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Linux/tools/testing/selftests/proc/fd-003-kthread.c

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  1 /*
  2  * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
  3  *
  4  * Permission to use, copy, modify, and distribute this software for any
  5  * purpose with or without fee is hereby granted, provided that the above
  6  * copyright notice and this permission notice appear in all copies.
  7  *
  8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 11  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 13  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 14  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 15  */
 16 // Test that /proc/$KERNEL_THREAD/fd/ is empty.
 17 
 18 #undef NDEBUG
 19 #include <sys/syscall.h>
 20 #include <assert.h>
 21 #include <dirent.h>
 22 #include <limits.h>
 23 #include <stdio.h>
 24 #include <string.h>
 25 #include <sys/types.h>
 26 #include <sys/stat.h>
 27 #include <fcntl.h>
 28 #include <unistd.h>
 29 
 30 #include "proc.h"
 31 
 32 #define PF_KHTREAD 0x00200000
 33 
 34 /*
 35  * Test for kernel threadness atomically with openat().
 36  *
 37  * Return /proc/$PID/fd descriptor if process is kernel thread.
 38  * Return -1 if a process is userspace process.
 39  */
 40 static int kernel_thread_fd(unsigned int pid)
 41 {
 42         unsigned int flags = 0;
 43         char buf[4096];
 44         int dir_fd, fd;
 45         ssize_t rv;
 46 
 47         snprintf(buf, sizeof(buf), "/proc/%u", pid);
 48         dir_fd = open(buf, O_RDONLY|O_DIRECTORY);
 49         if (dir_fd == -1)
 50                 return -1;
 51 
 52         /*
 53          * Believe it or not, struct task_struct::flags is directly exposed
 54          * to userspace!
 55          */
 56         fd = openat(dir_fd, "stat", O_RDONLY);
 57         if (fd == -1) {
 58                 close(dir_fd);
 59                 return -1;
 60         }
 61         rv = read(fd, buf, sizeof(buf));
 62         close(fd);
 63         if (0 < rv && rv <= sizeof(buf)) {
 64                 unsigned long long flags_ull;
 65                 char *p, *end;
 66                 int i;
 67 
 68                 assert(buf[rv - 1] == '\n');
 69                 buf[rv - 1] = '\0';
 70 
 71                 /* Search backwards: ->comm can contain whitespace and ')'. */
 72                 for (i = 0; i < 43; i++) {
 73                         p = strrchr(buf, ' ');
 74                         assert(p);
 75                         *p = '\0';
 76                 }
 77 
 78                 p = strrchr(buf, ' ');
 79                 assert(p);
 80 
 81                 flags_ull = xstrtoull(p + 1, &end);
 82                 assert(*end == '\0');
 83                 assert(flags_ull == (unsigned int)flags_ull);
 84 
 85                 flags = flags_ull;
 86         }
 87 
 88         fd = -1;
 89         if (flags & PF_KHTREAD) {
 90                 fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);
 91         }
 92         close(dir_fd);
 93         return fd;
 94 }
 95 
 96 static void test_readdir(int fd)
 97 {
 98         DIR *d;
 99         struct dirent *de;
100 
101         d = fdopendir(fd);
102         assert(d);
103 
104         de = xreaddir(d);
105         assert(streq(de->d_name, "."));
106         assert(de->d_type == DT_DIR);
107 
108         de = xreaddir(d);
109         assert(streq(de->d_name, ".."));
110         assert(de->d_type == DT_DIR);
111 
112         de = xreaddir(d);
113         assert(!de);
114 }
115 
116 static inline int sys_statx(int dirfd, const char *pathname, int flags,
117                             unsigned int mask, void *stx)
118 {
119         return syscall(SYS_statx, dirfd, pathname, flags, mask, stx);
120 }
121 
122 static void test_lookup_fail(int fd, const char *pathname)
123 {
124         char stx[256] __attribute__((aligned(8)));
125         int rv;
126 
127         rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx);
128         assert(rv == -1 && errno == ENOENT);
129 }
130 
131 static void test_lookup(int fd)
132 {
133         char buf[64];
134         unsigned int u;
135         int i;
136 
137         for (i = INT_MIN; i < INT_MIN + 1024; i++) {
138                 snprintf(buf, sizeof(buf), "%d", i);
139                 test_lookup_fail(fd, buf);
140         }
141         for (i = -1024; i < 1024; i++) {
142                 snprintf(buf, sizeof(buf), "%d", i);
143                 test_lookup_fail(fd, buf);
144         }
145         for (u = INT_MAX - 1024; u < (unsigned int)INT_MAX + 1024; u++) {
146                 snprintf(buf, sizeof(buf), "%u", u);
147                 test_lookup_fail(fd, buf);
148         }
149         for (u = UINT_MAX - 1024; u != 0; u++) {
150                 snprintf(buf, sizeof(buf), "%u", u);
151                 test_lookup_fail(fd, buf);
152         }
153 }
154 
155 int main(void)
156 {
157         unsigned int pid;
158         int fd;
159 
160         /*
161          * In theory this will loop indefinitely if kernel threads are exiled
162          * from /proc.
163          *
164          * Start with kthreadd.
165          */
166         pid = 2;
167         while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) {
168                 pid++;
169         }
170         /* EACCES if run as non-root. */
171         if (pid >= 1024)
172                 return 1;
173 
174         test_readdir(fd);
175         test_lookup(fd);
176 
177         return 0;
178 }
179 

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