Re: [PATCH v2] test-vmstate: fix bad GTree usage, use-after-free

["Richard W.M. Jones" <rjones@redhat.com>]

On Mon, Feb 27, 2023 at 07:35:05PM +0100, Eric Auger wrote:
> According to g_tree_foreach() documentation:
> "The tree may not be modified while iterating over it (you can't
> add/remove items)."

It might be worth noting that this bug only happens now because glib2
remove their custom slice allocator and switched to using system
malloc.  With glibc + MALLOC_PERTURB_, malloc will find these kinds of
bugs.  The relevant glib2 change that causes the problem is:

https://gitlab.gnome.org/GNOME/glib/-/commit/45b5a6c1e56d5b73cc5ed798ef59a5601e56c170

> A SIGSEV can be observed while running test-vmstate.

SIGSEGV

> Get rid of the node removal within the tree traversal. Also
> check the trees have the same number of nodes before the actual
> diff.
> 
> Fixes: 9a85e4b8f6 ("migration: Support gtree migration")
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1518
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> Reported-by: Richard W.M. Jones <rjones@redhat.com>

You can add:

Tested-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Richard W.M. Jones <rjones@redhat.com>

> ---
> 
> This is a respin of Marc-André's patch from Aug 2020, which can be
> found at
> https://lore.kernel.org/qemu-devel/20200827161826.1165971-1-marcandre.lureau@redhat.com/
> This fell through the cracks and now we hit a SIGSEV

SIGSEGV

> ---
>  tests/unit/test-vmstate.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/tests/unit/test-vmstate.c b/tests/unit/test-vmstate.c
> index 79357b29ca..0b7d5ecd68 100644
> --- a/tests/unit/test-vmstate.c
> +++ b/tests/unit/test-vmstate.c
> @@ -1073,7 +1073,6 @@ static gboolean diff_tree(gpointer key, gpointer value, gpointer data)
>      struct match_node_data d = {tp->tree2, key, value};
>  
>      g_tree_foreach(tp->tree2, tp->match_node, &d);
> -    g_tree_remove(tp->tree1, key);
>      return false;
>  }
>  
> @@ -1082,9 +1081,9 @@ static void compare_trees(GTree *tree1, GTree *tree2,
>  {
>      struct tree_cmp_data tp = {tree1, tree2, function};
>  
> +    assert(g_tree_nnodes(tree1) == g_tree_nnodes(tree2));
>      g_tree_foreach(tree1, diff_tree, &tp);
> -    assert(g_tree_nnodes(tree1) == 0);
> -    assert(g_tree_nnodes(tree2) == 0);
> +    g_tree_destroy(g_tree_ref(tree1));
>  }
>  
>  static void diff_domain(TestGTreeDomain *d1, TestGTreeDomain *d2)
> -- 
> 2.38.1

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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