libelf: Make sure version xlate dest buffer is fully defined.

https://bugzilla.redhat.com/show_bug.cgi?id=1170810#c16
contains an example of usage of undefined memory when version section
data needs to be translated, but the version xlate functions detect they
cannot fully transform the section data. To make sure the dest buffer
data is completely defined this patch makes sure all data is moved
from src to dest first. This is somewhat inefficient since normally
all data will be fully converted. But the translation functions have
no way to indicate only partial data was converted.

Reported-by: Alexander Cherepanov <[email protected]>
Signed-off-by: Mark Wielaard <[email protected]>

2 files changed, 16 insertions, 1 deletions

diff --git a/libelf/ChangeLog b/libelf/ChangeLog
index a1b0ee4a..e9c2a8de 100644
--- a/libelf/ChangeLog
+++ b/libelf/ChangeLog
@@ -1,3 +1,8 @@
+2015-01-03  Mark Wielaard  <[email protected]>
+
+	* version_xlate.h (elf_cvt_Verdef): Use memmove to copy src to dest.
+	(elf_cvt_Verneed): Likewise.
+
 2015-03-28  Mark Wielaard  <[email protected]>
 
 	* elf.h: Update from glibc.
diff --git a/libelf/version_xlate.h b/libelf/version_xlate.h
index 16eaa19c..9fe01c64 100644
--- a/libelf/version_xlate.h
+++ b/libelf/version_xlate.h
@@ -1,5 +1,5 @@
 /* Conversion functions for versioning information.
-   Copyright (C) 1998, 1999, 2000, 2002, 2003 Red Hat, Inc.
+   Copyright (C) 1998, 1999, 2000, 2002, 2003, 2015 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <[email protected]>, 1998.
 
@@ -55,6 +55,11 @@ elf_cvt_Verdef (void *dest, const void *src, size_t len, int encode)
   if (len == 0)
     return;
 
+  /* Below we rely on the next field offsets to be correct, start by
+     copying over all data as is in case some data isn't translated.
+     We don't want to leave (undefined) garbage in the dest buffer.  */
+  memmove (dest, src, len);
+
   do
     {
       size_t aux_offset;
@@ -149,6 +154,11 @@ elf_cvt_Verneed (void *dest, const void *src, size_t len, int encode)
   if (len == 0)
     return;
 
+  /* Below we rely on the next field offsets to be correct, start by
+     copying over all data as is in case some data isn't translated.
+     We don't want to leave (undefined) garbage in the dest buffer.  */
+  memmove (dest, src, len);
+
   do
     {
       size_t aux_offset;