Detect ld.so and libc.so version inconsistency during startup

The files NEWS, include/link.h, and sysdeps/generic/ldsodefs.h
contribute to the version fingerprint used for detection.  The
fingerprint can be further refined using the --with-extra-version-id
configure argument.

_dl_call_libc_early_init is replaced with _dl_lookup_libc_early_init.
The new function is used store a pointer to libc.so's
__libc_early_init function in the libc_map_early_init member of the
ld.so namespace structure.  This function pointer can then be called
directly, so the separate invocation function is no longer needed.

The versioned symbol lookup needs the symbol versioning data
structures, so the initialization of libc_map and libc_map_early_init
is now done from _dl_check_map_versions, after this information
becomes available.  (_dl_map_object_from_fd does not set this up
in time, so the initialization code had to be moved from there.)
This means that the separate initialization code can be removed from
dl_main because _dl_check_map_versions covers all maps, including
the initial executable loaded by the kernel.  The lookup still happens
before relocation and the invocation of IFUNC resolvers, so IFUNC
resolvers are protected from ABI mismatch.

The __libc_early_init function pointer is not protected because
so little code runs between the pointer write and the invocation
(only dynamic linker code and IFUNC resolvers).

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/elf/dl-version.c b/elf/dl-version.c
index cda0889..d9ec44e 100644
--- a/elf/dl-version.c
+++ b/elf/dl-version.c
@@ -23,6 +23,8 @@
 #include <string.h>
 #include <ldsodefs.h>
 #include <_itoa.h>
+#include <gnu/lib-names.h>
+#include <libc-early-init.h>
 
 #include <assert.h>
 
@@ -359,6 +361,22 @@ _dl_check_map_versions (struct link_map *map, int verbose, int trace_mode)
 	}
     }
 
+  /* Detect a libc.so loaded into this namespace.  The
+     __libc_early_init lookup below means that we have to do this
+     after parsing the version data.  */
+  if (GL(dl_ns)[map->l_ns].libc_map == NULL
+      && map->l_info[DT_SONAME] != NULL
+      && strcmp (((const char *) D_PTR (map, l_info[DT_STRTAB])
+		  + map->l_info[DT_SONAME]->d_un.d_val), LIBC_SO) == 0)
+    {
+      /* Look up this symbol early to trigger a mismatch error before
+	 relocation (which may call IFUNC resolvers, and those can
+	 have an internal ABI dependency).  */
+      GL(dl_ns)[map->l_ns].libc_map_early_init
+	= _dl_lookup_libc_early_init (map);
+      GL(dl_ns)[map->l_ns].libc_map = map;
+    }
+
   /* When there is a DT_VERNEED entry with libc.so on DT_NEEDED, issue
      an error if there is a DT_RELR entry without GLIBC_ABI_DT_RELR
      dependency.  */