Fix: pass private data to context callbacks
[lttng-ust.git] / liblttng-ust / lttng-context-vgid.c
CommitLineData
fca2f191 1/*
c0c0989a 2 * SPDX-License-Identifier: LGPL-2.1-only
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3 *
4 * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
c0c0989a 5 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
fca2f191 6 *
c0c0989a 7 * LTTng UST namespaced real group ID context.
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8 */
9
10#define _LGPL_SOURCE
9af5d97a 11#include <limits.h>
b4051ad8 12#include <stddef.h>
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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>
0466ac28 18#include <lttng/ringbuffer-context.h>
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19
20#include "context-internal.h"
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21#include "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 */
39static gid_t cached_vgid = INVALID_GID;
40
41static
42gid_t get_vgid(void)
43{
44 gid_t vgid;
45
46 vgid = CMM_LOAD_SHARED(cached_vgid);
47
48 if (caa_unlikely(cached_vgid == (gid_t) -1)) {
49 vgid = getgid();
50 CMM_STORE_SHARED(cached_vgid, vgid);
51 }
52
53 return vgid;
54}
55
56/*
57 * The vgid can change on setuid, setreuid and setresuid.
58 */
59void lttng_context_vgid_reset(void)
60{
61 CMM_STORE_SHARED(cached_vgid, INVALID_GID);
62}
63
64static
4e48b5d2 65size_t vgid_get_size(void *priv __attribute__((unused)),
2208d8b5 66 size_t offset)
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67{
68 size_t size = 0;
69
dc325c1d 70 size += lttng_ust_lib_ring_buffer_align(offset, lttng_ust_rb_alignof(gid_t));
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71 size += sizeof(gid_t);
72 return size;
73}
74
75static
4e48b5d2 76void vgid_record(void *priv __attribute__((unused)),
fca2f191 77 struct lttng_ust_lib_ring_buffer_ctx *ctx,
e7bc0ef6 78 struct lttng_ust_channel_buffer *chan)
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79{
80 gid_t vgid;
81
82 vgid = get_vgid();
8936b6c0 83 chan->ops->event_write(ctx, &vgid, sizeof(vgid), lttng_ust_rb_alignof(vgid));
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84}
85
86static
4e48b5d2 87void vgid_get_value(void *priv __attribute__((unused)),
daacdbfc 88 struct lttng_ust_ctx_value *value)
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89{
90 value->u.s64 = get_vgid();
91}
92
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93static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field(
94 lttng_ust_static_event_field("vgid",
95 lttng_ust_static_type_integer(sizeof(gid_t) * CHAR_BIT,
96 lttng_ust_rb_alignof(gid_t) * CHAR_BIT,
97 lttng_ust_is_signed_type(gid_t),
98 BYTE_ORDER, 10),
99 false, false),
100 vgid_get_size,
101 vgid_record,
102 vgid_get_value,
103 NULL, NULL);
104
daacdbfc 105int lttng_add_vgid_to_ctx(struct lttng_ust_ctx **ctx)
fca2f191 106{
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107 int ret;
108
4e48b5d2 109 if (lttng_find_context(*ctx, ctx_field->event_field->name)) {
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110 ret = -EEXIST;
111 goto error_find_context;
112 }
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113 ret = lttng_ust_context_append(ctx, ctx_field);
114 if (ret)
115 return ret;
fca2f191 116 return 0;
a084756d 117
a084756d 118error_find_context:
a084756d 119 return ret;
fca2f191 120}
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