liblttng-ust/lttng-context-vuid.c

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
   6  *
   7  * LTTng UST namespaced real user ID context.
   8  */
   9
  10 #define _LGPL_SOURCE
  11 #include <limits.h>
  12 #include <stddef.h>
  13 #include <sys/types.h>
  14 #include <sys/stat.h>
  15 #include <unistd.h>
  16 #include <lttng/ust-events.h>
  17 #include <lttng/ust-tracer.h>
  18 #include <lttng/ringbuffer-context.h>
  19
  20 #include "context-internal.h"
  21 #include "creds.h"
  22
  23
  24 /*
  25  * At the kernel level, user IDs and group IDs are a per-thread attribute.
  26  * However, POSIX requires that all threads in a process share the same
  27  * credentials. The NPTL threading implementation handles the POSIX
  28  * requirements by providing wrapper functions for the various system calls
  29  * that change process UIDs and GIDs. These wrapper functions (including those
  30  * for setreuid() and setregid()) employ a signal-based technique to ensure
  31  * that when one thread changes credentials, all of the other threads in the
  32  * process also change their credentials.
  33  */
  34
  35 /*
  36  * We cache the result to ensure we don't trigger a system call for
  37  * each event. User / group IDs are global to the process.
  38  */
  39 static uid_t cached_vuid = INVALID_UID;
  40
  41 static
  42 uid_t get_vuid(void)
  43 {
  44         uid_t vuid;
  45
  46         vuid = CMM_LOAD_SHARED(cached_vuid);
  47
  48         if (caa_unlikely(vuid == INVALID_UID)) {
  49                 vuid = getuid();
  50                 CMM_STORE_SHARED(cached_vuid, vuid);
  51         }
  52
  53         return vuid;
  54 }
  55
  56 /*
  57  * The vuid can change on setuid, setreuid and setresuid.
  58  */
  59 void lttng_context_vuid_reset(void)
  60 {
  61         CMM_STORE_SHARED(cached_vuid, INVALID_UID);
  62 }
  63
  64 static
  65 size_t vuid_get_size(struct lttng_ust_ctx_field *field, size_t offset)
  66 {
  67         size_t size = 0;
  68
  69         size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(uid_t));
  70         size += sizeof(uid_t);
  71         return size;
  72 }
  73
  74 static
  75 void vuid_record(struct lttng_ust_ctx_field *field,
  76                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  77                  struct lttng_ust_channel_buffer *chan)
  78 {
  79         uid_t vuid;
  80
  81         vuid = get_vuid();
  82         lttng_ust_lib_ring_buffer_align_ctx(ctx, lttng_ust_rb_alignof(vuid));
  83         chan->ops->event_write(ctx, &vuid, sizeof(vuid));
  84 }
  85
  86 static
  87 void vuid_get_value(struct lttng_ust_ctx_field *field,
  88                 struct lttng_ust_ctx_value *value)
  89 {
  90         value->u.s64 = get_vuid();
  91 }
  92
  93 int lttng_add_vuid_to_ctx(struct lttng_ust_ctx **ctx)
  94 {
  95         struct lttng_ust_ctx_field *field;
  96         struct lttng_ust_type_common *type;
  97         int ret;
  98
  99         type = lttng_ust_create_type_integer(sizeof(uid_t) * CHAR_BIT,
 100                         lttng_ust_rb_alignof(uid_t) * CHAR_BIT,
 101                         lttng_ust_is_signed_type(uid_t),
 102                         BYTE_ORDER, 10);
 103         if (!type)
 104                 return -ENOMEM;
 105         field = lttng_append_context(ctx);
 106         if (!field) {
 107                 ret = -ENOMEM;
 108                 goto error_context;
 109         }
 110         if (lttng_find_context(*ctx, "vuid")) {
 111                 ret = -EEXIST;
 112                 goto error_find_context;
 113         }
 114         field->event_field->name = strdup("vuid");
 115         if (!field->event_field->name) {
 116                 ret = -ENOMEM;
 117                 goto error_name;
 118         }
 119         field->event_field->type = type;
 120         field->get_size = vuid_get_size;
 121         field->record = vuid_record;
 122         field->get_value = vuid_get_value;
 123         lttng_context_update(*ctx);
 124         return 0;
 125
 126 error_name:
 127 error_find_context:
 128         lttng_remove_context_field(ctx, field);
 129 error_context:
 130         lttng_ust_destroy_type(type);
 131         return ret;
 132 }