From 8bb1858b231ee90a76e21c9af2529044ac9c42e5 Mon Sep 17 00:00:00 2001
From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Thu, 11 Jul 2024 14:00:53 +0800
Subject: [PATCH] Fix $regex<n> use-after-free. Bug 2915

---
 src/exim.c      |  3 +--
 src/expand.c    |  2 +-
 src/functions.h |  2 ++
 src/globals.c   |  2 +-
 src/regex.c     | 16 ++++++++++++----
 src/smtp_in.c   |  3 +++
 6 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/src/exim.c b/src/exim.c
index fd01d13..ac6682f 100644
--- a/src/exim.c
+++ b/src/exim.c
@@ -2001,7 +2001,6 @@ regex_whitelisted_macro =
   regex_must_compile(US"^[A-Za-z0-9_/.-]*$", FALSE, TRUE);
 #endif
 
-for (i = 0; i < REGEX_VARS; i++) regex_vars[i] = NULL;
 
 /* If the program is called as "mailq" treat it as equivalent to "exim -bp";
 this seems to be a generally accepted convention, since one finds symbolic
@@ -6084,7 +6083,7 @@ MORELOOP:
   deliver_localpart_data = deliver_domain_data =
   recipient_data = sender_data = NULL;
   acl_var_m = NULL;
-  for(int i = 0; i < REGEX_VARS; i++) regex_vars[i] = NULL;
+  regex_vars_clear();
 
   store_reset(reset_point);
   }
diff --git a/src/expand.c b/src/expand.c
index 36c9f42..466733f 100644
--- a/src/expand.c
+++ b/src/expand.c
@@ -1873,7 +1873,7 @@ else if (Ustrncmp(name, "r_", 2) == 0)
   return node ? node->data.ptr : strict_acl_vars ? NULL : US"";
   }
 
-/* Handle $auth<n> variables. */
+/* Handle $auth<n>, $regex<n> variables. */
 
 if (Ustrncmp(name, "auth", 4) == 0)
   {
diff --git a/src/functions.h b/src/functions.h
index 224666c..b82edcd 100644
--- a/src/functions.h
+++ b/src/functions.h
@@ -438,6 +438,8 @@ extern int     regex(const uschar **);
 extern BOOL    regex_match(const pcre2_code *, const uschar *, int, uschar **);
 extern BOOL    regex_match_and_setup(const pcre2_code *, const uschar *, int, int);
 extern const pcre2_code *regex_must_compile(const uschar *, BOOL, BOOL);
+extern void    regex_vars_clear(void);
+
 extern void    retry_add_item(address_item *, uschar *, int);
 extern BOOL    retry_check_address(const uschar *, host_item *, uschar *, BOOL,
                  uschar **, uschar **);
diff --git a/src/globals.c b/src/globals.c
index b9dfbbb..f3d9c76 100644
--- a/src/globals.c
+++ b/src/globals.c
@@ -1319,7 +1319,7 @@ const pcre2_code *regex_EARLY_PIPE   = NULL;
 #endif
 const pcre2_code *regex_ismsgid      = NULL;
 const pcre2_code *regex_smtp_code    = NULL;
-const uschar *regex_vars[REGEX_VARS];
+const uschar *regex_vars[REGEX_VARS] = { 0 };
 #ifdef WHITELIST_D_MACROS
 const pcre2_code *regex_whitelisted_macro = NULL;
 #endif
diff --git a/src/regex.c b/src/regex.c
index 5c0f7c4..922e365 100644
--- a/src/regex.c
+++ b/src/regex.c
@@ -96,6 +96,15 @@ pcre2_match_data_free(md);
 return FAIL;
 }
 
+/* reset expansion variables */
+void
+regex_vars_clear(void)
+{
+ regex_match_string = NULL;
+ for (int i = 0; i < REGEX_VARS; i++) regex_vars[i] = NULL;
+}
+
+
 int
 regex(const uschar **listptr)
 {
@@ -103,11 +112,11 @@ unsigned long mbox_size;
 FILE *mbox_file;
 pcre_list *re_list_head;
 uschar *linebuffer;
+
 long f_pos = 0;
 int ret = FAIL;
 
-/* reset expansion variable */
-regex_match_string = NULL;
+regex_vars_clear();
 
 if (!mime_stream)				/* We are in the DATA ACL */
   {
@@ -175,8 +184,7 @@ uschar *mime_subject = NULL;
 int mime_subject_len = 0;
 int ret;
 
-/* reset expansion variable */
-regex_match_string = NULL;
+regex_vars_clear();
 
 /* precompile our regexes */
 if (!(re_list_head = compile(*listptr)))
diff --git a/src/smtp_in.c b/src/smtp_in.c
index edb0adf..34e6865 100644
--- a/src/smtp_in.c
+++ b/src/smtp_in.c
@@ -2157,7 +2157,10 @@ prdr_requested = FALSE;
 #ifdef SUPPORT_I18N
 message_smtputf8 = FALSE;
 #endif
+regex_vars_clear();
+
 body_linecount = body_zerocount = 0;
+lookup_value = NULL;                           /* Can be set by ACL */
 
 sender_rate = sender_rate_limit = sender_rate_period = NULL;
 ratelimiters_mail = NULL;           /* Updated by ratelimit ACL condition */
-- 
2.27.0