2 * SPDX-License-Identifier: LGPL-2.1-only
4 * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
7 * LTTng UST namespaced effective user ID context.
12 #include <sys/types.h>
15 #include <lttng/ust-events.h>
16 #include <lttng/ust-tracer.h>
17 #include <lttng/ringbuffer-context.h>
19 #include "context-internal.h"
24 * At the kernel level, user IDs and group IDs are a per-thread attribute.
25 * However, POSIX requires that all threads in a process share the same
26 * credentials. The NPTL threading implementation handles the POSIX
27 * requirements by providing wrapper functions for the various system calls
28 * that change process UIDs and GIDs. These wrapper functions (including those
29 * for setreuid() and setregid()) employ a signal-based technique to ensure
30 * that when one thread changes credentials, all of the other threads in the
31 * process also change their credentials.
35 * We cache the result to ensure we don't trigger a system call for
36 * each event. User / group IDs are global to the process.
38 static uid_t cached_veuid
= INVALID_UID
;
45 veuid
= CMM_LOAD_SHARED(cached_veuid
);
47 if (caa_unlikely(veuid
== INVALID_UID
)) {
49 CMM_STORE_SHARED(cached_veuid
, veuid
);
56 * The veuid can change on setuid, setreuid, setresuid and seteuid.
58 void lttng_context_veuid_reset(void)
60 CMM_STORE_SHARED(cached_veuid
, INVALID_UID
);
64 size_t veuid_get_size(struct lttng_ust_ctx_field
*field
, size_t offset
)
68 size
+= lib_ring_buffer_align(offset
, lttng_alignof(uid_t
));
69 size
+= sizeof(uid_t
);
74 void veuid_record(struct lttng_ust_ctx_field
*field
,
75 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
76 struct lttng_ust_channel_buffer
*chan
)
81 lib_ring_buffer_align_ctx(ctx
, lttng_alignof(veuid
));
82 chan
->ops
->event_write(ctx
, &veuid
, sizeof(veuid
));
86 void veuid_get_value(struct lttng_ust_ctx_field
*field
,
87 struct lttng_ust_ctx_value
*value
)
89 value
->u
.s64
= get_veuid();
92 int lttng_add_veuid_to_ctx(struct lttng_ust_ctx
**ctx
)
94 struct lttng_ust_ctx_field
*field
;
95 struct lttng_ust_type_common
*type
;
98 type
= lttng_ust_create_type_integer(sizeof(uid_t
) * CHAR_BIT
,
99 lttng_alignof(uid_t
) * CHAR_BIT
,
100 lttng_is_signed_type(uid_t
),
104 field
= lttng_append_context(ctx
);
109 if (lttng_find_context(*ctx
, "veuid")) {
111 goto error_find_context
;
113 field
->event_field
->name
= strdup("veuid");
114 if (!field
->event_field
->name
) {
118 field
->event_field
->type
= type
;
119 field
->get_size
= veuid_get_size
;
120 field
->record
= veuid_record
;
121 field
->get_value
= veuid_get_value
;
122 lttng_context_update(*ctx
);
127 lttng_remove_context_field(ctx
, field
);
129 lttng_ust_destroy_type(type
);