[PATCH] libdw: Handle NULL dbg for call_ref, GNU_implicit_pointer and addr DW_OPs.

[PATCH] libdw: Handle NULL dbg for call_ref, GNU_implicit_pointer and addr DW_OPs.

[Mark Wielaard]

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afl-fuzz pointed out that __libdw_intern_expression didn't handle CFI
containing DW_OP_call_ref, DW_OP_implicit_pointer or DW_OP_addr. Because
in that case the Dwarf dbg is NULL. Both DW_OP_call_ref and
DW_OP_implicit_pointer cannot be used in CFI. That is just an error.
But DW_OP_addr can be. Without a Dwarf dbg we'll need to read the address
argument directly. Don't use __libdw_read_address_inc which might do a
relocation of the value read. But in practice the relocation hook isn't
implemented anyway.

Signed-off-by: Mark Wielaard <mjw@redhat.com>
---
 libdw/ChangeLog           |  6 ++++++
 libdw/dwarf_getlocation.c | 42 ++++++++++++++++++++++++++++++++----------
 2 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 0e7e7a3..dd11755 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,9 @@
+2015-01-02  Mark Wielaard  <mjw@redhat.com>
+
+	* dwarf_getlocation.c (__libdw_intern_expression): Check dbg is not
+	NULL for DW_OP_call_ref and DW_OP_GNU_implicit_pointer. For
+	DW_OP_addr if dbg is NULL then read argument directly.
+
 2014-12-24  Mark Wielaard  <mjw@redhat.com>
 
 	* dwarf_getsrc_die.c (dwarf_getsrc_die): Return the last line record
diff --git a/libdw/dwarf_getlocation.c b/libdw/dwarf_getlocation.c
index 068f385..a3a5bd4 100644
--- a/libdw/dwarf_getlocation.c
+++ b/libdw/dwarf_getlocation.c
@@ -1,5 +1,5 @@
 /* Return location expression list.
-   Copyright (C) 2000-2010, 2013, 2014 Red Hat, Inc.
+   Copyright (C) 2000-2010, 2013-2015 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2000.
 
@@ -270,16 +270,36 @@ __libdw_intern_expression (Dwarf *dbg, bool other_byte_order,
 	{
 	case DW_OP_addr:
 	  /* Address, depends on address size of CU.  */
-	  if (__libdw_read_address_inc (dbg, sec_index, &data,
-					address_size, &newloc->number))
-	    return -1;
+	  if (dbg == NULL)
+	    {
+	      // XXX relocation?
+	      if (address_size == 4)
+		{
+		  if (unlikely (data + 4 > end_data))
+		    goto invalid;
+		  else
+		    newloc->number = read_4ubyte_unaligned_inc (&bo, data);
+		}
+	      else
+		{
+		  if (unlikely (data + 8 > end_data))
+		    goto invalid;
+		  else
+		    newloc->number = read_8ubyte_unaligned_inc (&bo, data);
+		}
+	    }
+	  else if (__libdw_read_address_inc (dbg, sec_index, &data,
+					     address_size, &newloc->number))
+	    goto invalid;
 	  break;
 
 	case DW_OP_call_ref:
 	  /* DW_FORM_ref_addr, depends on offset size of CU.  */
-	  if (__libdw_read_offset_inc (dbg, sec_index, &data, ref_size,
-				       &newloc->number, IDX_debug_info, 0))
-	    return -1;
+	  if (dbg == NULL || __libdw_read_offset_inc (dbg, sec_index, &data,
+						      ref_size,
+						      &newloc->number,
+						      IDX_debug_info, 0))
+	    goto invalid;
 	  break;
 
 	case DW_OP_deref:
@@ -435,9 +455,11 @@ __libdw_intern_expression (Dwarf *dbg, bool other_byte_order,
 
 	case DW_OP_GNU_implicit_pointer:
 	  /* DW_FORM_ref_addr, depends on offset size of CU.  */
-	  if (__libdw_read_offset_inc (dbg, sec_index, &data, ref_size,
-				       &newloc->number, IDX_debug_info, 0))
-	    return -1;
+	  if (dbg == NULL || __libdw_read_offset_inc (dbg, sec_index, &data,
+						      ref_size,
+						      &newloc->number,
+						      IDX_debug_info, 0))
+	    goto invalid;
 	  if (unlikely (data >= end_data))
 	    goto invalid;
 	  get_uleb128 (newloc->number2, data, end_data); /* Byte offset.  */
-- 
2.1.0

Re: [PATCH] libdw: Handle NULL dbg for call_ref, GNU_implicit_pointer and addr DW_OPs.

[Mark Wielaard]

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On Sat, 2015-01-03 at 00:25 +0100, Mark Wielaard wrote:
> afl-fuzz pointed out that __libdw_intern_expression didn't handle CFI
> containing DW_OP_call_ref, DW_OP_implicit_pointer or DW_OP_addr. Because
> in that case the Dwarf dbg is NULL. Both DW_OP_call_ref and
> DW_OP_implicit_pointer cannot be used in CFI. That is just an error.
> But DW_OP_addr can be. Without a Dwarf dbg we'll need to read the address
> argument directly. Don't use __libdw_read_address_inc which might do a
> relocation of the value read. But in practice the relocation hook isn't
> implemented anyway.
> 
> Signed-off-by: Mark Wielaard <mjw@redhat.com>

I pushed this to master.