From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Alexey Dobriyan <adobriyan@gmail.com>,
James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
LSM List <linux-security-module@vger.kernel.org>,
Paul Moore <paul@paul-moore.com>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
Eric Paris <eparis@parisplace.org>,
SElinux list <selinux@vger.kernel.org>,
Casey Schaufler <casey@schaufler-ca.com>,
Eric Biederman <ebiederm@xmission.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Stephen Brennan <stephen.s.brennan@oracle.com>
Subject: Re: [PATCH v4] proc: Allow pid_revalidate() during LOOKUP_RCU
Date: Tue, 5 Jan 2021 12:38:31 -0800 [thread overview]
Message-ID: <CAHk-=wiP9EAP=JHGKG5LUCusVjVzTQoPVyweJkrX5dP=T_NxXw@mail.gmail.com> (raw)
In-Reply-To: <20210105195937.GX3579531@ZenIV.linux.org.uk>
On Tue, Jan 5, 2021 at 12:00 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> We are not guaranteed the locking environment that would prevent
> dentry getting renamed right under us. And it's possible for
> old long name to be freed after rename, leading to UAF here.
This whole thing isn't important enough to get the dentry lock. It's
more of a hint than anything else.
Why isn't the fix to just use READ_ONCE() of the name pointer, and do
it under RCU?
That's what dentry_name() does for the much more complex case of
actually even following parent data for a depth up to 4, much less
just a single name.
So instead of
spin_lock(&dentry->d_lock);
audit_log_untrustedstring(ab, dentry->d_name.name);
spin_unlock(&dentry->d_lock);
why not
rcu_read_lock();
audit_log_untrustedstring(ab,
READ_ONCE(dentry->d_name.name));
rcu_read_unlock();
which looks a lot more in line with the other dentry path functions.
Maybe even have this as part of fs/d_path.c and try to get rid of
magic internal dentry name knowledge from the audit code?
Linus
next prev parent reply other threads:[~2021-01-05 20:39 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-04 23:21 [PATCH v4] proc: Allow pid_revalidate() during LOOKUP_RCU Stephen Brennan
2021-01-05 5:59 ` Al Viro
2021-01-05 16:50 ` Al Viro
2021-01-05 17:45 ` Al Viro
2021-01-05 19:59 ` Al Viro
2021-01-05 20:38 ` Linus Torvalds [this message]
2021-01-05 21:12 ` Al Viro
2021-01-05 23:25 ` Stephen Brennan
2021-01-06 0:00 ` Paul Moore
2021-01-06 0:38 ` Al Viro
2021-01-06 2:43 ` Paul Moore
2021-01-14 22:51 ` Stephen Brennan
2021-01-06 0:56 ` Stephen Brennan
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