[RFA] PR gdb/17210 - fix possible memory leak in read_memory_robust

[Tom Tromey]

PR gdb/17210 concerns a possible memory leak in read_memory_robust.
The bug can happen because read_memory_robust allocates memory, does
not install any cleanups, and invokes QUIT.  Similarly, it target_read
calls QUIT, so it too can potentially throw.

The fix is to install cleanups to guard the allocated memory.

Built and regtested on x86-64 Fedora 23.  I couldn't think of a way to
test this, so no new test; and of course this means it should have
more careful review.

2016-06-09  Tom Tromey  <tom@tromey.com>

	PR gdb/17210:
	* target.c (free_memory_read_result_vector): Take a pointer to the
	VEC as an argument.
	(read_memory_robust): Install a cleanup for "result".
	* mi/mi-main.c (mi_cmd_data_read_memory_bytes): Update.
---
 gdb/ChangeLog    |  8 ++++++++
 gdb/mi/mi-main.c |  2 +-
 gdb/target.c     | 15 +++++++++++----
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 9c09269..dc1c908 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2016-06-09  Tom Tromey  <tom@tromey.com>
+
+	PR gdb/17210:
+	* target.c (free_memory_read_result_vector): Take a pointer to the
+	VEC as an argument.
+	(read_memory_robust): Install a cleanup for "result".
+	* mi/mi-main.c (mi_cmd_data_read_memory_bytes): Update.
+
 2016-06-07  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* mi/mi-interp.c (mi_record_changed): Add missing braces.
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index d53bcc7..0e048f3 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -1635,7 +1635,7 @@ mi_cmd_data_read_memory_bytes (char *command, char **argv, int argc)
 
   result = read_memory_robust (current_target.beneath, addr, length);
 
-  cleanups = make_cleanup (free_memory_read_result_vector, result);
+  cleanups = make_cleanup (free_memory_read_result_vector, &result);
 
   if (VEC_length (memory_read_result_s, result) == 0)
     error (_("Unable to read memory."));
diff --git a/gdb/target.c b/gdb/target.c
index c0ce46d..442d632 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -1793,15 +1793,15 @@ read_whatever_is_readable (struct target_ops *ops,
 void
 free_memory_read_result_vector (void *x)
 {
-  VEC(memory_read_result_s) *v = (VEC(memory_read_result_s) *) x;
+  VEC(memory_read_result_s) **v = (VEC(memory_read_result_s) **) x;
   memory_read_result_s *current;
   int ix;
 
-  for (ix = 0; VEC_iterate (memory_read_result_s, v, ix, current); ++ix)
+  for (ix = 0; VEC_iterate (memory_read_result_s, *v, ix, current); ++ix)
     {
       xfree (current->data);
     }
-  VEC_free (memory_read_result_s, v);
+  VEC_free (memory_read_result_s, *v);
 }
 
 VEC(memory_read_result_s) *
@@ -1810,6 +1810,8 @@ read_memory_robust (struct target_ops *ops,
 {
   VEC(memory_read_result_s) *result = 0;
   int unit_size = gdbarch_addressable_memory_unit_size (target_gdbarch ());
+  struct cleanup *cleanup = make_cleanup (free_memory_read_result_vector,
+					  &result);
 
   LONGEST xfered_total = 0;
   while (xfered_total < len)
@@ -1836,6 +1838,7 @@ read_memory_robust (struct target_ops *ops,
 	{
 	  LONGEST to_read = min (len - xfered_total, region_len);
 	  gdb_byte *buffer = (gdb_byte *) xmalloc (to_read * unit_size);
+	  struct cleanup *inner_cleanup = make_cleanup (xfree, buffer);
 
 	  LONGEST xfered_partial =
 	      target_read (ops, TARGET_OBJECT_MEMORY, NULL,
@@ -1846,7 +1849,7 @@ read_memory_robust (struct target_ops *ops,
 	    {
 	      /* Got an error reading full chunk.  See if maybe we can read
 		 some subrange.  */
-	      xfree (buffer);
+	      do_cleanups (inner_cleanup);
 	      read_whatever_is_readable (ops, offset + xfered_total,
 					 offset + xfered_total + to_read,
 					 unit_size, &result);
@@ -1855,6 +1858,8 @@ read_memory_robust (struct target_ops *ops,
 	  else
 	    {
 	      struct memory_read_result r;
+
+	      discard_cleanups (inner_cleanup);
 	      r.data = buffer;
 	      r.begin = offset + xfered_total;
 	      r.end = r.begin + xfered_partial;
@@ -1864,6 +1869,8 @@ read_memory_robust (struct target_ops *ops,
 	  QUIT;
 	}
     }
+
+  discard_cleanups (cleanup);
   return result;
 }
 
-- 
2.5.5