From: Alyssa Ross <hi@alyssa.is>
To: linux-fsdevel@vger.kernel.org
Cc: Demi Marie Obenour <demiobenour@gmail.com>,
Aleksa Sarai <cyphar@cyphar.com>, Jann Horn <jannh@google.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
jlayton@kernel.org, Bruce Fields <bfields@fieldses.org>,
Al Viro <viro@zeniv.linux.org.uk>, Arnd Bergmann <arnd@arndb.de>,
shuah@kernel.org, David Howells <dhowells@redhat.com>,
Andy Lutomirski <luto@kernel.org>,
Christian Brauner <brauner@kernel.org>,
Tycho Andersen <tycho@tycho.pizza>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org
Subject: Safety of resolving untrusted paths with detached mount dirfd
Date: Wed, 19 Nov 2025 14:46:35 +0100 [thread overview]
Message-ID: <87cy5eqgn8.fsf@alyssa.is> (raw)
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Hello,
As we know, it's not safe to use chroot() for resolving untrusted paths
within some root, as a subdirectory could be moved outside of the
process root while walking the path[1]. On the other hand,
LOOKUP_BENEATH is supposed to be robust against this, and going by [2],
it sounds like resolving with the mount namespace root as dirfd should
also be.
My question is: would resolving an untrusted path against a detached
mount root dirfd opened with OPEN_TREE_CLONE (not necessarily a
filesystem root) also be expected to be robust against traversal issues?
i.e. can I rely on an untrusted path never resolving to a path that
isn't under the mount root?
[1]: https://lore.kernel.org/lkml/CAG48ez30WJhbsro2HOc_DR7V91M+hNFzBP5ogRMZaxbAORvqzg@mail.gmail.com/
[2]: https://lore.kernel.org/lkml/C89D720F-3CC4-4FA9-9CBB-E41A67360A6B@amacapital.net/
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next reply other threads:[~2025-11-19 14:25 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-19 13:46 Alyssa Ross [this message]
2025-11-19 18:34 ` Safety of resolving untrusted paths with detached mount dirfd David Laight
2025-11-20 2:18 ` Aleksa Sarai
2025-11-20 2:39 ` Demi Marie Obenour
2025-11-20 9:24 ` Aleksa Sarai
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