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 <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28 #include <lttng/ust-events.h>
  29 #include <lttng/ust-tracer.h>
  30 #include <lttng/ringbuffer-config.h>
  31 #include "creds.h"
  32
  33
  34 /*
  35  * At the kernel level, user IDs and group IDs are a per-thread attribute.
  36  * However, POSIX requires that all threads in a process share the same
  37  * credentials. The NPTL threading implementation handles the POSIX
  38  * requirements by providing wrapper functions for the various system calls
  39  * that change process UIDs and GIDs. These wrapper functions (including those
  40  * for setreuid() and setregid()) employ a signal-based technique to ensure
  41  * that when one thread changes credentials, all of the other threads in the
  42  * process also change their credentials.
  43  */
  44
  45 /*
  46  * We cache the result to ensure we don't trigger a system call for
  47  * each event. User / group IDs are global to the process.
  48  */
  49 static gid_t cached_vgid = INVALID_GID;
  50
  51 static
  52 gid_t get_vgid(void)
  53 {
  54         gid_t vgid;
  55
  56         vgid = CMM_LOAD_SHARED(cached_vgid);
  57
  58         if (caa_unlikely(cached_vgid == (gid_t) -1)) {
  59                 vgid = getgid();
  60                 CMM_STORE_SHARED(cached_vgid, vgid);
  61         }
  62
  63         return vgid;
  64 }
  65
  66 /*
  67  * The vgid can change on setuid, setreuid and setresuid.
  68  */
  69 void lttng_context_vgid_reset(void)
  70 {
  71         CMM_STORE_SHARED(cached_vgid, INVALID_GID);
  72 }
  73
  74 static
  75 size_t vgid_get_size(struct lttng_ctx_field *field, size_t offset)
  76 {
  77         size_t size = 0;
  78
  79         size += lib_ring_buffer_align(offset, lttng_alignof(gid_t));
  80         size += sizeof(gid_t);
  81         return size;
  82 }
  83
  84 static
  85 void vgid_record(struct lttng_ctx_field *field,
  86                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  87                  struct lttng_channel *chan)
  88 {
  89         gid_t vgid;
  90
  91         vgid = get_vgid();
  92         lib_ring_buffer_align_ctx(ctx, lttng_alignof(vgid));
  93         chan->ops->event_write(ctx, &vgid, sizeof(vgid));
  94 }
  95
  96 static
  97 void vgid_get_value(struct lttng_ctx_field *field,
  98                 struct lttng_ctx_value *value)
  99 {
 100         value->u.s64 = get_vgid();
 101 }
 102
 103 int lttng_add_vgid_to_ctx(struct lttng_ctx **ctx)
 104 {
 105         struct lttng_ctx_field *field;
 106
 107         field = lttng_append_context(ctx);
 108         if (!field)
 109                 return -ENOMEM;
 110         if (lttng_find_context(*ctx, "vgid")) {
 111                 lttng_remove_context_field(ctx, field);
 112                 return -EEXIST;
 113         }
 114         field->event_field.name = "vgid";
 115         field->event_field.type.atype = atype_integer;
 116         field->event_field.type.u.basic.integer.size = sizeof(gid_t) * CHAR_BIT;
 117         field->event_field.type.u.basic.integer.alignment = lttng_alignof(gid_t) * CHAR_BIT;
 118         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(gid_t);
 119         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
 120         field->event_field.type.u.basic.integer.base = 10;
 121         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 122         field->get_size = vgid_get_size;
 123         field->record = vgid_record;
 124         field->get_value = vgid_get_value;
 125         lttng_context_update(*ctx);
 126         return 0;
 127 }