linux-kernel - Re: Have RESOLVE_* flags superseded AT

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Message-ID: <927228.1583162604@warthog.procyon.org.uk>
Date:   Mon, 02 Mar 2020 15:23:24 +0000
From:   David Howells <dhowells@...hat.com>
To:     Aleksa Sarai <cyphar@...har.com>
Cc:     dhowells@...hat.com,
        Christian Brauner <christian.brauner@...ntu.com>,
        Florian Weimer <fweimer@...hat.com>, linux-api@...r.kernel.org,
        viro@...iv.linux.org.uk, metze@...ba.org,
        torvalds@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Have RESOLVE_* flags superseded AT_* flags for new syscalls?

Aleksa Sarai <cyphar@...har.com> wrote:

> My counter-argument is that most people actually want
> RESOLVE_NO_SYMLINKS (as evidenced by the countless symlink-related
> security bugs -- many of which used O_NOFOLLOW incorrectly), it just
> wasn't available before Linux 5.6.

I would quibble as to whether they actually want this in all situations.
There are some in which the difference in behaviour will conceivably break
things - though that's more the case for things like stat(), statx(), fsinfo()
and getxattr() where you might want to be able to query a specific symlink
than for openat2() where you almost always want to follow it (save O_PATH |
O_NOFOLLOW).

However, if you're okay with me adding, say, RESOLVE_NO_TERMINAL_SYMLINK and
RESOLVE_NO_TERMINAL_AUTOMOUNT, I can use these flags.

I don't want to have to allow both RESOLVE_* and AT_*.

David