2 * lttng-context-vsgid.c
4 * LTTng UST namespaced saved set-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
26 #include <sys/types.h>
29 #include <lttng/ust-events.h>
30 #include <lttng/ust-tracer.h>
31 #include <lttng/ringbuffer-config.h>
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.
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.
50 static gid_t cached_vsgid
= INVALID_GID
;
57 vsgid
= CMM_LOAD_SHARED(cached_vsgid
);
59 if (caa_unlikely(vsgid
== INVALID_GID
)) {
60 gid_t gid
, egid
, sgid
;
62 if (getresgid(&gid
, &egid
, &sgid
) == 0) {
64 CMM_STORE_SHARED(cached_vsgid
, vsgid
);
72 * The vsgid can change on setuid, setreuid and setresuid.
74 void lttng_context_vsgid_reset(void)
76 CMM_STORE_SHARED(cached_vsgid
, INVALID_GID
);
80 size_t vsgid_get_size(struct lttng_ctx_field
*field
, size_t offset
)
84 size
+= lib_ring_buffer_align(offset
, lttng_alignof(gid_t
));
85 size
+= sizeof(gid_t
);
90 void vsgid_record(struct lttng_ctx_field
*field
,
91 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
92 struct lttng_channel
*chan
)
97 lib_ring_buffer_align_ctx(ctx
, lttng_alignof(vsgid
));
98 chan
->ops
->event_write(ctx
, &vsgid
, sizeof(vsgid
));
102 void vsgid_get_value(struct lttng_ctx_field
*field
,
103 struct lttng_ctx_value
*value
)
105 value
->u
.s64
= get_vsgid();
108 int lttng_add_vsgid_to_ctx(struct lttng_ctx
**ctx
)
110 struct lttng_ctx_field
*field
;
112 field
= lttng_append_context(ctx
);
115 if (lttng_find_context(*ctx
, "vsgid")) {
116 lttng_remove_context_field(ctx
, field
);
119 field
->event_field
.name
= "vsgid";
120 field
->event_field
.type
.atype
= atype_integer
;
121 field
->event_field
.type
.u
.integer
.size
= sizeof(gid_t
) * CHAR_BIT
;
122 field
->event_field
.type
.u
.integer
.alignment
= lttng_alignof(gid_t
) * CHAR_BIT
;
123 field
->event_field
.type
.u
.integer
.signedness
= lttng_is_signed_type(gid_t
);
124 field
->event_field
.type
.u
.integer
.reverse_byte_order
= 0;
125 field
->event_field
.type
.u
.integer
.base
= 10;
126 field
->event_field
.type
.u
.integer
.encoding
= lttng_encode_none
;
127 field
->get_size
= vsgid_get_size
;
128 field
->record
= vsgid_record
;
129 field
->get_value
= vsgid_get_value
;
130 lttng_context_update(*ctx
);