linux-kernel - Re: [PATCH v3] proc: proc_pid_ns takes super

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Date:   Tue, 19 May 2020 00:36:34 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Alexey Gladkov <gladkov.alexey@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        syzbot <syzbot+c1af344512918c61362c@...kaller.appspotmail.com>,
        jmorris@...ei.org, linux-next@...r.kernel.org,
        linux-security-module@...r.kernel.org, serge@...lyn.com,
        sfr@...b.auug.org.au, syzkaller-bugs@...glegroups.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v3] proc: proc_pid_ns takes super_block as an argument

I would shorten like below:

syzbot found that

  touch /proc/testfile

causes NULL pointer dereference at tomoyo_get_local_path()
because inode of the dentry is NULL.

Before c59f415a7cb6, Tomoyo received pid_ns from proc's s_fs_info
directly. Since proc_pid_ns() can only work with inode, using it in
the tomoyo_get_local_path() was wrong.

To avoid creating more functions for getting proc_ns, change the
argument type of the proc_pid_ns() function. Then, Tomoyo can use
the existing super_block to get pid_ns.