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

[Coly Li]

> 2023年2月2日 23:15，Zheng Wang <zyytlz.wz@xxxxxxx> 写道：
> 
> 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@xxxxxxx>
> ---
> 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;
> 


The above change can be a single patch.

And the rested change can be another cleanup patch.

> @@ -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);

And there will be 2 patches as I suggested.

Thanks.

Coly Li