From 6ad3791f095cfc1b0294f62c4b3a524ba735595e Mon Sep 17 00:00:00 2001
From: Sandra Loosemore <sandra@codesourcery.com>
Date: Thu, 25 Apr 2019 07:27:02 -0700
Subject: [PATCH] Detect invalid length field in debug frame FDE header.

GDB was failing to catch cases where a corrupt ELF or core file
contained an invalid length value in a Dwarf debug frame FDE header.
It was checking for buffer overflow but not cases where the length was
negative or caused pointer wrap-around.

In addition to the additional validity check, this patch cleans up the
multiple signed/unsigned conversions on the length field so that an
unsigned representation is used consistently throughout.

This patch fixes CVE-2017-9778 and PR gdb/21600.

2019-04-25  Sandra Loosemore  <sandra@codesourcery.com>
	    Kang Li <kanglictf@gmail.com>

	PR gdb/21600

	* dwarf2-frame.c (read_initial_length): Be consistent about using
	unsigned representation of length.
	(decode_frame_entry_1): Likewise.  Check for wraparound of
	end pointer as well as buffer overflow.

Upstream-Status: Backport
CVE: CVE-2017-9778
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>
---
 gdb/ChangeLog      | 10 ++++++++++
 gdb/dwarf2-frame.c | 14 +++++++-------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1c125de..d028d2b 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,13 @@
+2019-04-25  Sandra Loosemore  <sandra@codesourcery.com>
+	Kang Li <kanglictf@gmail.com>
+
+	PR gdb/21600
+
+	* dwarf2-frame.c (read_initial_length): Be consistent about using
+	unsigned representation of length.
+	(decode_frame_entry_1): Likewise.  Check for wraparound of
+	end pointer as well as buffer overflow.
+
 2019-05-11  Joel Brobecker  <brobecker@adacore.com>
 
 	* version.in: Set GDB version number to 8.3.
diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c
index 178ac44..dc5d3b3 100644
--- a/gdb/dwarf2-frame.c
+++ b/gdb/dwarf2-frame.c
@@ -1488,7 +1488,7 @@ static ULONGEST
 read_initial_length (bfd *abfd, const gdb_byte *buf,
 		     unsigned int *bytes_read_ptr)
 {
-  LONGEST result;
+  ULONGEST result;
 
   result = bfd_get_32 (abfd, buf);
   if (result == 0xffffffff)
@@ -1789,7 +1789,7 @@ decode_frame_entry_1 (struct comp_unit *unit, const gdb_byte *start,
 {
   struct gdbarch *gdbarch = get_objfile_arch (unit->objfile);
   const gdb_byte *buf, *end;
-  LONGEST length;
+  ULONGEST length;
   unsigned int bytes_read;
   int dwarf64_p;
   ULONGEST cie_id;
@@ -1800,15 +1800,15 @@ decode_frame_entry_1 (struct comp_unit *unit, const gdb_byte *start,
   buf = start;
   length = read_initial_length (unit->abfd, buf, &bytes_read);
   buf += bytes_read;
-  end = buf + length;
-
-  /* Are we still within the section?  */
-  if (end > unit->dwarf_frame_buffer + unit->dwarf_frame_size)
-    return NULL;
+  end = buf + (size_t) length;
 
   if (length == 0)
     return end;
 
+  /* Are we still within the section?  */
+  if (end <= buf || end > unit->dwarf_frame_buffer + unit->dwarf_frame_size)
+    return NULL;
+
   /* Distinguish between 32 and 64-bit encoded frame info.  */
   dwarf64_p = (bytes_read == 12);
 
-- 
2.20.1