal file after reading
of the digest is complete.

The TSEM LSM uses the LSM 'blob' infrastructure to allocate a
TSEM specific inode structure when an inode is allocated.  The
digest value for the value is stored in this structure in order
to eliminate subsequent re-computation of the digest value if the
file has not changed.

The inode 'iversion' value is used to detect changes to an inode
in order to trigger the re-computation of the digest value if the
file has changed.

One of the subtle issues that needs to be addressed is to handle
re-entrancy of the file_open security event hook that is caused
by the integrity_kernel_read() function opening the file.  The
TSEM specific inode structure contains a member that is used to
indicate whether or not a digest is being computed for a file.
The tsem_file_open() event handler checks for the presence of
this flag and allows permission for the open if this flag is
detected.

For IPV6 and IPV6 sockets relevant socket information is
collected to be used in the CELL computation.

For a UNIX domain socket (AF_UNIX) the digest of the pathname for
the socket is used for the CELL value.

Other socket types are generically modeled by computing the
digest of the address field supplied when the socket was created
or bound.

Signed-off-by: Greg Wettstein <[e-mail]>
---
 security/tsem/event.c | 669 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 669 insertions(+)
 create mode 100644 security/tsem/event.c

Patch

diff --git a/security/tsem/event.c b/security/tsem/event.c
new file mode 100644
index 000000000000..2e01702817ca
--- /dev/null
+++ b/security/tsem/event.c
@@ -0,0 +1,669 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright (C) 2023 Enjellic Systems Development, LLC
+ * Author: Dr. Greg Wettstein <[e-mail]>
+ *
+ * This file manages the data structures used to define a security event.
+ */
+
+#include <linux/iversion.h>
+#include <linux/user_namespace.h>
+
+#include "tsem.h"
+#include "../integrity/integrity.h"
+
+static struct kmem_cache *event_cachep;
+
+static void refill_event_magazine(struct work_struct *work)
+{
+	unsigned int index;
+	struct tsem_event *ep;
+	struct tsem_work *ws;
+
+	ws = container_of(work, struct tsem_work, work);
+
+	ep = kmem_cache_zalloc(event_cachep, GFP_KERNEL);
+	if (!ep) {
+		pr_warn("tsem: Cannot refill event magazine.\n");
+		return;
+	}
+
+	spin_lock(&ws->u.ctx->magazine_lock);
+	ws->u.ctx->magazine[ws->index] = ep;
+	clear_bit(ws->index, ws->u.ctx->magazine_index);
+
+	/*
+	 * The following memory barrier is used to cause the magazine
+	 * index to be visible after the refill of the cache slot.
+	 */
+	smp_mb__after_atomic();
+	spin_unlock(&ws->u.ctx->magazine_lock);
+
+	if (index >= ws->u.ctx->magazine_size) {
+		kmem_cache_free(event_cachep, ep);
+		WARN_ONCE(true, "Refilling event magazine with no slots.\n");
+	}
+}
+
+static void get_COE(struct tsem_COE *COE)
+
+{
+	struct user_namespace *ns;
+
+	if (tsem_context(current)->use_current_ns)
+		ns = current_user_ns();
+	else
+		ns = &init_user_ns;
+
+	COE->uid = from_kuid(ns, current_uid());
+	COE->euid = from_kuid(ns, current_euid());
+	COE->suid = from_kuid(ns, current_suid());
+
+	COE->gid = from_kgid(ns, current_gid());
+	COE->egid = from_kgid(ns, current_egid());
+	COE->sgid = from_kgid(ns, current_sgid());
+
+	COE->fsuid = from_kuid(ns, current_fsuid());
+	COE->fsgid = from_kgid(ns, current_fsgid());
+
+	COE->capeff.mask = current_cred()->cap_effective;
+}
+
+static char *get_path(struct file *file)
+{
+	int retn = 0;
+	const char *pathname = NULL;
+	char *path, *pathbuffer = NULL;
+
+	pathbuffer = __getname();
+	if (pathbuffer) {
+		pathname = d_absolute_path(&file->f_path, pathbuffer,
+					   PATH_MAX);
+		if (IS_ERR(pathname)) {
+			__putname(pathbuffer);
+			pathbuffer = NULL;
+			pathname = NULL;
+		}
+	}
+
+	if (pathname)
+		path = kstrdup(pathname, GFP_KERNEL);
+	else
+		path = kstrdup(file->f_path.dentry->d_name.name, GFP_KERNEL);
+	if (!path)
+		retn = -ENOMEM;
+
+	if (pathbuffer)
+		__putname(pathbuffer);
+	if (retn)
+		path = ERR_PTR(retn);
+	return path;
+}
+
+static int add_file_name(struct tsem_event *ep)
+{
+	int retn;
+	SHASH_DESC_ON_STACK(shash, tfm);
+
+	shash->tfm = tsem_digest();
+	retn = crypto_shash_init(shash);
+	if (retn)
+		goto done;
+
+	ep->file.name_length = strlen(ep->pathname);
+	retn = crypto_shash_finup(shash, ep->pathname, ep->file.name_length,
+				  ep->file.name);
+
+ done:
+	return retn;
+}
+
+static struct tsem_inode_digest *find_digest(struct tsem_inode *tsip)
+{
+	struct tsem_inode_digest *digest;
+
+	list_for_each_entry(digest, &tsip->digest_list, list) {
+		if (!strcmp(digest->name, tsem_context(current)->digestname))
+			return digest;
+	}
+
+	return NULL;
+}
+
+static struct tsem_inode_digest *add_digest(struct tsem_context *ctx,
+					    struct tsem_inode *tsip)
+{
+	struct tsem_inode_digest *digest;
+
+	digest = kzalloc(sizeof(*digest), GFP_KERNEL);
+	if (!digest)
+		return NULL;
+
+	digest->name = kstrdup(tsem_context(current)->digestname, GFP_KERNEL);
+	if (!digest->name)
+		return NULL;
+
+	list_add(&digest->list, &tsip->digest_list);
+
+	return digest;
+}
+
+static struct file *open_event_file(struct file *file, unsigned int *status)
+{
+	int flags;
+	struct file *alt_file;
+
+	if (!(file->f_mode & FMODE_CAN_READ)) {
+		file->f_mode |= FMODE_CAN_READ;
+		*status |= 4;
+	}
+	if (file->f_mode & FMODE_READ)
+		return file;
+
+	flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT |
+				  O_NOCTTY | O_EXCL);
+	flags |= O_RDONLY;
+
+	alt_file = dentry_open(&file->f_path, flags, file->f_cred);
+	if (!IS_ERR(alt_file)) {
+		*status |= 1;
+		return alt_file;
+	}
+
+	file->f_flags |= FMODE_READ;
+	*status |= 2;
+	return file;
+}
+
+static int get_file_digest(struct file *file, struct inode *inode,
+			   loff_t size, u8 *digest)
+{
+	u8 *bufr;
+	int retn = 0, rsize;
+	unsigned int open_status = 0;
+	loff_t posn = 0;
+	struct file *read_file;
+	SHASH_DESC_ON_STACK(shash, tfm);
+
+	shash->tfm = tsem_digest();
+	retn = crypto_shash_init(shash);
+	if (retn)
+		goto done;
+
+	bufr = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!bufr) {
+		retn = -ENOMEM;
+		goto done;
+	}
+
+	if (!likely(file->f_op->read || file->f_op->read_iter)) {
+		retn = -EINVAL;
+		goto done;
+	}
+	read_file = open_event_file(file, &open_status);
+
+	while (posn < size) {
+		rsize = integrity_kernel_read(read_file, posn, bufr, 4096);
+		if (rsize < 0) {
+			retn = rsize;
+			break;
+		}
+		if (rsize == 0)
+			break;
+
+		posn += rsize;
+		retn = crypto_shash_update(shash, bufr, rsize);
+		if (retn)
+			break;
+	}
+
+	kfree(bufr);
+	if (!retn)
+		retn = crypto_shash_final(shash, digest);
+
+ done:
+	if (open_status & 1)
+		fput(read_file);
+	if (open_status & 2)
+		file->f_flags &= ~FMODE_READ;
+	if (open_status & 4)
+		file->f_flags &= ~FMODE_CAN_READ;
+	return retn;
+}
+
+static int add_file_digest(struct file *file, struct tsem_file *tfp)
+{
+	int retn = 0;
+	u8 measurement[HASH_MAX_DIGESTSIZE];
+	loff_t size;
+	struct inode *inode;
+	struct tsem_inode *tsip;
+	struct tsem_inode_digest *digest;
+	struct tsem_context *ctx = tsem_context(current);
+
+	inode = file_inode(file);
+	tsip = tsem_inode(inode);
+
+	mutex_lock(&tsip->mutex);
+	if (!ctx->external) {
+		retn = tsem_model_has_pseudonym(tsip, tfp);
+		if (retn < 0)
+			goto done;
+		if (retn) {
+			memcpy(tfp->digest, ctx->zero_digest,
+			       tsem_digestsize());
+			retn = 0;
+			goto done;
+		}
+	}
+
+	size = i_size_read(inode);
+	if (!size) {
+		memcpy(tfp->digest, ctx->zero_digest, tsem_digestsize());
+		goto done;
+	}
+
+	digest = find_digest(tsip);
+
+	if (digest && inode_eq_iversion(inode, digest->version) &&
+	    tsip->status == TSEM_INODE_COLLECTED) {
+		memcpy(tfp->digest, digest->value, tsem_digestsize());
+		goto done;
+	}
+
+	tsip->status = TSEM_INODE_COLLECTING;
+	retn = get_file_digest(file, inode, size, measurement);
+	if (retn) {
+		tsip->status = 0;
+		goto done;
+	}
+
+	if (!digest) {
+		digest = add_digest(ctx, tsip);
+		if (!digest) {
+			retn = -ENOMEM;
+			goto done;
+		}
+	}
+
+	memcpy(tfp->digest, measurement, tsem_digestsize());
+	memcpy(digest->value, measurement, tsem_digestsize());
+	digest->version = inode_query_iversion(inode);
+	tsip->status = TSEM_INODE_COLLECTED;
+
+ done:
+	mutex_unlock(&tsip->mutex);
+	return retn;
+}
+
+static int get_file_cell(struct file *file, struct tsem_event *ep)
+{
+	int retn = 1;
+	struct inode *inode;
+	struct user_namespace *ns;
+
+	inode = file_inode(file);
+	inode_lock(inode);
+
+	ep->pathname = get_path(file);
+	if (IS_ERR(ep->pathname)) {
+		retn = PTR_ERR(ep->pathname);
+		goto done;
+	}
+
+	retn = add_file_name(ep);
+	if (retn)
+		goto done;
+
+	retn = add_file_digest(file, &ep->file);
+	if (retn)
+		goto done;
+
+	if (tsem_context(current)->use_current_ns)
+		ns = current_user_ns();
+	else
+		ns = &init_user_ns;
+
+	ep->file.flags = file->f_flags;
+
+	ep->file.uid = from_kuid(ns, inode->i_uid);
+	ep->file.gid = from_kgid(ns, inode->i_gid);
+	ep->file.mode = inode->i_mode;
+	ep->file.s_magic = inode->i_sb->s_magic;
+	memcpy(ep->file.s_id, inode->i_sb->s_id, sizeof(ep->file.s_id));
+	memcpy(ep->file.s_uuid, inode->i_sb->s_uuid.b,
+	       sizeof(ep->file.s_uuid));
+
+ done:
+	inode_unlock(inode);
+	return retn;
+}
+
+static int get_socket_accept(struct tsem_event *ep)
+{
+	char *p, path[UNIX_PATH_MAX + 1];
+	int size, retn = 0;
+	struct tsem_socket_accept_args *sap = &ep->CELL.socket_accept;
+
+	if (sap->family == AF_INET || sap->family == AF_INET6)
+		return retn;
+
+	if (sap->family != AF_UNIX) {
+		memcpy(sap->u.mapping, tsem_context(current)->zero_digest,
+		       tsem_digestsize());
+		return retn;
+	}
+
+	memset(path, '\0', sizeof(path));
+	p = sap->u.af_unix->addr->name->sun_path;
+	size = sap->u.af_unix->addr->len -
+		offsetof(struct sockaddr_un, sun_path);
+	strncpy(path, p, size);
+	memcpy(sap->u.path, path, sizeof(sap->u.path));
+
+	return retn;
+}
+
+static int get_socket_connect(struct tsem_socket_connect_args *scp)
+{
+	u8 *p;
+	int retn, size;
+	SHASH_DESC_ON_STACK(shash, tfm);
+
+	shash->tfm = tsem_digest();
+	retn = crypto_shash_init(shash);
+	if (retn)
+		goto done;
+
+	p = (u8 *) scp->addr->sa_data;
+	size = scp->addr_len - offsetof(struct sockaddr, sa_data);
+	retn = crypto_shash_digest(shash, p, size, scp->u.mapping);
+
+ done:
+	return retn;
+}
+
+static int get_socket_cell(struct tsem_event *ep)
+
+{
+	int size, retn = 0;
+	struct tsem_socket_connect_args *scp = &ep->CELL.socket_connect;
+
+	scp->family = scp->addr->sa_family;
+
+	switch (scp->family) {
+	case AF_INET:
+		memcpy(&scp->u.ipv4, scp->addr, sizeof(scp->u.ipv4));
+		break;
+	case AF_INET6:
+		memcpy(&scp->u.ipv6, scp->addr, sizeof(scp->u.ipv6));
+		break;
+	case AF_UNIX:
+		memset(scp->u.path, '\0', sizeof(scp->u.path));
+		size = scp->addr_len - offsetof(struct sockaddr_un, sun_path);
+		strncpy(scp->u.path, scp->addr->sa_data, size);
+		break;
+	default:
+		retn = get_socket_connect(scp);
+		break;
+	}
+
+	return retn;
+}
+
+/**
+ * tsem_event_init() - Initialize a security event description structure.
+ * @event: The security event number for which the structure is being
+ *	   initialized.
+ * @params: A pointer to the aggregation structure used to hold the
+ *	    parameters that describe the function.
+ * @locked: A boolean flag used to indicate if the event to be
+ *	    initialized is running in atomic context.
+ *
+ * This function is responsible for allocating and initializing the
+ * primary tsem_event structure and populating it based on the event type.
+ *
+ * Return: This function returns a pointer to the allocated structure which
+ *	   on failure will have an error return code embedded in it.
+ */
+struct tsem_event *tsem_event_init(enum tsem_event_type event,
+				   struct tsem_event_parameters *params,
+				   bool locked)
+{
+	int retn = 0;
+	struct tsem_event *ep = NULL;
+	struct tsem_task *task = tsem_task(current);
+
+	ep = tsem_event_allocate(locked);
+	if (!ep)
+		return ERR_PTR(-ENOMEM);
+
+	ep->event = event;
+	ep->locked = locked;
+	ep->pid = task_pid_nr(current);
+	memcpy(ep->comm, current->comm, sizeof(ep->comm));
+	memcpy(ep->task_id, task->task_id, tsem_digestsize());
+
+	get_COE(&ep->COE);
+	switch (event) {
+	case TSEM_FILE_OPEN:
+	case TSEM_BPRM_SET_CREDS:
+		retn = get_file_cell(params->u.file, ep);
+		break;
+	case TSEM_MMAP_FILE:
+		ep->CELL.mmap_file = *params->u.mmap_file;
+		if (!ep->CELL.mmap_file.anonymous)
+			retn = get_file_cell(ep->CELL.mmap_file.file, ep);
+		break;
+	case TSEM_SOCKET_CREATE:
+		ep->CELL.socket_create = *params->u.socket_create;
+		break;
+	case TSEM_SOCKET_CONNECT:
+	case TSEM_SOCKET_BIND:
+		ep->CELL.socket_connect = *params->u.socket_connect;
+		retn = get_socket_cell(ep);
+		break;
+	case TSEM_SOCKET_ACCEPT:
+		ep->CELL.socket_accept = *params->u.socket_accept;
+		retn = get_socket_accept(ep);
+		break;
+	case TSEM_TASK_KILL:
+		ep->CELL.task_kill = *params->u.task_kill;
+		break;
+	case TSEM_GENERIC_EVENT:
+		ep->CELL.event_type = params->u.event_type;
+		break;
+	default:
+		WARN_ONCE(true, "Unhandled event type: %d\n", event);
+		break;
+	}
+
+	if (retn) {
+		kmem_cache_free(event_cachep, ep);
+		ep = ERR_PTR(retn);
+	} else
+		kref_init(&ep->kref);
+
+	return ep;
+}
+
+/**
+ * tsem_free_event() - Free a security event description.
+ * @ep: A pointer to the security event description that is to be freed.
+ *
+ * This function is responsible for freeing the resources that were
+ * allocated by the tsem_event_allocate() function.
+ */
+static void tsem_event_free(struct kref *kref)
+{
+	struct tsem_event *ep;
+
+	ep = container_of(kref, struct tsem_event, kref);
+	if (ep)
+		kfree(ep->pathname);
+	kmem_cache_free(event_cachep, ep);
+}
+
+/**
+ * tsem_event_put() - Release a referenceto a TSEM event description.
+ *
+ * This function is called each time the use of a TSEM event description
+ * is dropped.
+ */
+void tsem_event_put(struct tsem_event *ep)
+{
+	kref_put(&ep->kref, tsem_event_free);
+}
+
+/**
+ * tsem_event_get() - Obtain a reference to a TSEM event description.
+ *
+ * This function is called on each invocation of the tsem_task_free
+ * function to release one of the references on the TMA modeling
+ * structure.
+ */
+void tsem_event_get(struct tsem_event *ep)
+{
+	kref_get(&ep->kref);
+}
+
+/**
+ * tsem_event_allocate() - Allocate a TSEM event description structure.
+ * @locked: A boolean flag used to indicate if the allocation is being
+ *	    done in atomic context and must be serviced from the
+ *	    pre-allocated event description structures.
+ *
+ * Return: This function returns a pointer to the allocated structure or
+ *	   a NULL pointer in the event of an allocation failure.
+ */
+struct tsem_event *tsem_event_allocate(bool locked)
+{
+	unsigned int index;
+	struct tsem_event *ep = NULL;
+	struct tsem_context *ctx = tsem_context(current);
+
+	if (!locked)
+		return kmem_cache_zalloc(event_cachep, GFP_KERNEL);
+
+	spin_lock(&ctx->magazine_lock);
+	index = find_first_zero_bit(ctx->magazine_index, ctx->magazine_size);
+	if (index < ctx->magazine_size) {
+		ep = ctx->magazine[index];
+		ctx->ws[index].index = index;
+		ctx->ws[index].u.ctx = ctx;
+		set_bit(index, ctx->magazine_index);
+
+		/*
+		 * Similar to the issue noted in the refill_event_magazine()
+		 * function, this barrier is used to cause the consumption
+		 * of the cache entry to become visible.
+
+		 */
+		smp_mb__after_atomic();
+	}
+
+	spin_unlock(&ctx->magazine_lock);
+
+	if (ep) {
+		INIT_WORK(&ctx->ws[index].work, refill_event_magazine);
+		queue_work(system_wq, &ctx->ws[index].work);
+		return ep;
+	}
+
+	pr_warn("tsem: %s in %llu failed event allocation, cache size=%u.\n",
+		current->comm, tsem_context(current)->id, ctx->magazine_size);
+	return NULL;
+}
+
+/**
+ * tsem event_magazine_allocate() - Allocate a TSEM event magazine.
+ * @ctx: A pointer to the modeling context that the magazine is
+ *	 to be allocated for.
+ * @size: The number of entries to be created in the magazine.
+
+ * The security modeling event magazine is an array of tsem_event
+ * structures that are used to service security hooks that are called
+ * in atomic context.  Each modeling domain/namespace has a magazine
+ * allocated to it and this function allocates and initializes the
+ * memory structures needed to manage that magazine.
+
+ * Return: This function returns a value of zero on success and a negative
+ *	   error code on failure.
+ */
+int tsem_event_magazine_allocate(struct tsem_context *ctx, size_t size)
+{
+	unsigned int lp;
+	int retn = -ENOMEM;
+
+	ctx->magazine_size = size;
+
+	spin_lock_init(&ctx->magazine_lock);
+
+	ctx->magazine_index = bitmap_zalloc(ctx->magazine_size, GFP_KERNEL);
+	if (!ctx->magazine_index)
+		return retn;
+
+	ctx->magazine = kcalloc(ctx->magazine_size, sizeof(*ctx->magazine),
+				GFP_KERNEL);
+	if (!ctx->magazine)
+		goto done;
+
+	for (lp = 0; lp < ctx->magazine_size; ++lp) {
+		ctx->magazine[lp] = kmem_cache_zalloc(event_cachep,
+						      GFP_KERNEL);
+		if (!ctx->magazine[lp])
+			goto done;
+	}
+
+	ctx->ws = kcalloc(ctx->magazine_size, sizeof(*ctx->ws), GFP_KERNEL);
+	if (ctx->ws)
+		retn = 0;
+
+ done:
+	if (retn)
+		tsem_event_magazine_free(ctx);
+
+	return retn;
+}
+
+/**
+ * tsem event_magazine_free() - Releases a TSEM event magazine.
+ * @ctx: A pointer to the modeling context whose magazine is to be
+ *	 released.
+ *
+ * The function is used to free the memory that was allocated by
+ * the tsem_event_magazine_allocate() function for a security
+ * modeling context.
+ */
+void tsem_event_magazine_free(struct tsem_context *ctx)
+{
+	unsigned int lp;
+
+	for (lp = 0; lp < ctx->magazine_size; ++lp)
+		kmem_cache_free(event_cachep, ctx->magazine[lp]);
+
+	bitmap_free(ctx->magazine_index);
+	kfree(ctx->ws);
+	kfree(ctx->magazine);
+}
+
+/**
+ * tsem event_cache_init() - Initialize the TSEM event cache.
+ *
+ * This function is called by the TSEM initialization function and sets
+ * up the cache that will be used to allocate tsem_event structures.
+ *
+ * Return: This function returns a value of zero on success and a negative
+ *	   error code on failure.
+ */
+int __init tsem_event_cache_init(void)
+{
+	event_cachep = kmem_cache_create("tsem_event_cache",
+					 sizeof(struct tsem_event), 0,
+					 SLAB_PANIC, 0);
+	if (!event_cachep)
+		return -ENOMEM;
+
+	return 0;
+}