Re: [PATCH] bcache: Fix __bch_btree_node_alloc to make the failure behavior consistent

[Eric Wheeler <bcache@lists.ewheeler.net>]

On Thu, 2 Feb 2023, Zheng Wang wrote:

> In some specific situation, the return value of __bch_btree_node_alloc may
> be NULL. This may lead to poential NULL pointer dereference in caller
>  function like a calling chaion :
>  btree_split->bch_btree_node_alloc->__bch_btree_node_alloc.
> 
> Fix it by initialize return value in __bch_btree_node_alloc before return.
> 
> Fixes: cafe56359144 ("bcache: A block layer cache")
> Signed-off-by: Zheng Wang <zyytlz.wz@163.com>

Be sure to add `Cc: stable@vger.kernel.org`

-Eric

> ---
>  drivers/md/bcache/btree.c | 10 ++++++----
>  drivers/md/bcache/super.c |  2 +-
>  2 files changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 147c493a989a..35346c1d7c3c 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -1090,10 +1090,12 @@ struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op,
>  				     struct btree *parent)
>  {
>  	BKEY_PADDED(key) k;
> -	struct btree *b = ERR_PTR(-EAGAIN);
> +	struct btree *b;
>  
>  	mutex_lock(&c->bucket_lock);
>  retry:
> +	/* return ERR_PTR(-EAGAIN) when it fails */
> +	b = ERR_PTR(-EAGAIN);
>  	if (__bch_bucket_alloc_set(c, RESERVE_BTREE, &k.key, wait))
>  		goto err;
>  
> @@ -1138,7 +1140,7 @@ static struct btree *btree_node_alloc_replacement(struct btree *b,
>  {
>  	struct btree *n = bch_btree_node_alloc(b->c, op, b->level, b->parent);
>  
> -	if (!IS_ERR_OR_NULL(n)) {
> +	if (!IS_ERR(n)) {
>  		mutex_lock(&n->write_lock);
>  		bch_btree_sort_into(&b->keys, &n->keys, &b->c->sort);
>  		bkey_copy_key(&n->key, &b->key);
> @@ -1352,7 +1354,7 @@ static int btree_gc_coalesce(struct btree *b, struct btree_op *op,
>  
>  	for (i = 0; i < nodes; i++) {
>  		new_nodes[i] = btree_node_alloc_replacement(r[i].b, NULL);
> -		if (IS_ERR_OR_NULL(new_nodes[i]))
> +		if (IS_ERR(new_nodes[i]))
>  			goto out_nocoalesce;
>  	}
>  
> @@ -1669,7 +1671,7 @@ static int bch_btree_gc_root(struct btree *b, struct btree_op *op,
>  	if (should_rewrite) {
>  		n = btree_node_alloc_replacement(b, NULL);
>  
> -		if (!IS_ERR_OR_NULL(n)) {
> +		if (!IS_ERR(n)) {
>  			bch_btree_node_write_sync(n);
>  
>  			bch_btree_set_root(n);
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index ba3909bb6bea..92de714fe75e 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -2088,7 +2088,7 @@ static int run_cache_set(struct cache_set *c)
>  
>  		err = "cannot allocate new btree root";
>  		c->root = __bch_btree_node_alloc(c, NULL, 0, true, NULL);
> -		if (IS_ERR_OR_NULL(c->root))
> +		if (IS_ERR(c->root))
>  			goto err;
>  
>  		mutex_lock(&c->root->write_lock);
> -- 
> 2.25.1
> 
>