2 * lttng-context-vegid.c
4 * LTTng UST namespaced effective group ID context.
6 * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7 * 2019 Michael Jeanson <mjeanson@efficios.com>
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.
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.
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
25 #include <sys/types.h>
28 #include <lttng/ust-events.h>
29 #include <lttng/ust-tracer.h>
30 #include <lttng/ringbuffer-config.h>
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.
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.
49 static gid_t cached_vegid
= INVALID_GID
;
56 vegid
= CMM_LOAD_SHARED(cached_vegid
);
58 if (caa_unlikely(vegid
== INVALID_GID
)) {
60 CMM_STORE_SHARED(cached_vegid
, vegid
);
67 * The vegid can change on setuid, setreuid, setresuid and seteuid.
69 void lttng_context_vegid_reset(void)
71 CMM_STORE_SHARED(cached_vegid
, INVALID_GID
);
75 size_t vegid_get_size(struct lttng_ctx_field
*field
, size_t offset
)
79 size
+= lib_ring_buffer_align(offset
, lttng_alignof(gid_t
));
80 size
+= sizeof(gid_t
);
85 void vegid_record(struct lttng_ctx_field
*field
,
86 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
87 struct lttng_channel
*chan
)
92 lib_ring_buffer_align_ctx(ctx
, lttng_alignof(vegid
));
93 chan
->ops
->event_write(ctx
, &vegid
, sizeof(vegid
));
97 void vegid_get_value(struct lttng_ctx_field
*field
,
98 struct lttng_ctx_value
*value
)
100 value
->u
.s64
= get_vegid();
103 int lttng_add_vegid_to_ctx(struct lttng_ctx
**ctx
)
105 struct lttng_ctx_field
*field
;
107 field
= lttng_append_context(ctx
);
110 if (lttng_find_context(*ctx
, "vegid")) {
111 lttng_remove_context_field(ctx
, field
);
114 field
->event_field
.name
= "vegid";
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
= vegid_get_size
;
123 field
->record
= vegid_record
;
124 field
->get_value
= vegid_get_value
;
125 lttng_context_update(*ctx
);