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