Re: [PATCH] malloc: Check for large bin list corruption when inserting unsorted chunk

[Adam Maris <amaris@redhat.com>]

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On Tue, Feb 12, 2019 at 5:13 PM Adam Maris <amaris@redhat.com> wrote:
>
> Fixes bug 24216. This patch adds security checks for bk and bk_nextsize pointers
> of chunks in large bin when inserting chunk from unsorted bin. It was possible
> to write the pointer to victim (newly inserted chunk) to arbitrary memory
> locations if bk or bk_nextsize pointers of the next large bin chunk
> got corrupted.
>

Sending again with patch as attachment for better readability.

Best Regards,

Adam Mariš

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diff --git a/malloc/malloc.c b/malloc/malloc.c
index 6e766d11bc..801ba1f499 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3876,10 +3876,14 @@ _int_malloc (mstate av, size_t bytes)
                         {
                           victim->fd_nextsize = fwd;
                           victim->bk_nextsize = fwd->bk_nextsize;
+                          if (__glibc_unlikely (fwd->bk_nextsize->fd_nextsize != fwd))
+                            malloc_printerr ("malloc(): largebin double linked list corrupted (nextsize)");
                           fwd->bk_nextsize = victim;
                           victim->bk_nextsize->fd_nextsize = victim;
                         }
                       bck = fwd->bk;
+                      if (bck->fd != fwd)
+                        malloc_printerr ("malloc(): largebin double linked list corrupted (bk)");
                     }
                 }
               else