[PATCH] virDevMapperGetTargetsImpl: quit early if device is not a devmapper target

[Michal Privoznik]

As suggested in the linked bug, libvirt should firstly check
whether the major number of the device is device mapper major.
Because if it isn't subsequent DM_DEVICE_DEPS task may not only
fail, but also yield different results. In the bugzilla this is
demonstrated by creating a devmapper target named 'loop0' and
then creating loop target /dev/loop0. When the latter is then
passed to a domain, our virDevMapperGetTargetsImpl() function
blindly asks devmapper to provide target dependencies for
/dev/loop0 and because of the way devmapper APIs work, it will
'sanitize' the input by using the last component only which is
'loop0' and thus return different results than expected.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1823976

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/util/virdevmapper.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/util/virdevmapper.c b/src/util/virdevmapper.c
index feb5982315..ee026d502e 100644
--- a/src/util/virdevmapper.c
+++ b/src/util/virdevmapper.c
@@ -64,6 +64,7 @@ virDevMapperGetTargetsImpl(const char *path,
                            char ***devPaths_ret,
                            unsigned int ttl)
 {
+    struct stat sb;
     struct dm_task *dmt = NULL;
     struct dm_deps *deps;
     struct dm_info info;
@@ -82,6 +83,15 @@ virDevMapperGetTargetsImpl(const char *path,
         return ret;
     }
 
+    if (stat(path, &sb) < 0) {
+        if (errno == ENOENT)
+            ret = 0;
+        return ret;
+    }
+
+    if (!dm_is_dm_major(major(sb.st_dev)))
+        return 0;
+
     if (!(dmt = dm_task_create(DM_DEVICE_DEPS))) {
         if (errno == ENOENT || errno == ENODEV) {
             /* It's okay. Kernel is probably built without
-- 
2.26.2