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.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 21358ff31184a7562df66967ac5c5e1aa0e731a9..476dd19f7ce26ce74e13834542d39dc7d8fb6fcb 100644 (file)
--- 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.
+
 2019-04-24  Sergio Durigan Junior  <sergiodj@redhat.com>
 
        * aarch64-tdep.c (aarch64_gdbarch_init): Use "pulongest" to print

diff --git a/gdb/dwarf2-frame.c b/gdb/dwarf2-frame.c
index e2bf61bd3099465b7fc76ee748f88e47fda791de..b697afa5a13b79fc4e736dee689134c7bee276a1 100644 (file)
--- a/gdb/dwarf2-frame.c
+++ b/gdb/dwarf2-frame.c
@@ -1487,7 +1487,7 @@ 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)
@@ -1788,7 +1788,7 @@ 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;
@@ -1799,15 +1799,15 @@ 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);