Add userspace vuid/vgid contexts

[deliverable/lttng-ust.git] / liblttng-ust / lttng-context-vgid.c

diff --git a/liblttng-ust/lttng-context-vgid.c b/liblttng-ust/lttng-context-vgid.c
new file mode 100644 (file)
index 0000000..7ffaf68
--- /dev/null
+++ b/liblttng-ust/lttng-context-vgid.c
@@ -0,0 +1,127 @@
+/*
+ * lttng-context-vgid.c
+ *
+ * LTTng UST namespaced real group ID context.
+ *
+ * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *               2019 Michael Jeanson <mjeanson@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#define _LGPL_SOURCE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <lttng/ust-events.h>
+#include <lttng/ust-tracer.h>
+#include <lttng/ringbuffer-config.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_vgid = INVALID_GID;
+
+static
+gid_t get_vgid(void)
+{
+       gid_t vgid;
+
+       vgid = CMM_LOAD_SHARED(cached_vgid);
+
+       if (caa_unlikely(cached_vgid == (gid_t) -1)) {
+               vgid = getgid();
+               CMM_STORE_SHARED(cached_vgid, vgid);
+       }
+
+       return vgid;
+}
+
+/*
+ * The vgid can change on setuid, setreuid and setresuid.
+ */
+void lttng_context_vgid_reset(void)
+{
+       CMM_STORE_SHARED(cached_vgid, INVALID_GID);
+}
+
+static
+size_t vgid_get_size(struct lttng_ctx_field *field, size_t offset)
+{
+       size_t size = 0;
+
+       size += lib_ring_buffer_align(offset, lttng_alignof(gid_t));
+       size += sizeof(gid_t);
+       return size;
+}
+
+static
+void vgid_record(struct lttng_ctx_field *field,
+                struct lttng_ust_lib_ring_buffer_ctx *ctx,
+                struct lttng_channel *chan)
+{
+       gid_t vgid;
+
+       vgid = get_vgid();
+       lib_ring_buffer_align_ctx(ctx, lttng_alignof(vgid));
+       chan->ops->event_write(ctx, &vgid, sizeof(vgid));
+}
+
+static
+void vgid_get_value(struct lttng_ctx_field *field,
+               struct lttng_ctx_value *value)
+{
+       value->u.s64 = get_vgid();
+}
+
+int lttng_add_vgid_to_ctx(struct lttng_ctx **ctx)
+{
+       struct lttng_ctx_field *field;
+
+       field = lttng_append_context(ctx);
+       if (!field)
+               return -ENOMEM;
+       if (lttng_find_context(*ctx, "vgid")) {
+               lttng_remove_context_field(ctx, field);
+               return -EEXIST;
+       }
+       field->event_field.name = "vgid";
+       field->event_field.type.atype = atype_integer;
+       field->event_field.type.u.basic.integer.size = sizeof(gid_t) * CHAR_BIT;
+       field->event_field.type.u.basic.integer.alignment = lttng_alignof(gid_t) * CHAR_BIT;
+       field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(gid_t);
+       field->event_field.type.u.basic.integer.reverse_byte_order = 0;
+       field->event_field.type.u.basic.integer.base = 10;
+       field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
+       field->get_size = vgid_get_size;
+       field->record = vgid_record;
+       field->get_value = vgid_get_value;
+       lttng_context_update(*ctx);
+       return 0;
+}