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fca2f191 | 1 | /* |
c0c0989a | 2 | * SPDX-License-Identifier: LGPL-2.1-only |
fca2f191 MJ |
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 saved set-group ID context. |
fca2f191 MJ |
8 | */ |
9 | ||
fca2f191 | 10 | #define _LGPL_SOURCE |
b4051ad8 | 11 | #include <stddef.h> |
fca2f191 MJ |
12 | #include <sys/types.h> |
13 | #include <sys/stat.h> | |
14 | #include <unistd.h> | |
15 | #include <lttng/ust-events.h> | |
16 | #include <lttng/ust-tracer.h> | |
17 | #include <lttng/ringbuffer-config.h> | |
fc80554e MJ |
18 | |
19 | #include "context-internal.h" | |
fca2f191 MJ |
20 | #include "creds.h" |
21 | ||
22 | ||
23 | /* | |
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. | |
32 | */ | |
33 | ||
34 | /* | |
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. | |
37 | */ | |
38 | static gid_t cached_vsgid = INVALID_GID; | |
39 | ||
40 | static | |
41 | gid_t get_vsgid(void) | |
42 | { | |
43 | gid_t vsgid; | |
44 | ||
45 | vsgid = CMM_LOAD_SHARED(cached_vsgid); | |
46 | ||
47 | if (caa_unlikely(vsgid == INVALID_GID)) { | |
48 | gid_t gid, egid, sgid; | |
49 | ||
50 | if (getresgid(&gid, &egid, &sgid) == 0) { | |
51 | vsgid = sgid; | |
52 | CMM_STORE_SHARED(cached_vsgid, vsgid); | |
53 | } | |
54 | } | |
55 | ||
56 | return vsgid; | |
57 | } | |
58 | ||
59 | /* | |
60 | * The vsgid can change on setuid, setreuid and setresuid. | |
61 | */ | |
62 | void lttng_context_vsgid_reset(void) | |
63 | { | |
64 | CMM_STORE_SHARED(cached_vsgid, INVALID_GID); | |
65 | } | |
66 | ||
67 | static | |
68 | size_t vsgid_get_size(struct lttng_ctx_field *field, size_t offset) | |
69 | { | |
70 | size_t size = 0; | |
71 | ||
72 | size += lib_ring_buffer_align(offset, lttng_alignof(gid_t)); | |
73 | size += sizeof(gid_t); | |
74 | return size; | |
75 | } | |
76 | ||
77 | static | |
78 | void vsgid_record(struct lttng_ctx_field *field, | |
79 | struct lttng_ust_lib_ring_buffer_ctx *ctx, | |
80 | struct lttng_channel *chan) | |
81 | { | |
82 | gid_t vsgid; | |
83 | ||
84 | vsgid = get_vsgid(); | |
85 | lib_ring_buffer_align_ctx(ctx, lttng_alignof(vsgid)); | |
86 | chan->ops->event_write(ctx, &vsgid, sizeof(vsgid)); | |
87 | } | |
88 | ||
89 | static | |
90 | void vsgid_get_value(struct lttng_ctx_field *field, | |
91 | struct lttng_ctx_value *value) | |
92 | { | |
93 | value->u.s64 = get_vsgid(); | |
94 | } | |
95 | ||
96 | int lttng_add_vsgid_to_ctx(struct lttng_ctx **ctx) | |
97 | { | |
98 | struct lttng_ctx_field *field; | |
99 | ||
100 | field = lttng_append_context(ctx); | |
101 | if (!field) | |
102 | return -ENOMEM; | |
103 | if (lttng_find_context(*ctx, "vsgid")) { | |
104 | lttng_remove_context_field(ctx, field); | |
105 | return -EEXIST; | |
106 | } | |
107 | field->event_field.name = "vsgid"; | |
108 | field->event_field.type.atype = atype_integer; | |
218deb69 MD |
109 | field->event_field.type.u.integer.size = sizeof(gid_t) * CHAR_BIT; |
110 | field->event_field.type.u.integer.alignment = lttng_alignof(gid_t) * CHAR_BIT; | |
111 | field->event_field.type.u.integer.signedness = lttng_is_signed_type(gid_t); | |
112 | field->event_field.type.u.integer.reverse_byte_order = 0; | |
113 | field->event_field.type.u.integer.base = 10; | |
114 | field->event_field.type.u.integer.encoding = lttng_encode_none; | |
fca2f191 MJ |
115 | field->get_size = vsgid_get_size; |
116 | field->record = vsgid_record; | |
117 | field->get_value = vsgid_get_value; | |
118 | lttng_context_update(*ctx); | |
119 | return 0; | |
120 | } |