john-dev - rules.c patch for ASan fault

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Date: Thu, 3 Dec 2015 19:14:46 +0100
From: magnum <john.magnum@...hmail.com>
To: john-dev@...ts.openwall.com
Subject: rules.c patch for ASan fault

Solar,

Here's a (maybe) proposed patch against john proper:

diff --git a/src/rules.c b/src/rules.c
index 35cfe15..7eae64e 100644
--- a/src/rules.c
+++ b/src/rules.c
@@ -825,7 +825,7 @@ char *rules_apply(char *word, char *rule, int split, 
char *last)
                                 POSITION(mpos)
                                 POSITION(count)
                                 POSITION(ipos)
-                               mleft = (int)(rules_vars['m'] + 1) - mpos;
+                               mleft = (int)(rules_vars['l']) - mpos;
                                 if (count > mleft)
                                         count = mleft;
                                 if (count <= 0)

This is within the 'X' command. The rationale is that rules_vars['m'] is 
an unsigned char, initially set to (length - 1). When length is 0, 
rules_vars['m'] is thus 255. This leads to an ASan fault (at least a 
"read" fault) unless this patch is applied. There doesn't seem to be any 
more instance of similar problem.

Is there some intended behavior that this patch would break? I can't 
imagine any.

For background, see 
https://github.com/magnumripper/JohnTheRipper/issues/1744

magnum

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