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From:   Florian Weimer <fweimer@redhat.com>
To:     linux-fsdevel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Kees Cook <keescook@chromium.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH] procfs: Do not list TID 0 in /proc/<pid>/task
Date:   Wed, 29 Sep 2021 22:23:32 +0200
Message-ID: <8735pn5dx7.fsf@oldenburg.str.redhat.com>
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If a task exits concurrently, task_pid_nr_ns may return 0.

Signed-off-by: Florian Weimer <fweimer@redhat.com>
---
 fs/proc/base.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 533d5836eb9a..54f29399088f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3800,6 +3800,9 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
 		char name[10 + 1];
 		unsigned int len;
 		tid = task_pid_nr_ns(task, ns);
+		if (!tid)
+			/* The task has just exited. */
+			continue;
 		len = snprintf(name, sizeof(name), "%u", tid);
 		if (!proc_fill_cache(file, ctx, name, len,
 				proc_task_instantiate, task, NULL)) {
-- 
2.31.1