Move all sources to 'src/'

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

diff --git a/src/liblttng-ust/lttng-context-vuid.c b/src/liblttng-ust/lttng-context-vuid.c
new file mode 100644 (file)
index 0000000..775f2cb
--- /dev/null
+++ b/src/liblttng-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;
+}