x86: Check IFUNC definition in unrelocated executable [BZ #20019]

Calling an IFUNC function defined in unrelocated executable also leads to
segfault.  Issue a fatal error message when calling IFUNC function defined
in the unrelocated executable from a shared library.

On x86, ifuncmain6pie failed with:

[hjl@gnu-cfl-2 build-i686-linux]$ ./elf/ifuncmain6pie --direct
./elf/ifuncmain6pie: IFUNC symbol 'foo' referenced in '/export/build/gnu/tools-build/glibc-32bit/build-i686-linux/elf/ifuncmod6.so' is defined in the executable and creates an unsatisfiable circular dependency.
[hjl@gnu-cfl-2 build-i686-linux]$ readelf -rW elf/ifuncmod6.so | grep foo
00003ff4  00000706 R_386_GLOB_DAT         0000400c   foo_ptr
00003ff8  00000406 R_386_GLOB_DAT         00000000   foo
0000400c  00000401 R_386_32               00000000   foo
[hjl@gnu-cfl-2 build-i686-linux]$

Remove non-JUMP_SLOT relocations against foo in ifuncmod6.so, which
trigger the circular IFUNC dependency, and build ifuncmain6pie with
-Wl,-z,lazy.

(cherry picked from commits 6ea5b57afa5cdc9ce367d2b69a2cebfb273e4617
 and 7137d682ebfcb6db5dfc5f39724718699922f06c)

diff --git a/NEWS b/NEWS
index 8b589b175b0a59d638de06128ebdf780cb385503..f2780415121fd9d4b8673e38a9384e13345ebae1 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,7 @@ using `glibc' in the "product" field.
 \f
 The following bugs are resolved with this release:
 
+  [20019] NULL pointer dereference in libc.so.6 IFUNC due to uninitialized GOT
   [26224] iconv hangs when converting some invalid inputs from several IBM
     character sets (CVE-2020-27618)
   [26534] libm.so 2.32 SIGILL in pow() due to FMA4 instruction on non-FMA4

diff --git a/elf/Makefile b/elf/Makefile
index 0b78721848b9317b6c542da965f847282ea29af1..355e70037b5b6ed2130841f4b80c0cc06db36903 100644 (file)
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -1381,6 +1381,8 @@ CFLAGS-ifuncmain7pie.c += $(pie-ccflag)
 CFLAGS-ifuncmain9pie.c += $(pie-ccflag)
 CFLAGS-tst-ifunc-textrel.c += $(pic-ccflag)
 
+LDFLAGS-ifuncmain6pie = -Wl,-z,lazy
+
 $(objpfx)ifuncmain1pie: $(objpfx)ifuncmod1.so
 $(objpfx)ifuncmain1staticpie: $(objpfx)ifuncdep1pic.o
 $(objpfx)ifuncmain1vispie: $(objpfx)ifuncmod1.so

diff --git a/elf/ifuncmain6pie.c b/elf/ifuncmain6pie.c
index 04faeb86ef999019f42fa1843d52edaecd9ca00d..4a01906836173e3a2e1a5a87b1d20dc793f48beb 100644 (file)
--- a/elf/ifuncmain6pie.c
+++ b/elf/ifuncmain6pie.c
@@ -9,7 +9,6 @@
 #include "ifunc-sel.h"
 
 typedef int (*foo_p) (void);
-extern foo_p foo_ptr;
 
 static int
 one (void)
@@ -28,20 +27,17 @@ foo_ifunc (void)
 }
 
 extern int foo (void);
-extern foo_p get_foo (void);
+extern int call_foo (void);
 extern foo_p get_foo_p (void);
 
-foo_p my_foo_ptr = foo;
+foo_p foo_ptr = foo;
 
 int
 main (void)
 {
   foo_p p;
 
-  p = get_foo ();
-  if (p != foo)
-    abort ();
-  if ((*p) () != -30)
+  if (call_foo () != -30)
     abort ();
 
   p = get_foo_p ();
@@ -52,12 +48,8 @@ main (void)
 
   if (foo_ptr != foo)
     abort ();
-  if (my_foo_ptr != foo)
-    abort ();
   if ((*foo_ptr) () != -30)
     abort ();
-  if ((*my_foo_ptr) () != -30)
-    abort ();
   if (foo () != -30)
     abort ();
 

diff --git a/elf/ifuncmod6.c b/elf/ifuncmod6.c
index 2e16c1d06d065aa071352376a1338488ab01d344..2f6d0715e6e9ff992323ca436c12ac5037d51055 100644 (file)
--- a/elf/ifuncmod6.c
+++ b/elf/ifuncmod6.c
@@ -4,7 +4,7 @@ extern int foo (void);
 
 typedef int (*foo_p) (void);
 
-foo_p foo_ptr = foo;
+extern foo_p foo_ptr;
 
 foo_p
 get_foo_p (void)
@@ -12,8 +12,8 @@ get_foo_p (void)
   return foo_ptr;
 }
 
-foo_p
-get_foo (void)
+int
+call_foo (void)
 {
-  return foo;
+  return foo ();
 }

diff --git a/sysdeps/i386/dl-machine.h b/sysdeps/i386/dl-machine.h
index 0f08079e48a296ed10f19639ddf1a18874c1c589..672d8f27cef4b51502f14537edc529f9a0e4a209 100644 (file)
--- a/sysdeps/i386/dl-machine.h
+++ b/sysdeps/i386/dl-machine.h
@@ -338,16 +338,22 @@ elf_machine_rel (struct link_map *map, const Elf32_Rel *reloc,
        {
 # ifndef RTLD_BOOTSTRAP
          if (sym_map != map
-             && sym_map->l_type != lt_executable
              && !sym_map->l_relocated)
            {
              const char *strtab
                = (const char *) D_PTR (map, l_info[DT_STRTAB]);
-             _dl_error_printf ("\
+             if (sym_map->l_type == lt_executable)
+               _dl_fatal_printf ("\
+%s: IFUNC symbol '%s' referenced in '%s' is defined in the executable \
+and creates an unsatisfiable circular dependency.\n",
+                                 RTLD_PROGNAME, strtab + refsym->st_name,
+                                 map->l_name);
+             else
+               _dl_error_printf ("\
 %s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
-                               RTLD_PROGNAME, map->l_name,
-                               sym_map->l_name,
-                               strtab + refsym->st_name);
+                                 RTLD_PROGNAME, map->l_name,
+                                 sym_map->l_name,
+                                 strtab + refsym->st_name);
            }
 # endif
          value = ((Elf32_Addr (*) (void)) value) ();

diff --git a/sysdeps/x86_64/dl-machine.h b/sysdeps/x86_64/dl-machine.h
index ca73d8fef9c11aa814d0f89acbb064e770caec95..363a749cb2f20426467a99a85ee46ffa75c4eedc 100644 (file)
--- a/sysdeps/x86_64/dl-machine.h
+++ b/sysdeps/x86_64/dl-machine.h
@@ -315,16 +315,22 @@ elf_machine_rela (struct link_map *map, const ElfW(Rela) *reloc,
        {
 # ifndef RTLD_BOOTSTRAP
          if (sym_map != map
-             && sym_map->l_type != lt_executable
              && !sym_map->l_relocated)
            {
              const char *strtab
                = (const char *) D_PTR (map, l_info[DT_STRTAB]);
-             _dl_error_printf ("\
+             if (sym_map->l_type == lt_executable)
+               _dl_fatal_printf ("\
+%s: IFUNC symbol '%s' referenced in '%s' is defined in the executable \
+and creates an unsatisfiable circular dependency.\n",
+                                 RTLD_PROGNAME, strtab + refsym->st_name,
+                                 map->l_name);
+             else
+               _dl_error_printf ("\
 %s: Relink `%s' with `%s' for IFUNC symbol `%s'\n",
-                               RTLD_PROGNAME, map->l_name,
-                               sym_map->l_name,
-                               strtab + refsym->st_name);
+                                 RTLD_PROGNAME, map->l_name,
+                                 sym_map->l_name,
+                                 strtab + refsym->st_name);
            }
 # endif
          value = ((ElfW(Addr) (*) (void)) value) ();