From 8283452dfdc2d33b717b81f9a011dc95aa9017e3 Mon Sep 17 00:00:00 2001 Message-Id: <8283452dfdc2d33b717b81f9a011dc95aa9017e3@dist-git> From: Michal Privoznik Date: Tue, 6 Sep 2022 13:43:22 +0200 Subject: [PATCH] qemu_namespace: Fix a corner case in qemuDomainGetPreservedMounts() When setting up namespace for QEMU we look at mount points under /dev (like /dev/pts, /dev/mqueue/, etc.) because we want to preserve those (which is done by moving them to a temp location, unshare(), and then moving them back). We have a convenience helper - qemuDomainGetPreservedMounts() - that processes the mount table and (optionally) moves the other filesystems too. This helper is also used when attempting to create a path in NS, because the path, while starting with "/dev/" prefix, may actually lead to one of those filesystems that we preserved. And here comes the corner case: while we require the parent mount table to be in shared mode (equivalent of `mount --make-rshared /'), these mount events propagate iff the target path exist inside the slave mount table (= QEMU's private namespace). And since we create only a subset of /dev nodes, well, that assumption is not always the case. For instance, assume that a domain is already running, no hugepages were configured for it nor any hugetlbfs is mounted. Now, when a hugetlbfs is mounted into '/dev/hugepages', this is propagated into the QEMU's namespace, but since the target dir does not exist in the private /dev, the FS is not mounted in the namespace. Fortunately, this difference between namespaces is visible when comparing /proc/mounts and /proc/$PID/mounts (where PID is the QEMU's PID). Therefore, if possible we should look at the latter. Signed-off-by: Michal Privoznik Reviewed-by: Martin Kletzander (cherry picked from commit 46b03819ae8d833b11c2aaccb2c2a0361727f51b) Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2132176 Signed-off-by: Michal Privoznik --- src/qemu/qemu_namespace.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/src/qemu/qemu_namespace.c b/src/qemu/qemu_namespace.c index 4bff325a2c..fc286ab0be 100644 --- a/src/qemu/qemu_namespace.c +++ b/src/qemu/qemu_namespace.c @@ -110,6 +110,8 @@ qemuDomainGetPreservedMountPath(virQEMUDriverConfig *cfg, * b) generate backup path for all the entries in a) * * Any of the return pointers can be NULL. Both arrays are NULL-terminated. + * Get the mount table either from @vm's PID (if running), or from the + * namespace we're in (if @vm's not running). * * Returns 0 on success, -1 otherwise (with error reported) */ @@ -124,12 +126,18 @@ qemuDomainGetPreservedMounts(virQEMUDriverConfig *cfg, size_t nmounts = 0; g_auto(GStrv) paths = NULL; g_auto(GStrv) savePaths = NULL; + g_autofree char *mountsPath = NULL; size_t i; if (ndevPath) *ndevPath = 0; - if (virFileGetMountSubtree(QEMU_PROC_MOUNTS, "/dev", &mounts, &nmounts) < 0) + if (vm->pid > 0) + mountsPath = g_strdup_printf("/proc/%lld/mounts", (long long) vm->pid); + else + mountsPath = g_strdup(QEMU_PROC_MOUNTS); + + if (virFileGetMountSubtree(mountsPath, "/dev", &mounts, &nmounts) < 0) return -1; if (nmounts == 0) -- 2.38.1