liblttng-ust/lttng-context-vgid.c

   1 /*
   2  * lttng-context-vgid.c
   3  *
   4  * LTTng UST namespaced real group ID context.
   5  *
   6  * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  *               2019 Michael Jeanson <mjeanson@efficios.com>
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; only
  12  * version 2.1 of the License.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  */
  23
  24 #define _LGPL_SOURCE
  25 #include <stddef.h>
  26 #include <sys/types.h>
  27 #include <sys/stat.h>
  28 #include <unistd.h>
  29 #include <lttng/ust-events.h>
  30 #include <lttng/ust-tracer.h>
  31 #include <lttng/ringbuffer-config.h>
  32 #include "creds.h"
  33
  34
  35 /*
  36  * At the kernel level, user IDs and group IDs are a per-thread attribute.
  37  * However, POSIX requires that all threads in a process share the same
  38  * credentials. The NPTL threading implementation handles the POSIX
  39  * requirements by providing wrapper functions for the various system calls
  40  * that change process UIDs and GIDs. These wrapper functions (including those
  41  * for setreuid() and setregid()) employ a signal-based technique to ensure
  42  * that when one thread changes credentials, all of the other threads in the
  43  * process also change their credentials.
  44  */
  45
  46 /*
  47  * We cache the result to ensure we don't trigger a system call for
  48  * each event. User / group IDs are global to the process.
  49  */
  50 static gid_t cached_vgid = INVALID_GID;
  51
  52 static
  53 gid_t get_vgid(void)
  54 {
  55         gid_t vgid;
  56
  57         vgid = CMM_LOAD_SHARED(cached_vgid);
  58
  59         if (caa_unlikely(cached_vgid == (gid_t) -1)) {
  60                 vgid = getgid();
  61                 CMM_STORE_SHARED(cached_vgid, vgid);
  62         }
  63
  64         return vgid;
  65 }
  66
  67 /*
  68  * The vgid can change on setuid, setreuid and setresuid.
  69  */
  70 void lttng_context_vgid_reset(void)
  71 {
  72         CMM_STORE_SHARED(cached_vgid, INVALID_GID);
  73 }
  74
  75 static
  76 size_t vgid_get_size(struct lttng_ctx_field *field, size_t offset)
  77 {
  78         size_t size = 0;
  79
  80         size += lib_ring_buffer_align(offset, lttng_alignof(gid_t));
  81         size += sizeof(gid_t);
  82         return size;
  83 }
  84
  85 static
  86 void vgid_record(struct lttng_ctx_field *field,
  87                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  88                  struct lttng_channel *chan)
  89 {
  90         gid_t vgid;
  91
  92         vgid = get_vgid();
  93         lib_ring_buffer_align_ctx(ctx, lttng_alignof(vgid));
  94         chan->ops->event_write(ctx, &vgid, sizeof(vgid));
  95 }
  96
  97 static
  98 void vgid_get_value(struct lttng_ctx_field *field,
  99                 struct lttng_ctx_value *value)
 100 {
 101         value->u.s64 = get_vgid();
 102 }
 103
 104 int lttng_add_vgid_to_ctx(struct lttng_ctx **ctx)
 105 {
 106         struct lttng_ctx_field *field;
 107
 108         field = lttng_append_context(ctx);
 109         if (!field)
 110                 return -ENOMEM;
 111         if (lttng_find_context(*ctx, "vgid")) {
 112                 lttng_remove_context_field(ctx, field);
 113                 return -EEXIST;
 114         }
 115         field->event_field.name = "vgid";
 116         field->event_field.type.atype = atype_integer;
 117         field->event_field.type.u.integer.size = sizeof(gid_t) * CHAR_BIT;
 118         field->event_field.type.u.integer.alignment = lttng_alignof(gid_t) * CHAR_BIT;
 119         field->event_field.type.u.integer.signedness = lttng_is_signed_type(gid_t);
 120         field->event_field.type.u.integer.reverse_byte_order = 0;
 121         field->event_field.type.u.integer.base = 10;
 122         field->event_field.type.u.integer.encoding = lttng_encode_none;
 123         field->get_size = vgid_get_size;
 124         field->record = vgid_record;
 125         field->get_value = vgid_get_value;
 126         lttng_context_update(*ctx);
 127         return 0;
 128 }