[RFC][PATCH v7 13/20] Use the DSO search helper to check for preloaded DT_GNU_UNIQUE DSOs

["Vivek Das Mohapatra" <vivek@collabora.com>]

If a DSO already exists (with the same name) in the base namespace
and it is flagged DT_GNU_UNIQUE then we should behave as if a proxy
had been requested.
---
 elf/dl-open.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/elf/dl-open.c b/elf/dl-open.c
index a0f3233dd1..84f27dd1c6 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -484,6 +484,7 @@ dl_open_worker (void *a)
   const char *file = args->file;
   int mode = args->mode;
   struct link_map *call_map = NULL;
+  struct link_map *preloaded = NULL;
   int want_proxy = mode & RTLD_SHARED;
   Lmid_t proxy_ns = LM_ID_BASE;
 
@@ -532,6 +533,23 @@ dl_open_worker (void *a)
      may not be true if this is a recursive call to dlopen.  */
   _dl_debug_initialize (0, args->nsid);
 
+  /* Target Lmid is not the base and we haven't explicitly asked for a proxy:
+     We need to check for a matching DSO in the base Lmid in case it is flagged
+     DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE in which case we add RTLD_SHARED to the
+     mode and set want_proxy.
+     NOTE: RTLD_ISOLATE in the mode suppresses this behaviour.  */
+  if (__glibc_unlikely (args->nsid != LM_ID_BASE) &&
+      __glibc_likely (!want_proxy))
+    {
+      preloaded = _dl_find_dso (file, LM_ID_BASE);
+
+      if (preloaded && (preloaded->l_gnu_flags_1 & DF_GNU_1_UNIQUE))
+        {
+          want_proxy = RTLD_SHARED;
+          mode |= RTLD_SHARED;
+        }
+    }
+
   /* Load the named object.  */
   struct link_map *new;
   args->map = new = _dl_map_object (call_map, file, lt_loaded, 0,
-- 
2.20.1