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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Jens Axboe <axboe@kernel.dk>
Subject: [PATCH 5.10 625/663] proc: dont allow async path resolution of /proc/thread-self components
Date:   Mon,  1 Mar 2021 17:14:33 +0100
Message-Id: <20210301161212.773203810@linuxfoundation.org>
In-Reply-To: <20210301161141.760350206@linuxfoundation.org>
References: <20210301161141.760350206@linuxfoundation.org>
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From: Jens Axboe <axboe@kernel.dk>

commit 0d4370cfe36b7f1719123b621a4ec4d9c7a25f89 upstream.

If this is attempted by an io-wq kthread, then return -EOPNOTSUPP as we
don't currently support that. Once we can get task_pid_ptr() doing the
right thing, then this can go away again.

Use PF_IO_WORKER for this to speciically target the io_uring workers.
Modify the /proc/self/ check to use PF_IO_WORKER as well.

Cc: stable@vger.kernel.org
Fixes: 8d4c3e76e3be ("proc: don't allow async path resolution of /proc/self components")
Reported-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/proc/self.c        |    2 +-
 fs/proc/thread_self.c |    7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

--- a/fs/proc/self.c
+++ b/fs/proc/self.c
@@ -20,7 +20,7 @@ static const char *proc_self_get_link(st
 	 * Not currently supported. Once we can inherit all of struct pid,
 	 * we can allow this.
 	 */
-	if (current->flags & PF_KTHREAD)
+	if (current->flags & PF_IO_WORKER)
 		return ERR_PTR(-EOPNOTSUPP);
 
 	if (!tgid)
--- a/fs/proc/thread_self.c
+++ b/fs/proc/thread_self.c
@@ -17,6 +17,13 @@ static const char *proc_thread_self_get_
 	pid_t pid = task_pid_nr_ns(current, ns);
 	char *name;
 
+	/*
+	 * Not currently supported. Once we can inherit all of struct pid,
+	 * we can allow this.
+	 */
+	if (current->flags & PF_IO_WORKER)
+		return ERR_PTR(-EOPNOTSUPP);
+
 	if (!pid)
 		return ERR_PTR(-ENOENT);
 	name = kmalloc(10 + 6 + 10 + 1, dentry ? GFP_KERNEL : GFP_ATOMIC);