[2.28 COMMITTED] malloc: Mitigate null-byte overflow attacks

[Carlos O'Donell <carlos@redhat.com>]

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Tested on x86_64. build-many-glibcs run in progress.
--
* malloc/malloc.c (_int_free): Check for corrupt prev_size vs size.
(malloc_consolidate): Likewise.

(cherry picked from commit d6db68e66dff25d12c3bc5641b60cbd7fb6ab44f)
---
 ChangeLog       | 5 +++++
 malloc/malloc.c | 4 ++++
 2 files changed, 9 insertions(+)

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Cheers,
Carlos.

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From 7e40c3f804b5d5dbbc0519565b16101ab22fb899 Mon Sep 17 00:00:00 2001
From: Moritz Eckert <m.eckert@cs.ucsb.edu>
Date: Thu, 16 Aug 2018 21:08:36 -0400
Subject: [PATCH 3/8] malloc: Mitigate null-byte overflow attacks

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

(cherry picked from commit d6db68e66dff25d12c3bc5641b60cbd7fb6ab44f)
---
 ChangeLog       | 5 +++++
 malloc/malloc.c | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 44795b2e61..e81991066e 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);
 	}
 
-- 
2.17.2