From: Moritz Eckert <m.eckert@cs.ucsb.edu>
Date: Fri, 17 Aug 2018 01:08:36 +0000 (-0400)
Subject: malloc: Mitigate null-byte overflow attacks
X-Git-Tag: glibc-2.29~524
X-Git-Url: https://sourceware.org/git/?a=commitdiff_plain;h=d6db68e66dff25d12c3bc5641b60cbd7fb6ab44f;p=glibc.git

malloc: Mitigate null-byte overflow attacks

* malloc/malloc.c (_int_free): Check for corrupt prev_size vs size.
(malloc_consolidate): Likewise.
---

diff --git a/ChangeLog b/ChangeLog
index dc72e54f00..1e84f9bc1d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2018-08-16  DJ Delorie  <dj@delorie.com>
+
+	* malloc/malloc.c (_int_free): Check for corrupt prev_size vs size.
+	(malloc_consolidate): Likewise.
+
 2018-08-16  Pochang Chen  <johnchen902@gmail.com>
 
 	* malloc/malloc.c (_int_malloc.c): Verify size of top chunk.
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 9431108626..7c8bf8413c 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -4281,6 +4281,8 @@ _int_free (mstate av, mchunkptr p, int have_lock)
       prevsize = prev_size (p);
       size += prevsize;
       p = chunk_at_offset(p, -((long) prevsize));
+      if (__glibc_unlikely (chunksize(p) != prevsize))
+        malloc_printerr ("corrupted size vs. prev_size while consolidating");
       unlink(av, p, bck, fwd);
     }
 
@@ -4442,6 +4444,8 @@ static void malloc_consolidate(mstate av)
 	  prevsize = prev_size (p);
 	  size += prevsize;
 	  p = chunk_at_offset(p, -((long) prevsize));
+	  if (__glibc_unlikely (chunksize(p) != prevsize))
+	    malloc_printerr ("corrupted size vs. prev_size in fastbins");
 	  unlink(av, p, bck, fwd);
 	}