2 files changed, 25 insertions, 8 deletions

diff --git a/src/lib/libc/stdlib/malloc.3 b/src/lib/libc/stdlib/malloc.3
index 9bd498ab50..b35b9220f6 100644
--- a/src/lib/libc/stdlib/malloc.3
+++ b/src/lib/libc/stdlib/malloc.3
@@ -30,9 +30,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"     $OpenBSD: malloc.3,v 1.129 2022/03/31 17:27:16 naddy Exp $
+.\"     $OpenBSD: malloc.3,v 1.130 2023/04/01 18:47:51 otto Exp $
 .\"
-.Dd $Mdocdate: March 31 2022 $
+.Dd $Mdocdate: April 1 2023 $
 .Dt MALLOC 3
 .Os
 .Sh NAME
@@ -293,7 +293,8 @@ order to have any effect.
 .It Cm F
 .Dq Freecheck .
 Enable more extensive double free and use after free detection.
-All chunks in the delayed free list will be checked for double frees.
+All chunks in the delayed free list will be checked for double frees and
+write after frees.
 Unused pages on the freelist are read and write protected to
 cause a segmentation fault upon access.
 .It Cm G
diff --git a/src/lib/libc/stdlib/malloc.c b/src/lib/libc/stdlib/malloc.c
index c049b2da54..2ac4b73ec0 100644
--- a/src/lib/libc/stdlib/malloc.c
+++ b/src/lib/libc/stdlib/malloc.c
@@ -1,4 +1,4 @@
-/*      $OpenBSD: malloc.c,v 1.278 2023/03/25 15:22:06 otto Exp $       */
+/*      $OpenBSD: malloc.c,v 1.279 2023/04/01 18:47:51 otto Exp $       */
 /*
  * Copyright (c) 2008, 2010, 2011, 2016 Otto Moerbeek <otto@drijf.net>
  * Copyright (c) 2012 Matthew Dempsky <matthew@openbsd.org>
@@ -1554,11 +1554,25 @@ ofree(struct dir_info **argpool, void *p, int clear, int check, size_t argsz)
                 find_chunknum(pool, info, p, mopts.chunk_canaries);
 
                 if (mopts.malloc_freecheck) {
-                        for (i = 0; i <= MALLOC_DELAYED_CHUNK_MASK; i++)
-                                if (p == pool->delayed_chunks[i])
+                        for (i = 0; i <= MALLOC_DELAYED_CHUNK_MASK; i++) {
+                                tmp = pool->delayed_chunks[i];
+                                if (tmp == p)
                                         wrterror(pool,
                                             "double free %p", p);
+                                if (tmp != NULL) {
+                                        size_t tmpsz;
+
+                                        r = find(pool, tmp);
+                                        if (r == NULL)
+                                                wrterror(pool,
+                                                    "bogus pointer ("
+                                                    "double free?) %p", tmp);
+                                        REALSIZE(tmpsz, r);
+                                        validate_junk(pool, tmp, tmpsz);
+                                }
+                        }
                 }
+
                 if (clear && argsz > 0)
                         explicit_bzero(p, argsz);
                 junk_free(pool->malloc_junk, p, sz);
@@ -1574,8 +1588,10 @@ ofree(struct dir_info **argpool, void *p, int clear, int check, size_t argsz)
                         if (r == NULL)
                                 wrterror(pool,
                                     "bogus pointer (double free?) %p", p);
-                        REALSIZE(sz, r);
-                        validate_junk(pool, p, sz);
+                        if (!mopts.malloc_freecheck) {
+                                REALSIZE(sz, r);
+                                validate_junk(pool, p, sz);
+                        }
                         free_bytes(pool, r, p);
                 }
         }