procfs: do not list TID 0 in /proc/<pid>/task

If a task exits concurrently, task_pid_nr_ns may return 0.

[akpm@linux-foundation.org: coding style tweaks]
[adobriyan@gmail.com: test that /proc/*/task doesn't contain "0"]
Link: https://lkml.kernel.org/r/YV88AnVzHxPafQ9o@localhost.localdomain
Link: https://lkml.kernel.org/r/8735pn5dx7.fsf@oldenburg.str.redhat.com
Signed-off-by: Florian Weimer <fweimer@redhat.com>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 533d583..5541de9 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3799,7 +3799,10 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
             task = next_tid(task), ctx->pos++) {
                char name[10 + 1];
                unsigned int len;
+
                tid = task_pid_nr_ns(task, ns);
+               if (!tid)
+                       continue;       /* The task has just exited. */
                len = snprintf(name, sizeof(name), "%u", tid);
                if (!proc_fill_cache(file, ctx, name, len,
                                proc_task_instantiate, task, NULL)) {

diff --git a/tools/testing/selftests/proc/.gitignore b/tools/testing/selftests/proc/.gitignore
index 8f3e72e..c4e6a34 100644 (file)
--- a/tools/testing/selftests/proc/.gitignore
+++ b/tools/testing/selftests/proc/.gitignore
@@ -11,6 +11,7 @@
 /proc-self-syscall
 /proc-self-wchan
 /proc-subset-pid
+/proc-tid0
 /proc-uptime-001
 /proc-uptime-002
 /read

diff --git a/tools/testing/selftests/proc/Makefile b/tools/testing/selftests/proc/Makefile
index 1054e40..219fc61 100644 (file)
--- a/tools/testing/selftests/proc/Makefile
+++ b/tools/testing/selftests/proc/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 CFLAGS += -Wall -O2 -Wno-unused-function
 CFLAGS += -D_GNU_SOURCE
+LDFLAGS += -pthread
 
 TEST_GEN_PROGS :=
 TEST_GEN_PROGS += fd-001-lookup
@@ -13,6 +14,7 @@ TEST_GEN_PROGS += proc-self-map-files-002
 TEST_GEN_PROGS += proc-self-syscall
 TEST_GEN_PROGS += proc-self-wchan
 TEST_GEN_PROGS += proc-subset-pid
+TEST_GEN_PROGS += proc-tid0
 TEST_GEN_PROGS += proc-uptime-001
 TEST_GEN_PROGS += proc-uptime-002
 TEST_GEN_PROGS += read

diff --git a/tools/testing/selftests/proc/proc-tid0.c b/tools/testing/selftests/proc/proc-tid0.c
new file mode 100644 (file)
index 0000000..58c1d7c
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-tid0.c
@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2021 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/*/task never contains "0".
+#include <sys/types.h>
+#include <dirent.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <pthread.h>
+
+static pid_t pid = -1;
+
+static void atexit_hook(void)
+{
+       if (pid > 0) {
+               kill(pid, SIGKILL);
+       }
+}
+
+static void *f(void *_)
+{
+       return NULL;
+}
+
+static void sigalrm(int _)
+{
+       exit(0);
+}
+
+int main(void)
+{
+       pid = fork();
+       if (pid == 0) {
+               /* child */
+               while (1) {
+                       pthread_t pth;
+                       pthread_create(&pth, NULL, f, NULL);
+                       pthread_join(pth, NULL);
+               }
+       } else if (pid > 0) {
+               /* parent */
+               atexit(atexit_hook);
+
+               char buf[64];
+               snprintf(buf, sizeof(buf), "/proc/%u/task", pid);
+
+               signal(SIGALRM, sigalrm);
+               alarm(1);
+
+               while (1) {
+                       DIR *d = opendir(buf);
+                       struct dirent *de;
+                       while ((de = readdir(d))) {
+                               if (strcmp(de->d_name, "0") == 0) {
+                                       exit(1);
+                               }
+                       }
+                       closedir(d);
+               }
+
+               return 0;
+       } else {
+               perror("fork");
+               return 1;
+       }
+}