From: Alexey Dobriyan <adobriyan@xxxxxxxxx> Subject: tools/testing/selftests/proc: test /proc/*/fd a bit (+ PF_KTHREAD is ABI!) * Test lookup in /proc/self/fd. "map_files" lookup story showed that lookup is not that simple. * Test that all those symlinks open the same file. Check with (st_dev, st_info). * Test that kernel threads do not have anything in their /proc/*/fd/ directory. Now this is where things get interesting. First, kernel threads aren't pinned by /proc/self or equivalent, thus some "atomicity" is required. Second, ->comm can contain whitespace and ')'. No, they are not escaped. Third, the only reliable way to check if process is kernel thread appears to be field #9 in /proc/*/stat. This field is struct task_struct::flags in decimal! Check is done by testing PF_KTHREAD flags like we do in kernel. PF_KTREAD value is a part of userspace ABI !!! Other methods for determining kernel threadness are not reliable: * RSS can be 0 if everything is swapped, even while reading from /proc/self. * ->total_vm CAN BE ZERO if process is finishing munmap(NULL, whole address space); * /proc/*/maps and similar files can be empty because unmapping everything works. Read returning 0 can't distinguish between kernel thread and such suicide process. Link: http://lkml.kernel.org/r/20180505000414.GA15090@avx2 Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- tools/testing/selftests/proc/.gitignore | 3 tools/testing/selftests/proc/Makefile | 5 tools/testing/selftests/proc/fd-001-lookup.c | 168 ++++++++++++++ tools/testing/selftests/proc/fd-002-posix-eq.c | 57 ++++ tools/testing/selftests/proc/fd-003-kthread.c | 178 +++++++++++++++ tools/testing/selftests/proc/proc-uptime.h | 16 - tools/testing/selftests/proc/proc.h | 39 +++ tools/testing/selftests/proc/read.c | 17 - 8 files changed, 451 insertions(+), 32 deletions(-) diff -puN /dev/null tools/testing/selftests/proc/fd-001-lookup.c --- /dev/null +++ a/tools/testing/selftests/proc/fd-001-lookup.c @@ -0,0 +1,168 @@ +/* + * Copyright © 2018 Alexey Dobriyan <adobriyan@xxxxxxxxx> + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ +// Test /proc/*/fd lookup. +#define _GNU_SOURCE +#undef NDEBUG +#include <assert.h> +#include <dirent.h> +#include <errno.h> +#include <limits.h> +#include <sched.h> +#include <stdio.h> +#include <unistd.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> + +#include "proc.h" + +/* lstat(2) has more "coverage" in case non-symlink pops up somehow. */ +static void test_lookup_pass(const char *pathname) +{ + struct stat st; + ssize_t rv; + + memset(&st, 0, sizeof(struct stat)); + rv = lstat(pathname, &st); + assert(rv == 0); + assert(S_ISLNK(st.st_mode)); +} + +static void test_lookup_fail(const char *pathname) +{ + struct stat st; + ssize_t rv; + + rv = lstat(pathname, &st); + assert(rv == -1 && errno == ENOENT); +} + +static void test_lookup(unsigned int fd) +{ + char buf[64]; + unsigned int c; + unsigned int u; + int i; + + snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd); + test_lookup_pass(buf); + + /* leading junk */ + for (c = 1; c <= 255; c++) { + if (c == '/') + continue; + snprintf(buf, sizeof(buf), "/proc/self/fd/%c%u", c, fd); + test_lookup_fail(buf); + } + + /* trailing junk */ + for (c = 1; c <= 255; c++) { + if (c == '/') + continue; + snprintf(buf, sizeof(buf), "/proc/self/fd/%u%c", fd, c); + test_lookup_fail(buf); + } + + for (i = INT_MIN; i < INT_MIN + 1024; i++) { + snprintf(buf, sizeof(buf), "/proc/self/fd/%d", i); + test_lookup_fail(buf); + } + for (i = -1024; i < 0; i++) { + snprintf(buf, sizeof(buf), "/proc/self/fd/%d", i); + test_lookup_fail(buf); + } + for (u = INT_MAX - 1024; u <= (unsigned int)INT_MAX + 1024; u++) { + snprintf(buf, sizeof(buf), "/proc/self/fd/%u", u); + test_lookup_fail(buf); + } + for (u = UINT_MAX - 1024; u != 0; u++) { + snprintf(buf, sizeof(buf), "/proc/self/fd/%u", u); + test_lookup_fail(buf); + } + + +} + +int main(void) +{ + struct dirent *de; + unsigned int fd, target_fd; + + if (unshare(CLONE_FILES) == -1) + return 1; + + /* Wipe fdtable. */ + do { + DIR *d; + + d = opendir("/proc/self/fd"); + if (!d) + return 1; + + de = xreaddir(d); + assert(de->d_type == DT_DIR); + assert(streq(de->d_name, ".")); + + de = xreaddir(d); + assert(de->d_type == DT_DIR); + assert(streq(de->d_name, "..")); +next: + de = xreaddir(d); + if (de) { + unsigned long long fd_ull; + unsigned int fd; + char *end; + + assert(de->d_type == DT_LNK); + + fd_ull = xstrtoull(de->d_name, &end); + assert(*end == '\0'); + assert(fd_ull == (unsigned int)fd_ull); + + fd = fd_ull; + if (fd == dirfd(d)) + goto next; + close(fd); + } + + closedir(d); + } while (de); + + /* Now fdtable is clean. */ + + fd = open("/", O_PATH|O_DIRECTORY); + assert(fd == 0); + test_lookup(fd); + close(fd); + + /* Clean again! */ + + fd = open("/", O_PATH|O_DIRECTORY); + assert(fd == 0); + /* Default RLIMIT_NOFILE-1 */ + target_fd = 1023; + while (target_fd > 0) { + if (dup2(fd, target_fd) == target_fd) + break; + target_fd /= 2; + } + assert(target_fd > 0); + close(fd); + test_lookup(target_fd); + close(target_fd); + + return 0; +} diff -puN /dev/null tools/testing/selftests/proc/fd-002-posix-eq.c --- /dev/null +++ a/tools/testing/selftests/proc/fd-002-posix-eq.c @@ -0,0 +1,57 @@ +/* + * Copyright © 2018 Alexey Dobriyan <adobriyan@xxxxxxxxx> + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ +// Test that open(/proc/*/fd/*) opens the same file. +#undef NDEBUG +#include <assert.h> +#include <stdio.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> +#include <unistd.h> + +int main(void) +{ + int fd0, fd1, fd2; + struct stat st0, st1, st2; + char buf[64]; + int rv; + + fd0 = open("/", O_DIRECTORY|O_RDONLY); + assert(fd0 >= 0); + + snprintf(buf, sizeof(buf), "/proc/self/fd/%u", fd0); + fd1 = open(buf, O_RDONLY); + assert(fd1 >= 0); + + snprintf(buf, sizeof(buf), "/proc/thread-self/fd/%u", fd0); + fd2 = open(buf, O_RDONLY); + assert(fd2 >= 0); + + rv = fstat(fd0, &st0); + assert(rv == 0); + rv = fstat(fd1, &st1); + assert(rv == 0); + rv = fstat(fd2, &st2); + assert(rv == 0); + + assert(st0.st_dev == st1.st_dev); + assert(st0.st_ino == st1.st_ino); + + assert(st0.st_dev == st2.st_dev); + assert(st0.st_ino == st2.st_ino); + + return 0; +} diff -puN /dev/null tools/testing/selftests/proc/fd-003-kthread.c --- /dev/null +++ a/tools/testing/selftests/proc/fd-003-kthread.c @@ -0,0 +1,178 @@ +/* + * Copyright © 2018 Alexey Dobriyan <adobriyan@xxxxxxxxx> + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ +// Test that /proc/$KERNEL_THREAD/fd/ is empty. +#define _GNU_SOURCE +#undef NDEBUG +#include <sys/syscall.h> +#include <assert.h> +#include <dirent.h> +#include <limits.h> +#include <stdio.h> +#include <string.h> +#include <sys/types.h> +#include <sys/stat.h> +#include <fcntl.h> +#include <unistd.h> + +#include "proc.h" + +#define PF_KHTREAD 0x00200000 + +/* + * Test for kernel threadness atomically with openat(). + * + * Return /proc/$PID/fd descriptor if process is kernel thread. + * Return -1 if a process is userspace process. + */ +static int kernel_thread_fd(unsigned int pid) +{ + unsigned int flags = 0; + char buf[4096]; + int dir_fd, fd; + ssize_t rv; + + snprintf(buf, sizeof(buf), "/proc/%u", pid); + dir_fd = open(buf, O_RDONLY|O_DIRECTORY); + if (dir_fd == -1) + return -1; + + /* + * Believe it or not, struct task_struct::flags is directly exposed + * to userspace! + */ + fd = openat(dir_fd, "stat", O_RDONLY); + if (fd == -1) { + close(dir_fd); + return -1; + } + rv = read(fd, buf, sizeof(buf)); + close(fd); + if (0 < rv && rv <= sizeof(buf)) { + unsigned long long flags_ull; + char *p, *end; + int i; + + assert(buf[rv - 1] == '\n'); + buf[rv - 1] = '\0'; + + /* Search backwards: ->comm can contain whitespace and ')'. */ + for (i = 0; i < 43; i++) { + p = strrchr(buf, ' '); + assert(p); + *p = '\0'; + } + + p = strrchr(buf, ' '); + assert(p); + + flags_ull = xstrtoull(p + 1, &end); + assert(*end == '\0'); + assert(flags_ull == (unsigned int)flags_ull); + + flags = flags_ull; + } + + fd = -1; + if (flags & PF_KHTREAD) { + fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY); + } + close(dir_fd); + return fd; +} + +static void test_readdir(int fd) +{ + DIR *d; + struct dirent *de; + + d = fdopendir(fd); + assert(d); + + de = xreaddir(d); + assert(streq(de->d_name, ".")); + assert(de->d_type == DT_DIR); + + de = xreaddir(d); + assert(streq(de->d_name, "..")); + assert(de->d_type == DT_DIR); + + de = xreaddir(d); + assert(!de); +} + +static inline int sys_statx(int dirfd, const char *pathname, int flags, + unsigned int mask, void *stx) +{ + return syscall(SYS_statx, dirfd, pathname, flags, mask, stx); +} + +static void test_lookup_fail(int fd, const char *pathname) +{ + char stx[256] __attribute__((aligned(8))); + int rv; + + rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx); + assert(rv == -1 && errno == ENOENT); +} + +static void test_lookup(int fd) +{ + char buf[64]; + unsigned int u; + int i; + + for (i = INT_MIN; i < INT_MIN + 1024; i++) { + snprintf(buf, sizeof(buf), "%d", i); + test_lookup_fail(fd, buf); + } + for (i = -1024; i < 1024; i++) { + snprintf(buf, sizeof(buf), "%d", i); + test_lookup_fail(fd, buf); + } + for (u = INT_MAX - 1024; u < (unsigned int)INT_MAX + 1024; u++) { + snprintf(buf, sizeof(buf), "%u", u); + test_lookup_fail(fd, buf); + } + for (u = UINT_MAX - 1024; u != 0; u++) { + snprintf(buf, sizeof(buf), "%u", u); + test_lookup_fail(fd, buf); + } +} + +int main(void) +{ + unsigned int pid; + int fd; + + /* + * In theory this will loop indefinitely if kernel threads are exiled + * from /proc. + * + * Start with kthreadd. + */ + pid = 2; + while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) { + pid++; + } + /* EACCES if run as non-root. */ + if (pid >= 1024) + return 1; + + test_readdir(fd); + test_lookup(fd); + + return 0; +} diff -puN tools/testing/selftests/proc/.gitignore~proc-test-proc-fd-a-bit-pf_kthread-is-abi tools/testing/selftests/proc/.gitignore --- a/tools/testing/selftests/proc/.gitignore~proc-test-proc-fd-a-bit-pf_kthread-is-abi +++ a/tools/testing/selftests/proc/.gitignore @@ -1,3 +1,6 @@ +/fd-001-lookup +/fd-002-posix-eq +/fd-003-kthread /proc-loadavg-001 /proc-self-map-files-001 /proc-self-map-files-002 diff -puN tools/testing/selftests/proc/Makefile~proc-test-proc-fd-a-bit-pf_kthread-is-abi tools/testing/selftests/proc/Makefile --- a/tools/testing/selftests/proc/Makefile~proc-test-proc-fd-a-bit-pf_kthread-is-abi +++ a/tools/testing/selftests/proc/Makefile @@ -1,6 +1,9 @@ -CFLAGS += -Wall -O2 +CFLAGS += -Wall -O2 -Wno-unused-function TEST_GEN_PROGS := +TEST_GEN_PROGS += fd-001-lookup +TEST_GEN_PROGS += fd-002-posix-eq +TEST_GEN_PROGS += fd-003-kthread TEST_GEN_PROGS += proc-loadavg-001 TEST_GEN_PROGS += proc-self-map-files-001 TEST_GEN_PROGS += proc-self-map-files-002 diff -puN /dev/null tools/testing/selftests/proc/proc.h --- /dev/null +++ a/tools/testing/selftests/proc/proc.h @@ -0,0 +1,39 @@ +#pragma once +#undef NDEBUG +#include <assert.h> +#include <dirent.h> +#include <errno.h> +#include <stdbool.h> +#include <stdlib.h> +#include <string.h> + +static inline bool streq(const char *s1, const char *s2) +{ + return strcmp(s1, s2) == 0; +} + +static unsigned long long xstrtoull(const char *p, char **end) +{ + if (*p == '0') { + *end = (char *)p + 1; + return 0; + } else if ('1' <= *p && *p <= '9') { + unsigned long long val; + + errno = 0; + val = strtoull(p, end, 10); + assert(errno == 0); + return val; + } else + assert(0); +} + +static struct dirent *xreaddir(DIR *d) +{ + struct dirent *de; + + errno = 0; + de = readdir(d); + assert(de || errno == 0); + return de; +} diff -puN tools/testing/selftests/proc/proc-uptime.h~proc-test-proc-fd-a-bit-pf_kthread-is-abi tools/testing/selftests/proc/proc-uptime.h --- a/tools/testing/selftests/proc/proc-uptime.h~proc-test-proc-fd-a-bit-pf_kthread-is-abi +++ a/tools/testing/selftests/proc/proc-uptime.h @@ -20,21 +20,7 @@ #include <stdlib.h> #include <unistd.h> -static unsigned long long xstrtoull(const char *p, char **end) -{ - if (*p == '0') { - *end = (char *)p + 1; - return 0; - } else if ('1' <= *p && *p <= '9') { - unsigned long long val; - - errno = 0; - val = strtoull(p, end, 10); - assert(errno == 0); - return val; - } else - assert(0); -} +#include "proc.h" static void proc_uptime(int fd, uint64_t *uptime, uint64_t *idle) { diff -puN tools/testing/selftests/proc/read.c~proc-test-proc-fd-a-bit-pf_kthread-is-abi tools/testing/selftests/proc/read.c --- a/tools/testing/selftests/proc/read.c~proc-test-proc-fd-a-bit-pf_kthread-is-abi +++ a/tools/testing/selftests/proc/read.c @@ -31,22 +31,7 @@ #include <fcntl.h> #include <unistd.h> -static inline bool streq(const char *s1, const char *s2) -{ - return strcmp(s1, s2) == 0; -} - -static struct dirent *xreaddir(DIR *d) -{ - struct dirent *de; - - errno = 0; - de = readdir(d); - if (!de && errno != 0) { - exit(1); - } - return de; -} +#include "proc.h" static void f_reg(DIR *d, const char *filename) { _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
