Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 13 Nov 2019 02:03:07 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Aleksa Sarai <cyphar@cyphar.com>
Cc:     Jeff Layton <jlayton@kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Arnd Bergmann <arnd@arndb.de>,
        David Howells <dhowells@redhat.com>,
        Shuah Khan <shuah@kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Andy Lutomirski <luto@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Tycho Andersen <tycho@tycho.ws>,
        David Drysdale <drysdale@google.com>,
        Chanho Min <chanho.min@lge.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Christian Brauner <christian@brauner.io>,
        Aleksa Sarai <asarai@suse.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org,
        linux-api@vger.kernel.org, libc-alpha@sourceware.org,
        linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org,
        linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
        linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org
Subject: Re: [PATCH v15 5/9] namei: LOOKUP_IN_ROOT: chroot-like scoped
 resolution
Message-ID: <20191113020307.GB26530@ZenIV.linux.org.uk>
References: <20191105090553.6350-1-cyphar@cyphar.com>
 <20191105090553.6350-6-cyphar@cyphar.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20191105090553.6350-6-cyphar@cyphar.com>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Nov 05, 2019 at 08:05:49PM +1100, Aleksa Sarai wrote:

> @@ -2277,12 +2277,20 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
>  
>  	nd->m_seq = read_seqbegin(&mount_lock);
>  
> -	/* Figure out the starting path and root (if needed). */
> -	if (*s == '/') {
> +	/* Absolute pathname -- fetch the root. */
> +	if (flags & LOOKUP_IN_ROOT) {
> +		/* With LOOKUP_IN_ROOT, act as a relative path. */
> +		while (*s == '/')
> +			s++;

Er...  Why bother skipping slashes?  I mean, not only link_path_walk()
will skip them just fine, you are actually risking breakage in this:
                if (*s && unlikely(!d_can_lookup(dentry))) {
                        fdput(f);
                        return ERR_PTR(-ENOTDIR);
                }
which is downstream from there with you patch, AFAICS.