bcachefs: fix possible null-ptr-deref in __bch2_ec_stripe_head_get()

The function ec_new_stripe_head_alloc() returns nullptr if kzalloc()
fails. It is crucial to verify its return value before dereferencing
it to avoid a potential nullptr dereference.

Fixes: 035d72f ("bcachefs: bch2_ec_stripe_head_get() now checks for change in rw devices")
Signed-off-by: Gaosheng Cui <[email protected]>
Signed-off-by: Kent Overstreet <[email protected]>

Author: gscui

fs/bcachefs/ec.c

@@ -1870,6 +1870,10 @@ __bch2_ec_stripe_head_get(struct btree_trans *trans,
 		}
 
 	h = ec_new_stripe_head_alloc(c, disk_label, algo, redundancy, watermark);
+	if (!h) {
+		h = ERR_PTR(-BCH_ERR_ENOMEM_stripe_head_alloc);
+		goto err;
+	}
 found:
 	if (h->rw_devs_change_count != c->rw_devs_change_count)
 		ec_stripe_head_devs_update(c, h);

fs/bcachefs/errcode.h

@@ -83,6 +83,7 @@
 	x(ENOMEM,			ENOMEM_fs_other_alloc)			\
 	x(ENOMEM,			ENOMEM_dev_alloc)			\
 	x(ENOMEM,			ENOMEM_disk_accounting)			\
+	x(ENOMEM,			ENOMEM_stripe_head_alloc)		\
 	x(ENOSPC,			ENOSPC_disk_reservation)		\
 	x(ENOSPC,			ENOSPC_bucket_alloc)			\
 	x(ENOSPC,			ENOSPC_disk_label_add)			\