Move liblttng-ust to 'src/lib/'

[lttng-ust.git] / src / lib / lttng-ust / lttng-context-vegid.c

diff --git a/src/lib/lttng-ust/lttng-context-vegid.c b/src/lib/lttng-ust/lttng-context-vegid.c
new file mode 100644 (file)
index 0000000..97618ce
--- /dev/null
+++ b/src/lib/lttng-ust/lttng-context-vegid.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 effective group 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 gid_t cached_vegid = INVALID_GID;
+
+static
+gid_t get_vegid(void)
+{
+       gid_t vegid;
+
+       vegid = CMM_LOAD_SHARED(cached_vegid);
+
+       if (caa_unlikely(vegid == INVALID_GID)) {
+               vegid = getegid();
+               CMM_STORE_SHARED(cached_vegid, vegid);
+       }
+
+       return vegid;
+}
+
+/*
+ * The vegid can change on setuid, setreuid, setresuid and seteuid.
+ */
+void lttng_context_vegid_reset(void)
+{
+       CMM_STORE_SHARED(cached_vegid, INVALID_GID);
+}
+
+static
+size_t vegid_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(gid_t));
+       size += sizeof(gid_t);
+       return size;
+}
+
+static
+void vegid_record(void *priv __attribute__((unused)),
+                struct lttng_ust_lib_ring_buffer_ctx *ctx,
+                struct lttng_ust_channel_buffer *chan)
+{
+       gid_t vegid;
+
+       vegid = get_vegid();
+       chan->ops->event_write(ctx, &vegid, sizeof(vegid), lttng_ust_rb_alignof(vegid));
+}
+
+static
+void vegid_get_value(void *priv __attribute__((unused)),
+               struct lttng_ust_ctx_value *value)
+{
+       value->u.s64 = get_vegid();
+}
+
+static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
+       lttng_ust_static_event_field("vegid",
+               lttng_ust_static_type_integer(sizeof(gid_t) * CHAR_BIT,
+                               lttng_ust_rb_alignof(gid_t) * CHAR_BIT,
+                               lttng_ust_is_signed_type(gid_t),
+                               BYTE_ORDER, 10),
+               false, false),
+       vegid_get_size,
+       vegid_record,
+       vegid_get_value,
+       NULL, NULL);
+
+int lttng_add_vegid_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;
+}