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

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

[Mark Wielaard]

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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 <cherepan@mccme.ru>
Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 libelf/ChangeLog       |  5 +++++
 libelf/version_xlate.h | 12 +++++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/libelf/ChangeLog b/libelf/ChangeLog
index 2ca9509..adfccf1 100644
--- a/libelf/ChangeLog
+++ b/libelf/ChangeLog
@@ -1,3 +1,8 @@
+2015-01-03  Mark Wielaard  <mjw@redhat.com>
+
+	* version_xlate.h (elf_cvt_Verdef): Use memmove to copy src to dest.
+	(elf_cvt_Verneed): Likewise.
+
 2014-12-30  Mark Wielaard  <mjw@redhat.com>
 
 	* elf_getphdrnum.c (__elf_getphdrnum_chk_rdlock): New function.
diff --git a/libelf/version_xlate.h b/libelf/version_xlate.h
index 16eaa19..9fe01c6 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 <drepper@redhat.com>, 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;
-- 
2.1.0

Re: [PATCH] libelf: Make sure version xlate dest buffer is fully defined.

[Mark Wielaard]

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On Sat, 2015-01-03 at 23:02 +0100, Mark Wielaard wrote:
> 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 <cherepan@mccme.ru>
> Signed-off-by: Mark Wielaard <mjw@redhat.com>
>
> --- a/libelf/ChangeLog
> +++ b/libelf/ChangeLog
> @@ -1,3 +1,8 @@
> +2015-01-03  Mark Wielaard  <mjw@redhat.com>
> +
> +	* version_xlate.h (elf_cvt_Verdef): Use memmove to copy src to dest.
> +	(elf_cvt_Verneed): Likewise.

I have finally pushed this to master.
I don't particularly like this solution. But the extra work is only done
when doing conversion of version data representation of the ELF file on
disk is different from the native data representation in memory.

Cheers,

Mark