[libvirt] [PATCH] qemu: Be more selective when determining cdrom for taint messaging

[John Ferlan]

https://bugzilla.redhat.com/show_bug.cgi?id=1471225

Commit id '99a2d6af2' was a bit too aggressive with determining whether
the provided path was a "physical" cd-rom in order to generate a taint
message due to the possibility of some guest and host trying to control
the tray. For cd-rom guest devices backed to some VIR_STORAGE_TYPE_FILE
storage, this wouldn't be a problem and as such it shouldn't be a problem
for guest devices using some sort of block device on the host such as
iSCSI, LVM, or a Disk pool would present.

Signed-off-by: John Ferlan <jferlan at redhat.com>
---
 src/libvirt_private.syms |  1 +
 src/qemu/qemu_domain.c   |  2 +-
 src/util/virfile.c       | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/util/virfile.h       |  4 ++++
 4 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index f30a04b..0354568 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1680,6 +1680,7 @@ virFileGetMountSubtree;
 virFileHasSuffix;
 virFileInData;
 virFileIsAbsPath;
+virFileIsCDROM;
 virFileIsDir;
 virFileIsExecutable;
 virFileIsLink;
diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 9cff501..426c577 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -4807,7 +4807,7 @@ void qemuDomainObjCheckDiskTaint(virQEMUDriverPtr driver,
 
     if (disk->device == VIR_DOMAIN_DISK_DEVICE_CDROM &&
         virStorageSourceGetActualType(disk->src) == VIR_STORAGE_TYPE_BLOCK &&
-        disk->src->path)
+        disk->src->path && virFileIsCDROM(disk->src->path))
         qemuDomainObjTaint(driver, obj, VIR_DOMAIN_TAINT_CDROM_PASSTHROUGH,
                            logCtxt);
 
diff --git a/src/util/virfile.c b/src/util/virfile.c
index 2f28e83..4c31949 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -4166,3 +4166,51 @@ virFileReadValueString(char **value, const char *format, ...)
     VIR_FREE(str);
     return ret;
 }
+
+
+#if defined(__linux__)
+
+/* virFileIsCDROM
+ * @path: Supplied path.
+ *
+ * Determine if the path is a CD-ROM path. Typically on Linux systems this
+ * is either /dev/cdrom or /dev/sr0, so those are easy checks. Still if
+ * someone is trying to be tricky, we can resolve the link to /dev/cdrom
+ * and compare it to the resolved link of the supplied @path to compare
+ * if they're the same.
+ *
+ * Returns true if the path is a CDROM, false otherwise.
+ */
+bool
+virFileIsCDROM(const char *path)
+{
+    bool ret = false;
+    char *linkpath = NULL;
+    char *cdrompath = NULL;
+
+    if (STREQ(path, "/dev/cdrom") || STREQ(path, "/dev/sr0"))
+        return true;
+
+    if (virFileResolveLink(path, &linkpath) < 0 ||
+        virFileResolveLink("/dev/cdrom", &cdrompath) < 0)
+        goto cleanup;
+
+    ret = STREQ(linkpath, cdrompath);
+
+ cleanup:
+    VIR_FREE(linkpath);
+    VIR_FREE(cdrompath);
+    return ret;
+}
+
+#else /* __linux__ */
+
+bool
+virFileIsCDROM(const char *path)
+{
+    /* XXX implement me :-) */
+    virReportUnsupportedError();
+    return false;
+}
+
+#endif /* __linux__ */
diff --git a/src/util/virfile.h b/src/util/virfile.h
index 57ceb80..21caabf 100644
--- a/src/util/virfile.h
+++ b/src/util/virfile.h
@@ -352,4 +352,8 @@ int virFileInData(int fd,
                   int *inData,
                   long long *length);
 
+bool
+virFileIsCDROM(const char *path)
+    ATTRIBUTE_NONNULL(1);
+
 #endif /* __VIR_FILE_H */
-- 
2.9.5