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0fdd1e2c DG |
1 | /* |
2 | * Copyright (C) 2011 - David Goulet <david.goulet@polymtl.ca> | |
3 | * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> | |
4 | * | |
d14d33bf AM |
5 | * This program is free software; you can redistribute it and/or modify |
6 | * it under the terms of the GNU General Public License, version 2 only, | |
7 | * as published by the Free Software Foundation. | |
0fdd1e2c | 8 | * |
d14d33bf AM |
9 | * This program is distributed in the hope that it will be useful, |
10 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
11 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
12 | * GNU General Public License for more details. | |
0fdd1e2c | 13 | * |
d14d33bf AM |
14 | * You should have received a copy of the GNU General Public License along |
15 | * with this program; if not, write to the Free Software Foundation, Inc., | |
16 | * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. | |
0fdd1e2c DG |
17 | */ |
18 | ||
19 | #define _GNU_SOURCE | |
20 | #include <fcntl.h> | |
21 | #include <limits.h> | |
22 | #include <sys/mman.h> | |
23 | #include <sys/stat.h> | |
24 | #include <sys/types.h> | |
25 | #include <sys/wait.h> | |
26 | #include <unistd.h> | |
27 | #include <urcu.h> | |
28 | ||
db758600 | 29 | #include <common/error.h> |
0fdd1e2c | 30 | |
62d53818 DG |
31 | #include "benchmark.h" |
32 | #include "measures.h" | |
0fdd1e2c DG |
33 | #include "shm.h" |
34 | ||
35 | /* | |
36 | * Using fork to set umask in the child process (not multi-thread safe). We | |
37 | * deal with the shm_open vs ftruncate race (happening when the sessiond owns | |
38 | * the shm and does not let everybody modify it, to ensure safety against | |
39 | * shm_unlink) by simply letting the mmap fail and retrying after a few | |
40 | * seconds. For global shm, everybody has rw access to it until the sessiond | |
41 | * starts. | |
42 | */ | |
43 | static int get_wait_shm(char *shm_path, size_t mmap_size, int global) | |
44 | { | |
45 | int wait_shm_fd, ret; | |
0fdd1e2c DG |
46 | mode_t mode; |
47 | ||
62d53818 DG |
48 | tracepoint(ust_notify_perms_start); |
49 | ||
0fdd1e2c DG |
50 | /* Default permissions */ |
51 | mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP; | |
52 | ||
53 | /* Change owner of the shm path */ | |
54 | if (global) { | |
55 | ret = chown(shm_path, 0, 0); | |
56 | if (ret < 0) { | |
57 | if (errno != ENOENT) { | |
df0f840b | 58 | PERROR("chown wait shm"); |
0fdd1e2c DG |
59 | goto error; |
60 | } | |
61 | } | |
62 | ||
63 | /* | |
64 | * If global session daemon, any application can register so the shm | |
65 | * needs to be set in read-only mode for others. | |
66 | */ | |
67 | mode |= S_IROTH; | |
68 | } else { | |
69 | ret = chown(shm_path, getuid(), getgid()); | |
70 | if (ret < 0) { | |
71 | if (errno != ENOENT) { | |
df0f840b | 72 | PERROR("chown wait shm"); |
0fdd1e2c DG |
73 | goto error; |
74 | } | |
75 | } | |
76 | } | |
77 | ||
78 | /* | |
79 | * Set permissions to the shm even if we did not create the shm. | |
80 | */ | |
81 | ret = chmod(shm_path, mode); | |
82 | if (ret < 0) { | |
83 | if (errno != ENOENT) { | |
df0f840b | 84 | PERROR("chmod wait shm"); |
0fdd1e2c DG |
85 | goto error; |
86 | } | |
87 | } | |
88 | ||
89 | /* | |
7d051034 DG |
90 | * We're alone in a child process, so we can modify the process-wide |
91 | * umask. | |
0fdd1e2c | 92 | */ |
7d051034 | 93 | umask(~mode); |
0fdd1e2c | 94 | |
62d53818 DG |
95 | tracepoint(ust_notify_perms_stop); |
96 | ||
97 | tracepoint(ust_notify_shm_start); | |
7d051034 DG |
98 | /* |
99 | * Try creating shm (or get rw access). We don't do an exclusive open, | |
100 | * because we allow other processes to create+ftruncate it concurrently. | |
101 | */ | |
102 | wait_shm_fd = shm_open(shm_path, O_RDWR | O_CREAT, mode); | |
103 | if (wait_shm_fd < 0) { | |
df0f840b | 104 | PERROR("shm_open wait shm"); |
7d051034 DG |
105 | goto error; |
106 | } | |
0fdd1e2c | 107 | |
7d051034 DG |
108 | ret = ftruncate(wait_shm_fd, mmap_size); |
109 | if (ret < 0) { | |
df0f840b | 110 | PERROR("ftruncate wait shm"); |
7d051034 DG |
111 | exit(EXIT_FAILURE); |
112 | } | |
0fdd1e2c | 113 | |
409a0c56 | 114 | #ifndef __FreeBSD__ |
7d051034 DG |
115 | ret = fchmod(wait_shm_fd, mode); |
116 | if (ret < 0) { | |
df0f840b | 117 | PERROR("fchmod"); |
0fdd1e2c | 118 | exit(EXIT_FAILURE); |
0fdd1e2c | 119 | } |
409a0c56 MD |
120 | #else |
121 | #warning "FreeBSD does not support setting file mode on shm FD. Remember that for secure use, lttng-sessiond should be started before applications linked on lttng-ust." | |
122 | #endif | |
0fdd1e2c | 123 | |
62d53818 DG |
124 | tracepoint(ust_notify_shm_stop); |
125 | ||
0fdd1e2c DG |
126 | DBG("Got the wait shm fd %d", wait_shm_fd); |
127 | ||
128 | return wait_shm_fd; | |
129 | ||
130 | error: | |
131 | DBG("Failing to get the wait shm fd"); | |
132 | ||
133 | return -1; | |
134 | } | |
135 | ||
136 | /* | |
137 | * Return the wait shm mmap for UST application notification. The global | |
138 | * variable is used to indicate if the the session daemon is global | |
139 | * (root:tracing) or running with an unprivileged user. | |
140 | * | |
141 | * This returned value is used by futex_wait_update() in futex.c to WAKE all | |
142 | * waiters which are UST application waiting for a session daemon. | |
143 | */ | |
144 | char *shm_ust_get_mmap(char *shm_path, int global) | |
145 | { | |
146 | size_t mmap_size = sysconf(_SC_PAGE_SIZE); | |
147 | int wait_shm_fd, ret; | |
148 | char *wait_shm_mmap; | |
149 | ||
150 | wait_shm_fd = get_wait_shm(shm_path, mmap_size, global); | |
151 | if (wait_shm_fd < 0) { | |
152 | goto error; | |
153 | } | |
154 | ||
62d53818 DG |
155 | tracepoint(ust_notify_mmap_start); |
156 | ||
0fdd1e2c DG |
157 | wait_shm_mmap = mmap(NULL, mmap_size, PROT_WRITE | PROT_READ, |
158 | MAP_SHARED, wait_shm_fd, 0); | |
7d051034 | 159 | |
62d53818 | 160 | tracepoint(ust_notify_mmap_stop); |
0fdd1e2c DG |
161 | /* close shm fd immediately after taking the mmap reference */ |
162 | ret = close(wait_shm_fd); | |
163 | if (ret) { | |
df0f840b | 164 | PERROR("Error closing fd"); |
0fdd1e2c DG |
165 | } |
166 | ||
167 | if (wait_shm_mmap == MAP_FAILED) { | |
168 | DBG("mmap error (can be caused by race with ust)."); | |
169 | goto error; | |
170 | } | |
171 | ||
172 | return wait_shm_mmap; | |
173 | ||
174 | error: | |
175 | return NULL; | |
176 | } |