[PATCH v2 06/32] elf: Remove version assert in check_match in elf/dl-lookup.c

[Florian Weimer <fweimer@redhat.com>]

This case is detected early in the elf/dl-versionc.c consistency
checks.  (These checks could be disabled in the future to allow
the removal of symbol versioning from objects.)

Commit f0b2132b35 ("ld.so: Support moving versioned symbols between
sonames [BZ #24741]) removed another call to _dl_name_match_p.  The
_dl_check_caller function no longer exists, and the remaining calls
to _dl_name_match_p happen under the loader lock.  This means that
atomic accesses are no longer required for the l_libname list.  This
supersedes commit 395be7c218 ("elf: Fix data race in _dl_name_match_p
[BZ #21349]").
---
 elf/dl-load.c   | 18 +-----------------
 elf/dl-lookup.c | 19 +++----------------
 elf/dl-misc.c   |  4 +---
 3 files changed, 5 insertions(+), 36 deletions(-)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 58c5dc7355..9a9cee599d 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -439,23 +439,7 @@ add_name_to_object (struct link_map *l, const char *name)
   newname->name = memcpy (newname + 1, name, name_len);
   newname->next = NULL;
   newname->dont_free = 0;
-  /* CONCURRENCY NOTES:
-
-     Make sure the initialization of newname happens before its address is
-     read from the lastp->next store below.
-
-     GL(dl_load_lock) is held here (and by other writers, e.g. dlclose), so
-     readers of libname_list->next (e.g. _dl_check_caller or the reads above)
-     can use that for synchronization, however the read in _dl_name_match_p
-     may be executed without holding the lock during _dl_runtime_resolve
-     (i.e. lazy symbol resolution when a function of library l is called).
-
-     The release MO store below synchronizes with the acquire MO load in
-     _dl_name_match_p.  Other writes need to synchronize with that load too,
-     however those happen either early when the process is single threaded
-     (dl_main) or when the library is unloaded (dlclose) and the user has to
-     synchronize library calls with unloading.  */
-  atomic_store_release (&lastp->next, newname);
+  lastp->next = newname;
 }
 
 /* Standard search directories.  */
diff --git a/elf/dl-lookup.c b/elf/dl-lookup.c
index a8f48fed12..52decf616d 100644
--- a/elf/dl-lookup.c
+++ b/elf/dl-lookup.c
@@ -94,22 +94,9 @@ check_match (const char *const undef_name,
   const ElfW(Half) *verstab = map->l_versyms;
   if (version != NULL)
     {
-      if (__glibc_unlikely (verstab == NULL))
-	{
-	  /* We need a versioned symbol but haven't found any.  If
-	     this is the object which is referenced in the verneed
-	     entry it is a bug in the library since a symbol must
-	     not simply disappear.
-
-	     It would also be a bug in the object since it means that
-	     the list of required versions is incomplete and so the
-	     tests in dl-version.c haven't found a problem.*/
-	  assert (version->filename == NULL
-		  || ! _dl_name_match_p (version->filename, map));
-
-	  /* Otherwise we accept the symbol.  */
-	}
-      else
+      /* If there is no version information, accept the symbol.  This
+	 can happen during symbol interposition.  */
+      if (__glibc_likely (verstab != NULL))
 	{
 	  /* We can match the version information or use the
 	     default one if it is not hidden.  */
diff --git a/elf/dl-misc.c b/elf/dl-misc.c
index 5b84adc2f4..e998083284 100644
--- a/elf/dl-misc.c
+++ b/elf/dl-misc.c
@@ -75,9 +75,7 @@ _dl_name_match_p (const char *name, const struct link_map *map)
     if (strcmp (name, runp->name) == 0)
       return 1;
     else
-      /* Synchronize with the release MO store in add_name_to_object.
-	 See CONCURRENCY NOTES in add_name_to_object in dl-load.c.  */
-      runp = atomic_load_acquire (&runp->next);
+      runp = runp->next;
 
   return 0;
 }
-- 
2.41.0