[PATCH v3 2/2] nss: handle stat failure in check_reload_and_get (BZ #28752)

[Sam James <sam@gentoo.org>]

Skip the chroot test if the database isn't loaded
correctly (because the chroot test uses some
existing DB state).

The __stat64_time64 -> fstatat call can fail if
running under an (aggressive) seccomp filter,
like Firefox seems to use.

This manifested in a crash when using glib built
with FAM support with such a Firefox build.

Suggested-by: DJ Delorie <dj@redhat.com>
Signed-off-by: Sam James <sam@gentoo.org>
---
 nss/nss_database.c | 38 +++++++++++++++++++++-----------------
 1 file changed, 21 insertions(+), 17 deletions(-)

diff --git a/nss/nss_database.c b/nss/nss_database.c
index d56c5b798d..4ff9bf5696 100644
--- a/nss/nss_database.c
+++ b/nss/nss_database.c
@@ -420,23 +420,27 @@ nss_database_check_reload_and_get (struct nss_database_state *local,
       return true;
     }
 
-  /* Before we reload, verify that "/" hasn't changed.  We assume that
-     errors here are very unlikely, but the chance that we're entering
-     a container is also very unlikely, so we err on the side of both
-     very unlikely things not happening at the same time.  */
-  if (__stat64_time64 ("/", &str) != 0
-      || (local->root_ino != 0
-	  && (str.st_ino != local->root_ino
-	      ||  str.st_dev != local->root_dev)))
-    {
-      /* Change detected; disable reloading and return current state.  */
-      atomic_store_release (&local->data.reload_disabled, 1);
-      *result = local->data.services[database_index];
-      __libc_lock_unlock (local->lock);
-      return true;
-    }
-  local->root_ino = str.st_ino;
-  local->root_dev = str.st_dev;
+  if (local->data.services[database_index] != NULL) {
+      /* Before we reload, verify that "/" hasn't changed.  We assume that
+        errors here are very unlikely, but the chance that we're entering
+        a container is also very unlikely, so we err on the side of both
+        very unlikely things not happening at the same time.  */
+      if (__stat64_time64 ("/", &str) != 0
+        || (local->root_ino != 0
+        && (str.st_ino != local->root_ino
+            ||  str.st_dev != local->root_dev)))
+      {
+        /* Change detected; disable reloading and return current state.  */
+        atomic_store_release (&local->data.reload_disabled, 1);
+        *result = local->data.services[database_index];
+        __libc_lock_unlock (local->lock);
+        return true;
+      }
+
+    local->root_ino = str.st_ino;
+    local->root_dev = str.st_dev;
+  }
+
   __libc_lock_unlock (local->lock);
 
   /* Avoid overwriting the global configuration until we have loaded
-- 
2.35.1