commit 64aef5fb9afecc023a6e719da161dbbf450908b8
Author: Jim Meyering <jim@meyering.net>
Date:   Tue Oct 16 17:43:49 2012 +0200

    cp: avoid data-corrupting free-memory-read

    NEWS entry:
    cp could read from freed memory and could even make corrupt copies.
    This could happen with a very fragmented and sparse input file,
    on GNU/Linux file systems supporting fiemap extent scanning.
    This bug also affects mv when it resorts to copying, and install.
    [bug introduced in coreutils-8.11]

    * src/extent-scan.c (extent_scan_read): Reset our last_ei
    pointer whenever the parent buffer might have just been freed.
    * tests/cp/fiemap-extent-FMR.sh: New test.
    * tests/local.mk (all_tests): Add it.
    * NEWS (Bug fixes): Mention it.
    Reported by Mike Gerth in http://bugs.gnu.org/12656, and with
    help from Alan Curry.  Bug introduced in commit v8.10-60-g18f5a85.

Index: src/extent-scan.c
===================================================================
--- src/extent-scan.c.orig
+++ src/extent-scan.c
@@ -89,7 +89,7 @@ extern bool
 extent_scan_read (struct extent_scan *scan)
 {
   unsigned int si = 0;
-  struct extent_info *last_ei IF_LINT ( = scan->ext_info);
+  struct extent_info *last_ei = scan->ext_info;
 
   while (true)
     {
@@ -127,8 +127,14 @@ extent_scan_read (struct extent_scan *sc
 
       assert (scan->ei_count <= SIZE_MAX - fiemap->fm_mapped_extents);
       scan->ei_count += fiemap->fm_mapped_extents;
-      scan->ext_info = xnrealloc (scan->ext_info, scan->ei_count,
-                                  sizeof (struct extent_info));
+      {
+        /* last_ei points into a buffer that may be freed via xnrealloc.
+           Record its offset and adjust after allocation.  */
+        size_t prev_idx = last_ei - scan->ext_info;
+        scan->ext_info = xnrealloc (scan->ext_info, scan->ei_count,
+                                    sizeof (struct extent_info));
+        last_ei = scan->ext_info + prev_idx;
+      }
 
       unsigned int i = 0;
       for (i = 0; i < fiemap->fm_mapped_extents; i++)
Index: tests/cp/fiemap-FMR
===================================================================
--- /dev/null
+++ tests/cp/fiemap-FMR
@@ -0,0 +1,31 @@
+#!/bin/sh
+# Trigger a free-memory read bug in cp from coreutils-[8.11..8.19]
+
+# Copyright (C) 2012 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/init.sh"; path_prepend_ ./src
+print_ver_ cp
+
+require_valgrind_
+require_perl_
+: ${PERL=perl}
+
+$PERL -e 'for (1..600) { sysseek (*STDOUT, 4096, 1)' \
+  -e '&& syswrite (*STDOUT, "a" x 1024) or die "$!"}' > j || fail=1
+valgrind --quiet --error-exitcode=3 cp j j2 || fail=1
+cmp j j2 || fail=1
+
+Exit $fail
Index: tests/Makefile.am
===================================================================
--- tests/Makefile.am.orig
+++ tests/Makefile.am
@@ -342,6 +342,7 @@ TESTS =						\
   cp/existing-perm-race				\
   cp/fail-perm					\
   cp/fiemap-empty                               \
+  cp/fiemap-FMR                                 \
   cp/fiemap-perf                                \
   cp/fiemap-2                                   \
   cp/file-perm-race				\