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fca2f191 MJ |
1 | /* |
2 | * lttng-context-vegid.c | |
3 | * | |
4 | * LTTng UST namespaced effective group ID context. | |
5 | * | |
6 | * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
7 | * 2019 Michael Jeanson <mjeanson@efficios.com> | |
8 | * | |
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. | |
13 | * | |
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. | |
18 | * | |
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 | |
22 | */ | |
23 | ||
24 | #define _LGPL_SOURCE | |
25 | #include <sys/types.h> | |
26 | #include <sys/stat.h> | |
27 | #include <unistd.h> | |
28 | #include <lttng/ust-events.h> | |
29 | #include <lttng/ust-tracer.h> | |
30 | #include <lttng/ringbuffer-config.h> | |
31 | #include "creds.h" | |
32 | ||
33 | ||
34 | /* | |
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. | |
43 | */ | |
44 | ||
45 | /* | |
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. | |
48 | */ | |
49 | static gid_t cached_vegid = INVALID_GID; | |
50 | ||
51 | static | |
52 | gid_t get_vegid(void) | |
53 | { | |
54 | gid_t vegid; | |
55 | ||
56 | vegid = CMM_LOAD_SHARED(cached_vegid); | |
57 | ||
58 | if (caa_unlikely(vegid == INVALID_GID)) { | |
59 | vegid = getegid(); | |
60 | CMM_STORE_SHARED(cached_vegid, vegid); | |
61 | } | |
62 | ||
63 | return vegid; | |
64 | } | |
65 | ||
66 | /* | |
67 | * The vegid can change on setuid, setreuid, setresuid and seteuid. | |
68 | */ | |
69 | void lttng_context_vegid_reset(void) | |
70 | { | |
71 | CMM_STORE_SHARED(cached_vegid, INVALID_GID); | |
72 | } | |
73 | ||
74 | static | |
75 | size_t vegid_get_size(struct lttng_ctx_field *field, size_t offset) | |
76 | { | |
77 | size_t size = 0; | |
78 | ||
79 | size += lib_ring_buffer_align(offset, lttng_alignof(gid_t)); | |
80 | size += sizeof(gid_t); | |
81 | return size; | |
82 | } | |
83 | ||
84 | static | |
85 | void vegid_record(struct lttng_ctx_field *field, | |
86 | struct lttng_ust_lib_ring_buffer_ctx *ctx, | |
87 | struct lttng_channel *chan) | |
88 | { | |
89 | gid_t vegid; | |
90 | ||
91 | vegid = get_vegid(); | |
92 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(vegid)); | |
93 | chan->ops->event_write(ctx, &vegid, sizeof(vegid)); | |
94 | } | |
95 | ||
96 | static | |
97 | void vegid_get_value(struct lttng_ctx_field *field, | |
98 | struct lttng_ctx_value *value) | |
99 | { | |
100 | value->u.s64 = get_vegid(); | |
101 | } | |
102 | ||
103 | int lttng_add_vegid_to_ctx(struct lttng_ctx **ctx) | |
104 | { | |
105 | struct lttng_ctx_field *field; | |
106 | ||
107 | field = lttng_append_context(ctx); | |
108 | if (!field) | |
109 | return -ENOMEM; | |
110 | if (lttng_find_context(*ctx, "vegid")) { | |
111 | lttng_remove_context_field(ctx, field); | |
112 | return -EEXIST; | |
113 | } | |
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); | |
126 | return 0; | |
127 | } |