X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;f=src%2Flib%2Flttng-ust%2Flttng-context-vuid.c;fp=src%2Flib%2Flttng-ust%2Flttng-context-vuid.c;h=775f2cbf5f32f132eab22bc3e59c5b6e23c36e6b;hb=6339062a5bbe886493d0691d13e28e37a7206362;hp=0000000000000000000000000000000000000000;hpb=635ead38ff3308bd6475f088d6a58e6267e53d86;p=lttng-ust.git

diff --git a/src/lib/lttng-ust/lttng-context-vuid.c b/src/lib/lttng-ust/lttng-context-vuid.c
new file mode 100644
index 00000000..775f2cbf
--- /dev/null
+++ b/src/lib/lttng-ust/lttng-context-vuid.c
@@ -0,0 +1,120 @@
+/*
+ * 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(void *priv __attribute__((unused)),
+		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(void *priv __attribute__((unused)),
+		 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(void *priv __attribute__((unused)),
+		struct lttng_ust_ctx_value *value)
+{
+	value->u.s64 = get_vuid();
+}
+
+static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
+	lttng_ust_static_event_field("vuid",
+		lttng_ust_static_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),
+		false, false),
+	vuid_get_size,
+	vuid_record,
+	vuid_get_value,
+	NULL, NULL);
+
+int lttng_add_vuid_to_ctx(struct lttng_ust_ctx **ctx)
+{
+	int ret;
+
+	if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
+		ret = -EEXIST;
+		goto error_find_context;
+	}
+	ret = lttng_ust_context_append(ctx, ctx_field);
+	if (ret)
+		return ret;
+	return 0;
+
+error_find_context:
+	return ret;
+}