fix: redundant decl of channel_destroy (-Wredundant-decls)

[lttng-ust.git] / liblttng-ust / lttng-context-vuid.c

/*
 * SPDX-License-Identifier: LGPL-2.1-only
 *
 * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
 *
 * LTTng UST namespaced real user ID context.
 */

#define _LGPL_SOURCE
#include <limits.h>
#include <stddef.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <lttng/ust-events.h>
#include <lttng/ust-tracer.h>
#include <lttng/ringbuffer-context.h>

#include "context-internal.h"
#include "creds.h"


/*
 * At the kernel level, user IDs and group IDs are a per-thread attribute.
 * However, POSIX requires that all threads in a process share the same
 * credentials. The NPTL threading implementation handles the POSIX
 * requirements by providing wrapper functions for the various system calls
 * that change process UIDs and GIDs. These wrapper functions (including those
 * for setreuid() and setregid()) employ a signal-based technique to ensure
 * that when one thread changes credentials, all of the other threads in the
 * process also change their credentials.
 */

/*
 * We cache the result to ensure we don't trigger a system call for
 * each event. User / group IDs are global to the process.
 */
static uid_t cached_vuid = INVALID_UID;

static
uid_t get_vuid(void)
{
	uid_t vuid;

	vuid = CMM_LOAD_SHARED(cached_vuid);

	if (caa_unlikely(vuid == INVALID_UID)) {
		vuid = getuid();
		CMM_STORE_SHARED(cached_vuid, vuid);
	}

	return vuid;
}

/*
 * The vuid can change on setuid, setreuid and setresuid.
 */
void lttng_context_vuid_reset(void)
{
	CMM_STORE_SHARED(cached_vuid, INVALID_UID);
}

static
size_t vuid_get_size(struct lttng_ust_ctx_field *field, size_t offset)
{
	size_t size = 0;

	size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(uid_t));
	size += sizeof(uid_t);
	return size;
}

static
void vuid_record(struct lttng_ust_ctx_field *field,
		 struct lttng_ust_lib_ring_buffer_ctx *ctx,
		 struct lttng_ust_channel_buffer *chan)
{
	uid_t vuid;

	vuid = get_vuid();
	chan->ops->event_write(ctx, &vuid, sizeof(vuid), lttng_ust_rb_alignof(vuid));
}

static
void vuid_get_value(struct lttng_ust_ctx_field *field,
		struct lttng_ust_ctx_value *value)
{
	value->u.s64 = get_vuid();
}

int lttng_add_vuid_to_ctx(struct lttng_ust_ctx **ctx)
{
	struct lttng_ust_ctx_field *field;
	struct lttng_ust_type_common *type;
	int ret;

	type = lttng_ust_create_type_integer(sizeof(uid_t) * CHAR_BIT,
			lttng_ust_rb_alignof(uid_t) * CHAR_BIT,
			lttng_ust_is_signed_type(uid_t),
			BYTE_ORDER, 10);
	if (!type)
		return -ENOMEM;
	field = lttng_append_context(ctx);
	if (!field) {
		ret = -ENOMEM;
		goto error_context;
	}
	if (lttng_find_context(*ctx, "vuid")) {
		ret = -EEXIST;
		goto error_find_context;
	}
	field->event_field->name = strdup("vuid");
	if (!field->event_field->name) {
		ret = -ENOMEM;
		goto error_name;
	}
	field->event_field->type = type;
	field->get_size = vuid_get_size;
	field->record = vuid_record;
	field->get_value = vuid_get_value;
	lttng_context_update(*ctx);
	return 0;

error_name:
error_find_context:
	lttng_remove_context_field(ctx, field);
error_context:
	lttng_ust_destroy_type(type);
	return ret;
}