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From fd06fc3affcda0d7af1721c26915b8d87e0b2614 Mon Sep 17 00:00:00 2001
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Message-Id: <fd06fc3affcda0d7af1721c26915b8d87e0b2614@dist-git>
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From: Michal Privoznik <mprivozn@redhat.com>
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Date: Tue, 7 Feb 2023 15:06:32 +0100
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Subject: [PATCH] qemu_namespace: Deal with nested mounts when umount()-ing
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/dev
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In one of recent commits (v9.0.0-rc1~106) I've made our QEMU
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namespace code umount the original /dev. One of the reasons was
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enhanced security, because previously we just mounted a tmpfs
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over the original /dev. Thus a malicious QEMU could just
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umount("/dev") and it would get to the original /dev with all
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nodes.
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Now, on some systems this introduced a regression:
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failed to umount devfs on /dev: Device or resource busy
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But how this could be? We've moved all file systems mounted under
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/dev to a temporary location. Or have we? As it turns out, not
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quite. If there are two file systems mounted on the same target,
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e.g. like this:
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mount -t tmpfs tmpfs /dev/shm/ && mount -t tmpfs tmpfs /dev/shm/
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then only the top most (i.e. the last one) is moved. See
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qemuDomainUnshareNamespace() for more info.
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Now, we could enhance our code to deal with these "doubled" mount
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points. Or, since it is the top most file system that is
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accessible anyways (and this one is preserved), we can
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umount("/dev") in a recursive fashion.
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Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2167302
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Fixes: 379c0ce4bfed8733dfbde557c359eecc5474ce38
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Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
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Reviewed-by: Jim Fehlig <jfehlig@suse.com>
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(cherry picked from commit 5155ab4b2a704285505dfea6ffee8b980fdaa29e)
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Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
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---
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src/qemu/qemu_namespace.c | 2 +-
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1 file changed, 1 insertion(+), 1 deletion(-)
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diff --git a/src/qemu/qemu_namespace.c b/src/qemu/qemu_namespace.c
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index 5769a4dfe0..5fc043bd62 100644
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--- a/src/qemu/qemu_namespace.c
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+++ b/src/qemu/qemu_namespace.c
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@@ -777,7 +777,7 @@ qemuDomainUnshareNamespace(virQEMUDriverConfig *cfg,
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}
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#if defined(__linux__)
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- if (umount("/dev") < 0) {
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+ if (umount2("/dev", MNT_DETACH) < 0) {
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virReportSystemError(errno, "%s", _("failed to umount devfs on /dev"));
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return -1;
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}
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--
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2.39.1
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