liblttng-ust/lttng-context-vsgid.c

   1 /*
   2  * lttng-context-vsgid.c
   3  *
   4  * LTTng UST namespaced saved set-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 _GNU_SOURCE
  25 #define _LGPL_SOURCE
  26 #include <stddef.h>
  27 #include <sys/types.h>
  28 #include <sys/stat.h>
  29 #include <unistd.h>
  30 #include <lttng/ust-events.h>
  31 #include <lttng/ust-tracer.h>
  32 #include <lttng/ringbuffer-config.h>
  33 #include "creds.h"
  34
  35
  36 /*
  37  * At the kernel level, user IDs and group IDs are a per-thread attribute.
  38  * However, POSIX requires that all threads in a process share the same
  39  * credentials. The NPTL threading implementation handles the POSIX
  40  * requirements by providing wrapper functions for the various system calls
  41  * that change process UIDs and GIDs. These wrapper functions (including those
  42  * for setreuid() and setregid()) employ a signal-based technique to ensure
  43  * that when one thread changes credentials, all of the other threads in the
  44  * process also change their credentials.
  45  */
  46
  47 /*
  48  * We cache the result to ensure we don't trigger a system call for
  49  * each event. User / group IDs are global to the process.
  50  */
  51 static gid_t cached_vsgid = INVALID_GID;
  52
  53 static
  54 gid_t get_vsgid(void)
  55 {
  56         gid_t vsgid;
  57
  58         vsgid = CMM_LOAD_SHARED(cached_vsgid);
  59
  60         if (caa_unlikely(vsgid == INVALID_GID)) {
  61                 gid_t gid, egid, sgid;
  62
  63                 if (getresgid(&gid, &egid, &sgid) == 0) {
  64                         vsgid = sgid;
  65                         CMM_STORE_SHARED(cached_vsgid, vsgid);
  66                 }
  67         }
  68
  69         return vsgid;
  70 }
  71
  72 /*
  73  * The vsgid can change on setuid, setreuid and setresuid.
  74  */
  75 void lttng_context_vsgid_reset(void)
  76 {
  77         CMM_STORE_SHARED(cached_vsgid, INVALID_GID);
  78 }
  79
  80 static
  81 size_t vsgid_get_size(struct lttng_ctx_field *field, size_t offset)
  82 {
  83         size_t size = 0;
  84
  85         size += lib_ring_buffer_align(offset, lttng_alignof(gid_t));
  86         size += sizeof(gid_t);
  87         return size;
  88 }
  89
  90 static
  91 void vsgid_record(struct lttng_ctx_field *field,
  92                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  93                  struct lttng_channel *chan)
  94 {
  95         gid_t vsgid;
  96
  97         vsgid = get_vsgid();
  98         lib_ring_buffer_align_ctx(ctx, lttng_alignof(vsgid));
  99         chan->ops->event_write(ctx, &vsgid, sizeof(vsgid));
 100 }
 101
 102 static
 103 void vsgid_get_value(struct lttng_ctx_field *field,
 104                 struct lttng_ctx_value *value)
 105 {
 106         value->u.s64 = get_vsgid();
 107 }
 108
 109 int lttng_add_vsgid_to_ctx(struct lttng_ctx **ctx)
 110 {
 111         struct lttng_ctx_field *field;
 112
 113         field = lttng_append_context(ctx);
 114         if (!field)
 115                 return -ENOMEM;
 116         if (lttng_find_context(*ctx, "vsgid")) {
 117                 lttng_remove_context_field(ctx, field);
 118                 return -EEXIST;
 119         }
 120         field->event_field.name = "vsgid";
 121         field->event_field.type.atype = atype_integer;
 122         field->event_field.type.u.integer.size = sizeof(gid_t) * CHAR_BIT;
 123         field->event_field.type.u.integer.alignment = lttng_alignof(gid_t) * CHAR_BIT;
 124         field->event_field.type.u.integer.signedness = lttng_is_signed_type(gid_t);
 125         field->event_field.type.u.integer.reverse_byte_order = 0;
 126         field->event_field.type.u.integer.base = 10;
 127         field->event_field.type.u.integer.encoding = lttng_encode_none;
 128         field->get_size = vsgid_get_size;
 129         field->record = vsgid_record;
 130         field->get_value = vsgid_get_value;
 131         lttng_context_update(*ctx);
 132         return 0;
 133 }