1 files changed, 178 insertions, 0 deletions
diff --git a/tools/testing/selftests/proc/fd-003-kthread.c b/tools/testing/selftests/proc/fd-003-kthread.c
new file mode 100644
index 0000000000..dc591f97b6
--- /dev/null
+++ b/tools/testing/selftests/proc/fd-003-kthread.c
@@ -0,0 +1,178 @@
+/*
+ * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
+ *
+ * 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/$KERNEL_THREAD/fd/ is empty.
+
+#undef NDEBUG
+#include <sys/syscall.h>
+#include <assert.h>
+#include <dirent.h>
+#include <limits.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "proc.h"
+
+#define PF_KHTREAD 0x00200000
+
+/*
+ * Test for kernel threadness atomically with openat().
+ *
+ * Return /proc/$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;
+}