[2.28 COMMITTED] elf: Refuse to dlopen PIE objects [BZ #24323]

[DJ Delorie <dj@redhat.com>]

From: Florian Weimer <fweimer@redhat.com>

Another executable has already been mapped, so the dynamic linker
cannot perform relocations correctly for the second executable.

(cherry picked from commit 2c75b545de6fe3c44138799c68217a94bc669a88)
(test omitted due to indirect dependency on test-in-container)

diff --git a/ChangeLog b/ChangeLog
index d932485496..37553b12e7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2019-06-18  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #24323]
+	* include/elf.h (DT_1_SUPPORTED_MASK): Include DF_1_PIE.
+	* elf/dl-load.c (_dl_map_object_from_fd): Check for DF_1_PIE and
+	fail when called from dlopen.
+
 2019-07-10  DJ Delorie  <dj@redhat.com>
 	    Sergei Trofimovich <slyfox@inbox.ru>
 
diff --git a/elf/dl-load.c b/elf/dl-load.c
index c51e4b3718..162a78cb0d 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1173,6 +1173,10 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	goto call_lose;
       }
 
+    /* dlopen of an executable is not valid because it is not possible
+       to perform proper relocations, handle static TLS, or run the
+       ELF constructors.  For PIE, the check needs the dynamic
+       section, so there is another check below.  */
     if (__glibc_unlikely (type != ET_DYN)
 	&& __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0))
       {
@@ -1209,9 +1213,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
   elf_get_dynamic_info (l, NULL);
 
   /* Make sure we are not dlopen'ing an object that has the
-     DF_1_NOOPEN flag set.  */
-  if (__glibc_unlikely (l->l_flags_1 & DF_1_NOOPEN)
-      && (mode & __RTLD_DLOPEN))
+     DF_1_NOOPEN flag set, or a PIE object.  */
+  if ((__glibc_unlikely (l->l_flags_1 & DF_1_NOOPEN)
+       && (mode & __RTLD_DLOPEN))
+      || (__glibc_unlikely (l->l_flags_1 & DF_1_PIE)
+	  && __glibc_unlikely ((mode & __RTLD_OPENEXEC) == 0)))
     {
       /* We are not supposed to load this object.  Free all resources.  */
       _dl_unmap_segments (l);
@@ -1222,7 +1228,11 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
       if (l->l_phdr_allocated)
 	free ((void *) l->l_phdr);
 
-      errstring = N_("shared object cannot be dlopen()ed");
+      if (l->l_flags_1 & DF_1_PIE)
+	errstring
+	  = N_("cannot dynamically load position-independent executable");
+      else
+	errstring = N_("shared object cannot be dlopen()ed");
       goto call_lose;
     }
 
diff --git a/include/elf.h b/include/elf.h
index ab76aafb1e..14ed67ff67 100644
--- a/include/elf.h
+++ b/include/elf.h
@@ -23,7 +23,7 @@
 # endif
 # define DT_1_SUPPORTED_MASK \
    (DF_1_NOW | DF_1_NODELETE | DF_1_INITFIRST | DF_1_NOOPEN \
-    | DF_1_ORIGIN | DF_1_NODEFLIB)
+    | DF_1_ORIGIN | DF_1_NODEFLIB | DF_1_PIE)
 
 #endif /* !_ISOMAC */
 #endif /* elf.h */