From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Fri, 24 Nov 2017 20:22:33 +0000 (+0000)
Subject: Avoid release of store if there have been later allocations.  Bug 2199
X-Git-Tag: exim-4_89_1~2
X-Git-Url: https://git.exim.org/exim.git/commitdiff_plain/4090d62a4b25782129cc1643596dc2f6e8f63bde

Avoid release of store if there have been later allocations.  Bug 2199
---

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index e937ba2c7..a2d9339c1 100644
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -59,6 +59,10 @@ JH/30 Fix a logging bug on aarch64: an unsafe routine was previously used for
       connection in response to HELO" was logged instead of the actual 4xx
       error for the HELO.
 
+JH/34 Bug 2199: fix a use-after-free while reading smtp input for header lines.
+      A crafted sequence of BDAT commands could result in in-use memory beeing
+      freed.
+
 
 Exim version 4.89
 -----------------
diff --git a/src/src/receive.c b/src/src/receive.c
index 95cf13e12..20672dbe9 100644
--- a/src/src/receive.c
+++ b/src/src/receive.c
@@ -1772,8 +1772,8 @@ for (;;)
   (and sometimes lunatic messages can have ones that are 100s of K long) we
   call store_release() for strings that have been copied - if the string is at
   the start of a block (and therefore the only thing in it, because we aren't
-  doing any other gets), the block gets freed. We can only do this because we
-  know there are no other calls to store_get() going on. */
+  doing any other gets), the block gets freed. We can only do this release if
+  there were no allocations since the once that we want to free. */
 
   if (ptr >= header_size - 4)
     {
@@ -1782,9 +1782,10 @@ for (;;)
     header_size *= 2;
     if (!store_extend(next->text, oldsize, header_size))
       {
+      BOOL release_ok = store_last_get[store_pool] == next->text;
       uschar *newtext = store_get(header_size);
       memcpy(newtext, next->text, ptr);
-      store_release(next->text);
+      if (release_ok) store_release(next->text);
       next->text = newtext;
       }
     }