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