From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C1B2F49B21F; Wed, 2 Sep 2026 13:03:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788354235; cv=none; b=M2O2aKp403731LOxYza8kk3jiZmz/1IvbRXA9i119twOM82t6xmSkhF/5Jypsi91MuVnuTPEuNtwFzUFfW2GVfVh7e5FBmHp8WDp8TybAz+JrEIUSt+sLgACPRvv49I2yPc4zZt23RdhwyMyG9sGC4l6QcDcHWvqMBmgVQKP2RI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788354235; c=relaxed/simple; bh=KywRZ7u7+wKpsLZU80tvxRa+CLPFR3Qh1sZrmVT+4Jk=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=FrajTBvtqqJzTNazChPA+c1rynzG7E7ZJzO7r9lCo7nT/AdDTOR6wq4XdSduv8dFp4hFfzPfeR2E2j1Wv2aFdBH52m9IVNq1aaJDEwcnZJQcBm4Tr8ozrH3JMbMTCac+RZec3svNWuQDZnWLh+4GMWF8nEdQEyYk9j9+txvXxkU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=VAizg2gQ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="VAizg2gQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 814311F00A3A; Wed, 2 Sep 2026 13:03:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788354233; bh=MTGGl3RwcuCFV/bUtDz32VMfXUuvDipc4YWXpSVJ+U4=; h=Subject:From:To:Cc:Date:In-Reply-To:References; b=VAizg2gQ6bti2K/G5cmEO/yrnvCZnBCqK75puimyI5sciyVcwGmhGAV+sXItvo6wB akEeMM1nJxts2Z20NVdA8Mh4jFz19abshLk+e1sDxl5MsxdyuUxVSN+3peCN5Kv3Uv 218RfiUgmpHR8kUg2qqrdZ7TBx2oHxwzDM3xB0TeIj8FQGiTvxO6MMcMyLdwGMFj1W iIw4T/zPnp1G8ln3EeoOhjdphhUUOHpxczReRMe7nM+kfgVDqt5xXw+BbaRtoBGX2d sxYrcUHquzgZTFkM1xln4InV01fTUxjsdeo5wVYc/GkvLORSiATUZgreHwx1iqBKRW jHE37ioqgc/3w== Message-ID: Subject: Re: [PATCH v2] fs/locks: filter OFD locks from /proc/locks for foreign pid namespaces From: Jeff Layton To: Tao Cui , linux-fsdevel@vger.kernel.org, cel@kernel.org Cc: alex.aring@gmail.com, viro@zeniv.linux.org.uk, brauner@kernel.org, linux-kernel@vger.kernel.org, avagin@openvz.org, khorenko@virtuozzo.com, bcodding@redhat.com, Tao Cui Date: Wed, 02 Sep 2026 09:03:50 -0400 In-Reply-To: <20260902125139.975253-1-cui.tao@linux.dev> References: <20260902125139.975253-1-cui.tao@linux.dev> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Wed, 2026-09-02 at 20:51 +0800, Tao Cui wrote: > From: Tao Cui >=20 > Since Linux 4.9, /proc/locks only shows locks whose owning process is > visible in the reader's pid namespace. The check cannot see the > owner of an OFD lock, though: locks_translate_pid() always returns > -1 for FL_OFDLCK, so an OFD lock held outside of that namespace > bypasses the filter and is shown with its device/inode numbers and > byte range, e.g. >=20 > 4: OFDLCK ADVISORY WRITE -1 fd:00:70536961 0 EOF >=20 > This was observed on a Kubernetes node: a pod reading /proc/locks > listed the OFD write lock of an unrelated host process, while the > POSIX locks of the very same process were correctly hidden. The > device/inode pair identifies which host file is locked, the byte > range discloses where it is actively written, and the > appearance/disappearance of entries reflects host task activity, > contrary to the documented per-pidns visibility of /proc/locks > (proc_locks(5)). >=20 > OFD locks record the owner tgid in flc_pid, so use it for the > visibility decision in locks_show(), mirroring what > locks_translate_pid() does for POSIX locks. The pid column is still > reported as -1 for OFD locks; only the filter decision changes. > Remote locks keep their negative flc_pid and stay visible as before. >=20 > Verified with an OFD and a POSIX write lock held in the initial pid > namespace while a process in a fresh pid namespace reads /proc/locks: > the OFD entry is visible without this patch and hidden with it, the > POSIX entry is hidden in both cases. >=20 > Signed-off-by: Tao Cui >=20 > --- >=20 > Changes since v1: keep remote OFD locks (negative flc_pid) visible in > non-initial pid namespaces, as locks_translate_pid() does for remote > POSIX locks. > --- > fs/locks.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) >=20 > diff --git a/fs/locks.c b/fs/locks.c > index 6e4ff7fcec05..4af1385682e4 100644 > --- a/fs/locks.c > +++ b/fs/locks.c > @@ -3022,6 +3022,25 @@ static int locks_show(struct seq_file *f, void *v) > =20 > cur =3D hlist_entry(v, struct file_lock_core, flc_link); > =20 > + /* > + * OFD locks are reported with pid -1, so the filter below cannot see > + * their owner; flc_pid holds the owner tgid, so filter on it. > + * Remote locks keep a negative flc_pid and stay visible as before. > + */ > + if ((cur->flc_flags & FL_OFDLCK) && cur->flc_pid > 0 && > + proc_pidns !=3D &init_pid_ns) { > + struct pid *pid; > + bool visible =3D false; > + > + rcu_read_lock(); > + pid =3D find_pid_ns(cur->flc_pid, &init_pid_ns); > + if (pid) > + visible =3D pid_nr_ns(pid, proc_pidns) !=3D 0; > + rcu_read_unlock(); > + if (!visible) > + return 0; > + } > + > if (locks_translate_pid(cur, proc_pidns) =3D=3D 0) > return 0; > =20 First: I think this may be the wrong place to do this. Why not fold this change into locks_translate_pid()? It seems like we'd have inconsistent results wrt lock visibility between /proc/locks and F_GETLK if you do this here. Thinking about this some more though, I wonder if trying to hide these locks is the right thing to do. These locks do exist and they do block you from acquiring a lock. If you go to look at /proc/locks and don't see them, that seems confusing. Would we be better off showing all the locks and reporting the pid as a negative value for ones acquired in foreign namespaces, like we do for remote locks? --=20 Jeff Layton