liblttng-ust/lttng-context-vsuid.c

   1 /*
   2  * lttng-context-vsuid.c
   3  *
   4  * LTTng UST namespaced saved set-user 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 <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 uid_t cached_vsuid = INVALID_UID;
  51
  52 static
  53 uid_t get_vsuid(void)
  54 {
  55         uid_t vsuid;
  56
  57         vsuid = CMM_LOAD_SHARED(cached_vsuid);
  58
  59         if (caa_unlikely(vsuid == INVALID_UID)) {
  60                 uid_t uid, euid, suid;
  61
  62                 if (getresuid(&uid, &euid, &suid) == 0) {
  63                         vsuid = suid;
  64                         CMM_STORE_SHARED(cached_vsuid, vsuid);
  65                 }
  66         }
  67
  68         return vsuid;
  69 }
  70
  71 /*
  72  * The vsuid can change on setuid, setreuid and setresuid.
  73  */
  74 void lttng_context_vsuid_reset(void)
  75 {
  76         CMM_STORE_SHARED(cached_vsuid, INVALID_UID);
  77 }
  78
  79 static
  80 size_t vsuid_get_size(struct lttng_ctx_field *field, size_t offset)
  81 {
  82         size_t size = 0;
  83
  84         size += lib_ring_buffer_align(offset, lttng_alignof(uid_t));
  85         size += sizeof(uid_t);
  86         return size;
  87 }
  88
  89 static
  90 void vsuid_record(struct lttng_ctx_field *field,
  91                  struct lttng_ust_lib_ring_buffer_ctx *ctx,
  92                  struct lttng_channel *chan)
  93 {
  94         uid_t vsuid;
  95
  96         vsuid = get_vsuid();
  97         lib_ring_buffer_align_ctx(ctx, lttng_alignof(vsuid));
  98         chan->ops->event_write(ctx, &vsuid, sizeof(vsuid));
  99 }
 100
 101 static
 102 void vsuid_get_value(struct lttng_ctx_field *field,
 103                 struct lttng_ctx_value *value)
 104 {
 105         value->u.s64 = get_vsuid();
 106 }
 107
 108 int lttng_add_vsuid_to_ctx(struct lttng_ctx **ctx)
 109 {
 110         struct lttng_ctx_field *field;
 111
 112         field = lttng_append_context(ctx);
 113         if (!field)
 114                 return -ENOMEM;
 115         if (lttng_find_context(*ctx, "vsuid")) {
 116                 lttng_remove_context_field(ctx, field);
 117                 return -EEXIST;
 118         }
 119         field->event_field.name = "vsuid";
 120         field->event_field.type.atype = atype_integer;
 121         field->event_field.type.u.basic.integer.size = sizeof(uid_t) * CHAR_BIT;
 122         field->event_field.type.u.basic.integer.alignment = lttng_alignof(uid_t) * CHAR_BIT;
 123         field->event_field.type.u.basic.integer.signedness = lttng_is_signed_type(uid_t);
 124         field->event_field.type.u.basic.integer.reverse_byte_order = 0;
 125         field->event_field.type.u.basic.integer.base = 10;
 126         field->event_field.type.u.basic.integer.encoding = lttng_encode_none;
 127         field->get_size = vsuid_get_size;
 128         field->record = vsuid_record;
 129         field->get_value = vsuid_get_value;
 130         lttng_context_update(*ctx);
 131         return 0;
 132 }