src/lib/lttng-ust/lttng-context-vsuid.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 saved set-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/ust-ringbuffer-context.h>
  19
  20 #include "context-internal.h"
  21 #include "common/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_vsuid = INVALID_UID;
  40
  41 static
  42 uid_t get_vsuid(void)
  43 {
  44         uid_t vsuid;
  45
  46         vsuid = CMM_LOAD_SHARED(cached_vsuid);
  47
  48         if (caa_unlikely(vsuid == INVALID_UID)) {
  49                 uid_t uid, euid, suid;
  50
  51                 if (getresuid(&uid, &euid, &suid) == 0) {
  52                         vsuid = suid;
  53                         CMM_STORE_SHARED(cached_vsuid, vsuid);
  54                 }
  55         }
  56
  57         return vsuid;
  58 }
  59
  60 /*
  61  * The vsuid can change on setuid, setreuid and setresuid.
  62  */
  63 void lttng_context_vsuid_reset(void)
  64 {
  65         CMM_STORE_SHARED(cached_vsuid, INVALID_UID);
  66 }
  67
  68 static
  69 size_t vsuid_get_size(void *priv __attribute__((unused)),
  70                 size_t offset)
  71 {
  72         size_t size = 0;
  73
  74         size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(uid_t));
  75         size += sizeof(uid_t);
  76         return size;
  77 }
  78
  79 static
  80 void vsuid_record(void *priv __attribute__((unused)),
  81                  struct lttng_ust_ring_buffer_ctx *ctx,
  82                  struct lttng_ust_channel_buffer *chan)
  83 {
  84         uid_t vsuid;
  85
  86         vsuid = get_vsuid();
  87         chan->ops->event_write(ctx, &vsuid, sizeof(vsuid), lttng_ust_rb_alignof(vsuid));
  88 }
  89
  90 static
  91 void vsuid_get_value(void *priv __attribute__((unused)),
  92                 struct lttng_ust_ctx_value *value)
  93 {
  94         value->u.s64 = get_vsuid();
  95 }
  96
  97 static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
  98         lttng_ust_static_event_field("vsuid",
  99                 lttng_ust_static_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                                 LTTNG_UST_BYTE_ORDER, 10),
 103                 false, false),
 104         vsuid_get_size,
 105         vsuid_record,
 106         vsuid_get_value,
 107         NULL, NULL);
 108
 109 int lttng_add_vsuid_to_ctx(struct lttng_ust_ctx **ctx)
 110 {
 111         int ret;
 112
 113         if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
 114                 ret = -EEXIST;
 115                 goto error_find_context;
 116         }
 117         ret = lttng_ust_context_append(ctx, ctx_field);
 118         if (ret)
 119                 return ret;
 120         return 0;
 121
 122 error_find_context:
 123         return ret;
 124 }