Commit | Line | Data |
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0fdd1e2c | 1 | /* |
90c106c6 | 2 | * Copyright (C) 2011 EfficiOS Inc. |
ab5be9fa | 3 | * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
0fdd1e2c | 4 | * |
ab5be9fa | 5 | * SPDX-License-Identifier: GPL-2.0-only |
0fdd1e2c | 6 | * |
0fdd1e2c DG |
7 | */ |
8 | ||
6c1c0768 | 9 | #define _LGPL_SOURCE |
0fdd1e2c DG |
10 | #include <fcntl.h> |
11 | #include <limits.h> | |
12 | #include <sys/mman.h> | |
13 | #include <sys/stat.h> | |
14 | #include <sys/types.h> | |
15 | #include <sys/wait.h> | |
16 | #include <unistd.h> | |
17 | #include <urcu.h> | |
18 | ||
db758600 | 19 | #include <common/error.h> |
0fdd1e2c DG |
20 | |
21 | #include "shm.h" | |
22 | ||
23 | /* | |
0f8f94b1 | 24 | * We deal with the shm_open vs ftruncate race (happening when the sessiond owns |
0fdd1e2c DG |
25 | * the shm and does not let everybody modify it, to ensure safety against |
26 | * shm_unlink) by simply letting the mmap fail and retrying after a few | |
27 | * seconds. For global shm, everybody has rw access to it until the sessiond | |
28 | * starts. | |
29 | */ | |
30 | static int get_wait_shm(char *shm_path, size_t mmap_size, int global) | |
31 | { | |
32 | int wait_shm_fd, ret; | |
0f8f94b1 | 33 | mode_t mode, old_mode; |
0fdd1e2c | 34 | |
0525e9ae DG |
35 | assert(shm_path); |
36 | ||
0fdd1e2c DG |
37 | /* Default permissions */ |
38 | mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP; | |
39 | ||
7972d619 DG |
40 | /* |
41 | * Change owner of the shm path. | |
42 | */ | |
0fdd1e2c | 43 | if (global) { |
0fdd1e2c | 44 | /* |
7972d619 DG |
45 | * If global session daemon, any application can |
46 | * register. Make it initially writeable so applications | |
47 | * registering concurrently can do ftruncate() by | |
48 | * themselves. | |
0fdd1e2c | 49 | */ |
7972d619 | 50 | mode |= S_IROTH | S_IWOTH; |
0fdd1e2c DG |
51 | } |
52 | ||
0f8f94b1 | 53 | old_mode = umask(~mode); |
0fdd1e2c | 54 | |
7d051034 DG |
55 | /* |
56 | * Try creating shm (or get rw access). We don't do an exclusive open, | |
57 | * because we allow other processes to create+ftruncate it concurrently. | |
cf86ff2c JG |
58 | * |
59 | * A sysctl, fs.protected_regular may prevent the session daemon from | |
60 | * opening a previously created shm when the O_CREAT flag is provided. | |
61 | * Systemd enables this ABI-breaking change by default since v241. | |
62 | * | |
63 | * First, attempt to use the create-or-open semantic that is | |
64 | * desired here. If this fails with EACCES, work around this broken | |
65 | * behaviour and attempt to open the shm without the O_CREAT flag. | |
66 | * | |
67 | * The two attempts are made in this order since applications are | |
68 | * expected to race with the session daemon to create this shm. | |
69 | * Attempting an shm_open() without the O_CREAT flag first could fail | |
70 | * because the file doesn't exist. It could then be created by an | |
71 | * application, which would cause a second try with the O_CREAT flag to | |
72 | * fail with EACCES. | |
73 | * | |
74 | * Note that this introduces a new failure mode where a user could | |
75 | * launch an application (creating the shm) and unlink the shm while | |
76 | * the session daemon is launching, causing the second attempt | |
77 | * to fail. This is not recovered-from as unlinking the shm will | |
78 | * prevent userspace tracing from succeeding anyhow: the sessiond would | |
79 | * use a now-unlinked shm, while the next application would create | |
80 | * a new named shm. | |
7d051034 DG |
81 | */ |
82 | wait_shm_fd = shm_open(shm_path, O_RDWR | O_CREAT, mode); | |
83 | if (wait_shm_fd < 0) { | |
cf86ff2c JG |
84 | if (errno == EACCES) { |
85 | /* Work around sysctl fs.protected_regular. */ | |
86 | DBG("shm_open of %s returned EACCES, this may be caused " | |
87 | "by the fs.protected_regular sysctl. " | |
88 | "Attempting to open the shm without " | |
89 | "creating it.", shm_path); | |
90 | wait_shm_fd = shm_open(shm_path, O_RDWR, mode); | |
91 | } | |
92 | if (wait_shm_fd < 0) { | |
6c33300e | 93 | PERROR("Failed to open \"wait\" shared memory object: path = '%s'", shm_path); |
cf86ff2c JG |
94 | goto error; |
95 | } | |
7d051034 | 96 | } |
0fdd1e2c | 97 | |
7d051034 DG |
98 | ret = ftruncate(wait_shm_fd, mmap_size); |
99 | if (ret < 0) { | |
6c33300e JG |
100 | PERROR("Failed to truncate \"wait\" shared memory object: fd = %d, size = %zu", |
101 | wait_shm_fd, mmap_size); | |
0f8f94b1 | 102 | goto error; |
7d051034 | 103 | } |
0fdd1e2c | 104 | |
7972d619 DG |
105 | if (global) { |
106 | ret = fchown(wait_shm_fd, 0, 0); | |
107 | if (ret < 0) { | |
6c33300e JG |
108 | PERROR("Failed to set ownership of \"wait\" shared memory object: fd = %d, owner = 0, group = 0", |
109 | wait_shm_fd); | |
0f8f94b1 | 110 | goto error; |
7972d619 DG |
111 | } |
112 | /* | |
113 | * If global session daemon, any application can | |
114 | * register so the shm needs to be set in read-only mode | |
115 | * for others. | |
116 | */ | |
117 | mode &= ~S_IWOTH; | |
118 | ret = fchmod(wait_shm_fd, mode); | |
119 | if (ret < 0) { | |
6c33300e JG |
120 | PERROR("Failed to set the mode of the \"wait\" shared memory object: fd = %d, mode = %d", |
121 | wait_shm_fd, mode); | |
0f8f94b1 | 122 | goto error; |
7972d619 DG |
123 | } |
124 | } else { | |
125 | ret = fchown(wait_shm_fd, getuid(), getgid()); | |
126 | if (ret < 0) { | |
6c33300e JG |
127 | PERROR("Failed to set ownership of \"wait\" shared memory object: fd = %d, owner = %d, group = %d", |
128 | wait_shm_fd, getuid(), getgid()); | |
0f8f94b1 | 129 | goto error; |
7972d619 | 130 | } |
0fdd1e2c DG |
131 | } |
132 | ||
6c33300e JG |
133 | DBG("Wait shared memory file descriptor created successfully: path = '%s', mmap_size = %zu, global = %s, fd = %d", |
134 | shm_path, mmap_size, global ? "true" : "false", | |
135 | wait_shm_fd); | |
0fdd1e2c | 136 | |
0f8f94b1 JR |
137 | end: |
138 | (void) umask(old_mode); | |
0fdd1e2c DG |
139 | return wait_shm_fd; |
140 | ||
141 | error: | |
0f8f94b1 JR |
142 | DBG("Failing to get the wait shm fd"); |
143 | if (wait_shm_fd >= 0) { | |
144 | if (close(wait_shm_fd)) { | |
145 | PERROR("Failed to close wait shm file descriptor during error handling"); | |
146 | } | |
147 | } | |
0fdd1e2c | 148 | |
0f8f94b1 JR |
149 | wait_shm_fd = -1; |
150 | goto end; | |
0fdd1e2c DG |
151 | } |
152 | ||
153 | /* | |
154 | * Return the wait shm mmap for UST application notification. The global | |
155 | * variable is used to indicate if the the session daemon is global | |
156 | * (root:tracing) or running with an unprivileged user. | |
157 | * | |
158 | * This returned value is used by futex_wait_update() in futex.c to WAKE all | |
159 | * waiters which are UST application waiting for a session daemon. | |
160 | */ | |
5779a467 | 161 | LTTNG_HIDDEN |
0fdd1e2c DG |
162 | char *shm_ust_get_mmap(char *shm_path, int global) |
163 | { | |
6c699394 | 164 | size_t mmap_size; |
0fdd1e2c DG |
165 | int wait_shm_fd, ret; |
166 | char *wait_shm_mmap; | |
6c699394 | 167 | long sys_page_size; |
0fdd1e2c | 168 | |
0525e9ae DG |
169 | assert(shm_path); |
170 | ||
6c699394 DG |
171 | sys_page_size = sysconf(_SC_PAGE_SIZE); |
172 | if (sys_page_size < 0) { | |
6c33300e | 173 | PERROR("Failed to get PAGE_SIZE of system"); |
6c699394 DG |
174 | goto error; |
175 | } | |
176 | mmap_size = sys_page_size; | |
177 | ||
0fdd1e2c DG |
178 | wait_shm_fd = get_wait_shm(shm_path, mmap_size, global); |
179 | if (wait_shm_fd < 0) { | |
180 | goto error; | |
181 | } | |
182 | ||
183 | wait_shm_mmap = mmap(NULL, mmap_size, PROT_WRITE | PROT_READ, | |
184 | MAP_SHARED, wait_shm_fd, 0); | |
7d051034 | 185 | |
0fdd1e2c DG |
186 | /* close shm fd immediately after taking the mmap reference */ |
187 | ret = close(wait_shm_fd); | |
188 | if (ret) { | |
6c33300e JG |
189 | PERROR("Failed to close \"wait\" shared memory object file descriptor: fd = %d", |
190 | wait_shm_fd); | |
0fdd1e2c DG |
191 | } |
192 | ||
193 | if (wait_shm_mmap == MAP_FAILED) { | |
6c33300e JG |
194 | DBG("Failed to mmap the \"wait\" shareed memory object (can be caused by race with ust): path = '%s', global = %s", |
195 | shm_path, global ? "true" : "false"); | |
0fdd1e2c DG |
196 | goto error; |
197 | } | |
198 | ||
199 | return wait_shm_mmap; | |
200 | ||
201 | error: | |
202 | return NULL; | |
203 | } | |
b7fc068d FD |
204 | |
205 | /* | |
206 | * shm_create_anonymous is never called concurrently within a process. | |
207 | */ | |
5779a467 | 208 | LTTNG_HIDDEN |
b7fc068d FD |
209 | int shm_create_anonymous(const char *owner_name) |
210 | { | |
211 | char tmp_name[NAME_MAX]; | |
212 | int shmfd, ret; | |
213 | ||
214 | ret = snprintf(tmp_name, NAME_MAX, "/shm-%s-%d", owner_name, getpid()); | |
215 | if (ret < 0) { | |
6c33300e JG |
216 | PERROR("Failed to format shm path: owner_name = '%s', pid = %d", |
217 | owner_name, getpid()); | |
b7fc068d FD |
218 | return -1; |
219 | } | |
6c33300e | 220 | |
b7fc068d FD |
221 | /* |
222 | * Allocate shm, and immediately unlink its shm oject, keeping only the | |
223 | * file descriptor as a reference to the object. | |
224 | */ | |
225 | shmfd = shm_open(tmp_name, O_CREAT | O_EXCL | O_RDWR, 0700); | |
226 | if (shmfd < 0) { | |
6c33300e | 227 | PERROR("Failed to open shared memory object: path = '%s'", tmp_name); |
b7fc068d FD |
228 | goto error_shm_open; |
229 | } | |
6c33300e | 230 | |
b7fc068d FD |
231 | ret = shm_unlink(tmp_name); |
232 | if (ret < 0 && errno != ENOENT) { | |
6c33300e JG |
233 | PERROR("Failed to unlink shared memory object: path = '%s'", |
234 | tmp_name); | |
b7fc068d FD |
235 | goto error_shm_release; |
236 | } | |
6c33300e | 237 | |
b7fc068d FD |
238 | return shmfd; |
239 | ||
240 | error_shm_release: | |
241 | ret = close(shmfd); | |
242 | if (ret) { | |
6c33300e JG |
243 | PERROR("Failed to close shared memory object file descriptor: fd = %d, path = '%s'", |
244 | shmfd, tmp_name); | |
b7fc068d FD |
245 | } |
246 | error_shm_open: | |
247 | return -1; | |
248 | } |