[binutils-gdb] GDB: Fix out of bounds accesses with limited-length values

[binutils-gdb] GDB: Fix out of bounds accesses with limited-length values

[Maciej W. Rozycki]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=0676ec3c22f096bdf98b145b720feeef9493b5bb

commit 0676ec3c22f096bdf98b145b720feeef9493b5bb
Author: Maciej W. Rozycki <macro@embecosm.com>
Date:   Fri Feb 24 12:37:22 2023 +0000

    GDB: Fix out of bounds accesses with limited-length values
    
    Fix accesses to limited-length values in `contents_copy_raw' and
    `contents_copy_raw_bitwise' so that they observe the limit of the
    original allocation.
    
    Reported by Simon Marchi as a heap-buffer-overflow AddressSanitizer
    issue triggered with gdb.ada/limited-length.exp.
    
    Approved-By: Simon Marchi <simon.marchi@efficios.com>

Diff:
---
 gdb/value.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/gdb/value.c b/gdb/value.c
index d2c2a2d7859..9d5e694e574 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1168,6 +1168,11 @@ value::contents_copy_raw (struct value *dst, LONGEST dst_offset,
      mean we'd be copying garbage.  */
   gdb_assert (!dst->m_lazy && !m_lazy);
 
+  ULONGEST copy_length = length;
+  ULONGEST limit = m_limited_length;
+  if (limit > 0 && src_offset + length > limit)
+    copy_length = src_offset > limit ? 0 : limit - src_offset;
+
   /* The overwritten DST range gets unavailability ORed in, not
      replaced.  Make sure to remember to implement replacing if it
      turns out actually necessary.  */
@@ -1178,10 +1183,10 @@ value::contents_copy_raw (struct value *dst, LONGEST dst_offset,
   /* Copy the data.  */
   gdb::array_view<gdb_byte> dst_contents
     = dst->contents_all_raw ().slice (dst_offset * unit_size,
-					  length * unit_size);
+				      copy_length * unit_size);
   gdb::array_view<const gdb_byte> src_contents
     = contents_all_raw ().slice (src_offset * unit_size,
-				 length * unit_size);
+				 copy_length * unit_size);
   gdb::copy (src_contents, dst_contents);
 
   /* Copy the meta-data, adjusted.  */
@@ -1206,6 +1211,12 @@ value::contents_copy_raw_bitwise (struct value *dst, LONGEST dst_bit_offset,
      mean we'd be copying garbage.  */
   gdb_assert (!dst->m_lazy && !m_lazy);
 
+  ULONGEST copy_bit_length = bit_length;
+  ULONGEST bit_limit = m_limited_length * TARGET_CHAR_BIT;
+  if (bit_limit > 0 && src_bit_offset + bit_length > bit_limit)
+    copy_bit_length = (src_bit_offset > bit_limit ? 0
+		       : bit_limit - src_bit_offset);
+
   /* The overwritten DST range gets unavailability ORed in, not
      replaced.  Make sure to remember to implement replacing if it
      turns out actually necessary.  */
@@ -1220,7 +1231,7 @@ value::contents_copy_raw_bitwise (struct value *dst, LONGEST dst_bit_offset,
   gdb::array_view<const gdb_byte> src_contents = contents_all_raw ();
   copy_bitwise (dst_contents.data (), dst_bit_offset,
 		src_contents.data (), src_bit_offset,
-		bit_length,
+		copy_bit_length,
 		type_byte_order (type ()) == BFD_ENDIAN_BIG);
 
   /* Copy the meta-data.  */