[libvirt] [PATCH 5/5] qemuDomainDetachDeviceUnlink: Don't unlink files we haven't created

[Michal Privoznik]

Even though there are several checks before calling this function
and for some scenarios we don't call it at all (e.g. on disk hot
unplug), it may be possible to sneak in some weird files (e.g. if
domain would have RNG with /dev/shm/some_file as its backend). No
matter how improbable, we shouldn't unlink it as we would be
unlinking a file from the host which we haven't created in the
first place.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_domain.c | 86 ++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 76 insertions(+), 10 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 60f8f01..c393d5e 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -8395,14 +8395,32 @@ qemuDomainDetachDeviceUnlinkHelper(pid_t pid ATTRIBUTE_UNUSED,
 static int
 qemuDomainDetachDeviceUnlink(virQEMUDriverPtr driver ATTRIBUTE_UNUSED,
                              virDomainObjPtr vm,
-                             const char *file)
+                             const char *file,
+                             char * const *devMountsPath,
+                             size_t ndevMountsPath)
 {
-    if (virProcessRunInMountNamespace(vm->pid,
-                                      qemuDomainDetachDeviceUnlinkHelper,
-                                      (void *)file) < 0)
-        return -1;
+    int ret = -1;
+    size_t i;
 
-    return 0;
+    if (STRPREFIX(file, DEVPREFIX)) {
+        for (i = 0; i < ndevMountsPath; i++) {
+            if (STREQ(devMountsPath[i], "/dev"))
+                continue;
+            if (STRPREFIX(file, devMountsPath[i]))
+                break;
+        }
+
+        if (i == ndevMountsPath) {
+            if (virProcessRunInMountNamespace(vm->pid,
+                                              qemuDomainDetachDeviceUnlinkHelper,
+                                              (void *)file) < 0)
+                goto cleanup;
+        }
+    }
+
+    ret = 0;
+ cleanup:
+    return ret;
 }
 
 
@@ -8521,6 +8539,9 @@ qemuDomainNamespaceTeardownHostdev(virQEMUDriverPtr driver,
                                    virDomainObjPtr vm,
                                    virDomainHostdevDefPtr hostdev)
 {
+    virQEMUDriverConfigPtr cfg = NULL;
+    char **devMountsPath = NULL;
+    size_t ndevMountsPath = 0;
     int ret = -1;
     char **path = NULL;
     size_t i, npaths = 0;
@@ -8532,8 +8553,15 @@ qemuDomainNamespaceTeardownHostdev(virQEMUDriverPtr driver,
                                  &npaths, &path, NULL) < 0)
         goto cleanup;
 
+    cfg = virQEMUDriverGetConfig(driver);
+    if (qemuDomainGetPreservedMounts(cfg, vm,
+                                     &devMountsPath, NULL,
+                                     &ndevMountsPath) < 0)
+        goto cleanup;
+
     for (i = 0; i < npaths; i++) {
-        if (qemuDomainDetachDeviceUnlink(driver, vm, path[i]) < 0)
+        if (qemuDomainDetachDeviceUnlink(driver, vm, path[i],
+                                         devMountsPath, ndevMountsPath) < 0)
             goto cleanup;
     }
 
@@ -8542,6 +8570,8 @@ qemuDomainNamespaceTeardownHostdev(virQEMUDriverPtr driver,
     for (i = 0; i < npaths; i++)
         VIR_FREE(path[i]);
     VIR_FREE(path);
+    virStringListFreeCount(devMountsPath, ndevMountsPath);
+    virObjectUnref(cfg);
     return ret;
 }
 
@@ -8584,6 +8614,9 @@ qemuDomainNamespaceTeardownMemory(virQEMUDriverPtr driver,
                                   virDomainObjPtr vm,
                                   virDomainMemoryDefPtr mem)
 {
+    virQEMUDriverConfigPtr cfg = NULL;
+    char **devMountsPath = NULL;
+    size_t ndevMountsPath = 0;
     int ret = -1;
 
     if (mem->model != VIR_DOMAIN_MEMORY_MODEL_NVDIMM)
@@ -8592,10 +8625,19 @@ qemuDomainNamespaceTeardownMemory(virQEMUDriverPtr driver,
     if (!qemuDomainNamespaceEnabled(vm, QEMU_DOMAIN_NS_MOUNT))
         return 0;
 
-    if (qemuDomainDetachDeviceUnlink(driver, vm, mem->nvdimmPath) < 0)
+    cfg = virQEMUDriverGetConfig(driver);
+    if (qemuDomainGetPreservedMounts(cfg, vm,
+                                     &devMountsPath, NULL,
+                                     &ndevMountsPath) < 0)
+        goto cleanup;
+
+    if (qemuDomainDetachDeviceUnlink(driver, vm, mem->nvdimmPath,
+                                     devMountsPath, ndevMountsPath) < 0)
         goto cleanup;
     ret = 0;
  cleanup:
+    virStringListFreeCount(devMountsPath, ndevMountsPath);
+    virObjectUnref(cfg);
     return ret;
 }
 
@@ -8643,6 +8685,9 @@ qemuDomainNamespaceTeardownChardev(virQEMUDriverPtr driver,
                                    virDomainObjPtr vm,
                                    virDomainChrDefPtr chr)
 {
+    virQEMUDriverConfigPtr cfg = NULL;
+    char **devMountsPath = NULL;
+    size_t ndevMountsPath = 0;
     int ret = -1;
     const char *path = NULL;
 
@@ -8654,11 +8699,20 @@ qemuDomainNamespaceTeardownChardev(virQEMUDriverPtr driver,
 
     path = chr->source->data.file.path;
 
-    if (qemuDomainDetachDeviceUnlink(driver, vm, path) < 0)
+    cfg = virQEMUDriverGetConfig(driver);
+    if (qemuDomainGetPreservedMounts(cfg, vm,
+                                     &devMountsPath, NULL,
+                                     &ndevMountsPath) < 0)
+        goto cleanup;
+
+    if (qemuDomainDetachDeviceUnlink(driver, vm, path,
+                                     devMountsPath, ndevMountsPath) < 0)
         goto cleanup;
 
     ret = 0;
  cleanup:
+    virStringListFreeCount(devMountsPath, ndevMountsPath);
+    virObjectUnref(cfg);
     return ret;
 }
 
@@ -8712,6 +8766,9 @@ qemuDomainNamespaceTeardownRNG(virQEMUDriverPtr driver,
                                virDomainObjPtr vm,
                                virDomainRNGDefPtr rng)
 {
+    virQEMUDriverConfigPtr cfg = NULL;
+    char **devMountsPath = NULL;
+    size_t ndevMountsPath = 0;
     int ret = -1;
     const char *path = NULL;
 
@@ -8729,11 +8786,20 @@ qemuDomainNamespaceTeardownRNG(virQEMUDriverPtr driver,
         goto cleanup;
     }
 
-    if (qemuDomainDetachDeviceUnlink(driver, vm, path) < 0)
+    cfg = virQEMUDriverGetConfig(driver);
+    if (qemuDomainGetPreservedMounts(cfg, vm,
+                                     &devMountsPath, NULL,
+                                     &ndevMountsPath) < 0)
+        goto cleanup;
+
+    if (qemuDomainDetachDeviceUnlink(driver, vm, path,
+                                     devMountsPath, ndevMountsPath) < 0)
         goto cleanup;
 
     ret = 0;
  cleanup:
+    virStringListFreeCount(devMountsPath, ndevMountsPath);
+    virObjectUnref(cfg);
     return ret;
 }
 
-- 
2.10.2