[COMMIT] Be more careful about echo_buf arithmetic, event-stream.c.

APPROVE COMMIT

NOTE: This patch has been committed.

# HG changeset patch
# User Aidan Kehoe <[email protected]>
# Date 1426203102 0
#      Thu Mar 12 23:31:42 2015 +0000
# Node ID 6ec4964c168757948e11cb77e28966c253f00559
# Parent  27876789edc5d9485f2c9895ec4790edeaaf71f1
Be more careful about echo_buf arithmetic, event-stream.c.

src/ChangeLog addition:

2015-03-12  Aidan Kehoe  <[email protected]>

	* event-stream.c (lookup_command_event):
	Check whether echo_buf_fill_pointer is negative before using it in
	arithmetic, avoiding a crash in GC.
	Oddly the old code didn't do this check and didn't crash, but its
	echo_buf was from malloced memory, not from our string data, so
	there may have been more room to manoeuvre.

diff -r 27876789edc5 -r 6ec4964c1687 src/ChangeLog
--- a/src/ChangeLog	Thu Mar 12 00:59:27 2015 +0000
+++ b/src/ChangeLog	Thu Mar 12 23:31:42 2015 +0000
@@ -1,3 +1,12 @@
+2015-03-12  Aidan Kehoe  <[email protected]>
+
+	* event-stream.c (lookup_command_event):
+	Check whether echo_buf_fill_pointer is negative before using it in
+	arithmetic, avoiding a crash in GC.
+	Oddly the old code didn't do this check and didn't crash, but its
+	echo_buf was from malloced memory, not from our string data, so
+	there may have been more room to manoeuvre.
+
 2015-03-04  Aidan Kehoe  <[email protected]>
 
 	* sequence.c (count_with_tail):
diff -r 27876789edc5 -r 6ec4964c1687 src/event-stream.c
--- a/src/event-stream.c	Thu Mar 12 00:59:27 2015 +0000
+++ b/src/event-stream.c	Thu Mar 12 23:31:42 2015 +0000
@@ -4067,10 +4067,11 @@
 #endif
 	  {
 	    Lisp_Object prompt = Fkeymap_prompt (leaf, Qt);
-	    if (STRINGP (prompt))
+	    if (STRINGP (prompt) && STRINGP (command_builder->echo_buf))
 	      {
 		/* Append keymap prompt to key echo buffer */
-		int buf_fill_pointer = command_builder->echo_buf_fill_pointer;
+		Bytecount buf_fill_pointer
+                  = max (command_builder->echo_buf_fill_pointer, 0);
 		Bytecount len = XSTRING_LENGTH (prompt);
 
 		if (len + buf_fill_pointer + 1
@@ -4090,7 +4091,8 @@
                     /* Show the keymap prompt, but don't adjust the fill
                        pointer to reflect it. */
                     command_builder->echo_buf_end
-                      = command_builder->echo_buf_fill_pointer + len;
+                      = buf_fill_pointer + len;
+                    command_builder->echo_buf_fill_pointer = buf_fill_pointer;
 		  }
 		maybe_echo_keys (command_builder, 1);
 	      }


-- 
‘Tramadol is further fed to cattle […] when working them […] (as draft
animals) so that the animals do not get tired quickly. …’
	— Angewandte Chemie, Sept 2014, describing the social context of
	(synthetic) tramadol having been found in Cameroon tree roots.

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