[RFC][PATCH v6 11/20] Compare loaded DSOs by file ID and check for DF_GNU_1_UNIQUE

[Vivek Das Mohapatra]

If _dl_map_object_from_fd finds that a DSO it was asked to
load into a non-base namespace is already loaded (into the
main namespace) and is flagged DF_GNU_1_UNIQUE then it should
return that DSO's link map entry.

In such cases _dl_open_worker must notice that this has
happened and dontinue down the link map proxy generation
path instead of normal link map entry preparation.
---
 elf/dl-load.c | 26 ++++++++++++++++++++++++++
 elf/dl-open.c | 10 ++++++++++
 2 files changed, 36 insertions(+)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 3fda5de71b..0e6a493e07 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1020,6 +1020,32 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
     }
 #endif
 
+  /* DSOs in the main namespace which are flagged DF_GNU_1_UNIQUE should only
+     be opened into the main namespace. Other namespaces should only get
+     proxies.  */
+  if (__glibc_unlikely (nsid != LM_ID_BASE))
+    {
+      /* Check base ns to see if the name matched another already loaded.  */
+      for (l = GL(dl_ns)[LM_ID_BASE]._ns_loaded; l != NULL; l = l->l_next)
+        if (!l->l_removed && _dl_file_id_match_p (&l->l_file_id, &id))
+          {
+            if (!(l->l_gnu_flags_1 & DF_GNU_1_UNIQUE))
+              continue;
+
+            /* Already loaded. Bump its reference count and return it.  */
+            __close_nocancel (fd);
+
+            /* If the name is not listed for this object add it.  */
+            free (realname);
+            add_name_to_object (l, name);
+
+            /* NOTE: It is important that our caller picks up on the fact
+               that we have NOT returned an object in the requested namespace
+               and handles the proxying correctly */
+            return l;
+          }
+    }
+
   if (mode & RTLD_NOLOAD)
     {
       /* We are not supposed to load the object unless it is already
diff --git a/elf/dl-open.c b/elf/dl-open.c
index 02e094a867..a0f3233dd1 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -561,6 +561,16 @@ dl_open_worker (void *a)
       return;
     }
 
+  /* If we are trying to load a DF_GNU_1_UNIQUE flagged DSO which was
+     NOT ALREADY LOADED (or not loaded with the name we are using) then
+     _dl_map_object will have returned an instance from the main namespace.
+     We need to detect this and set up the RTLD_SHARED flags.  */
+  if (__glibc_unlikely(args->nsid != LM_ID_BASE && new->l_ns == LM_ID_BASE))
+    {
+      want_proxy = RTLD_SHARED;
+      mode |= RTLD_SHARED;
+    }
+
   /* If we want proxy and we get this far then the entry in ‘new’ will
      be in the main namespace: we should revert to the main namespace code
      path(s), but remember the namespace we want the proxy to be in.  */
-- 
2.20.1