| 1 | /* |
| 2 | * SPDX-License-Identifier: LGPL-2.1-only |
| 3 | * |
| 4 | * Copyright (C) 2009-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
| 5 | * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com> |
| 6 | * |
| 7 | * LTTng UST namespaced saved set-group ID context. |
| 8 | */ |
| 9 | |
| 10 | #define _LGPL_SOURCE |
| 11 | #include <limits.h> |
| 12 | #include <stddef.h> |
| 13 | #include <sys/types.h> |
| 14 | #include <sys/stat.h> |
| 15 | #include <unistd.h> |
| 16 | #include <lttng/ust-events.h> |
| 17 | #include <lttng/ust-tracer.h> |
| 18 | #include <lttng/ust-ringbuffer-context.h> |
| 19 | |
| 20 | #include "context-internal.h" |
| 21 | #include "common/creds.h" |
| 22 | |
| 23 | |
| 24 | /* |
| 25 | * At the kernel level, user IDs and group IDs are a per-thread attribute. |
| 26 | * However, POSIX requires that all threads in a process share the same |
| 27 | * credentials. The NPTL threading implementation handles the POSIX |
| 28 | * requirements by providing wrapper functions for the various system calls |
| 29 | * that change process UIDs and GIDs. These wrapper functions (including those |
| 30 | * for setreuid() and setregid()) employ a signal-based technique to ensure |
| 31 | * that when one thread changes credentials, all of the other threads in the |
| 32 | * process also change their credentials. |
| 33 | */ |
| 34 | |
| 35 | /* |
| 36 | * We cache the result to ensure we don't trigger a system call for |
| 37 | * each event. User / group IDs are global to the process. |
| 38 | */ |
| 39 | static gid_t cached_vsgid = INVALID_GID; |
| 40 | |
| 41 | static |
| 42 | gid_t get_vsgid(void) |
| 43 | { |
| 44 | gid_t vsgid; |
| 45 | |
| 46 | vsgid = CMM_LOAD_SHARED(cached_vsgid); |
| 47 | |
| 48 | if (caa_unlikely(vsgid == INVALID_GID)) { |
| 49 | gid_t gid, egid, sgid; |
| 50 | |
| 51 | if (getresgid(&gid, &egid, &sgid) == 0) { |
| 52 | vsgid = sgid; |
| 53 | CMM_STORE_SHARED(cached_vsgid, vsgid); |
| 54 | } |
| 55 | } |
| 56 | |
| 57 | return vsgid; |
| 58 | } |
| 59 | |
| 60 | /* |
| 61 | * The vsgid can change on setuid, setreuid and setresuid. |
| 62 | */ |
| 63 | void lttng_context_vsgid_reset(void) |
| 64 | { |
| 65 | CMM_STORE_SHARED(cached_vsgid, INVALID_GID); |
| 66 | } |
| 67 | |
| 68 | static |
| 69 | size_t vsgid_get_size(void *priv __attribute__((unused)), |
| 70 | struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)), |
| 71 | size_t offset) |
| 72 | { |
| 73 | size_t size = 0; |
| 74 | |
| 75 | size += lttng_ust_ring_buffer_align(offset, lttng_ust_rb_alignof(gid_t)); |
| 76 | size += sizeof(gid_t); |
| 77 | return size; |
| 78 | } |
| 79 | |
| 80 | static |
| 81 | void vsgid_record(void *priv __attribute__((unused)), |
| 82 | struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)), |
| 83 | struct lttng_ust_ring_buffer_ctx *ctx, |
| 84 | struct lttng_ust_channel_buffer *chan) |
| 85 | { |
| 86 | gid_t vsgid; |
| 87 | |
| 88 | vsgid = get_vsgid(); |
| 89 | chan->ops->event_write(ctx, &vsgid, sizeof(vsgid), lttng_ust_rb_alignof(vsgid)); |
| 90 | } |
| 91 | |
| 92 | static |
| 93 | void vsgid_get_value(void *priv __attribute__((unused)), |
| 94 | struct lttng_ust_probe_ctx *probe_ctx __attribute__((unused)), |
| 95 | struct lttng_ust_ctx_value *value) |
| 96 | { |
| 97 | value->u.u64 = get_vsgid(); |
| 98 | } |
| 99 | |
| 100 | static const struct lttng_ust_ctx_field *ctx_field = lttng_ust_static_ctx_field( |
| 101 | lttng_ust_static_event_field("vsgid", |
| 102 | lttng_ust_static_type_integer(sizeof(gid_t) * CHAR_BIT, |
| 103 | lttng_ust_rb_alignof(gid_t) * CHAR_BIT, |
| 104 | lttng_ust_is_signed_type(gid_t), |
| 105 | LTTNG_UST_BYTE_ORDER, 10), |
| 106 | false, false), |
| 107 | vsgid_get_size, |
| 108 | vsgid_record, |
| 109 | vsgid_get_value, |
| 110 | NULL, NULL); |
| 111 | |
| 112 | int lttng_add_vsgid_to_ctx(struct lttng_ust_ctx **ctx) |
| 113 | { |
| 114 | int ret; |
| 115 | |
| 116 | if (lttng_find_context(*ctx, ctx_field->event_field->name)) { |
| 117 | ret = -EEXIST; |
| 118 | goto error_find_context; |
| 119 | } |
| 120 | ret = lttng_ust_context_append(ctx, ctx_field); |
| 121 | if (ret) |
| 122 | return ret; |
| 123 | return 0; |
| 124 | |
| 125 | error_find_context: |
| 126 | return ret; |
| 127 | } |