Re: [syzbot] net-next boot error: WARNING: refcount bug in fib_create_info

On 8/3/21 3:04 PM, Jakub Kicinski wrote:

quoted

quoted

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index f29feb7772da..bb9949f6bb70 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c

@@ -1428,6 +1428,7 @@ struct fib_info *fib_create_info(struct fib_config

*cfg,
   	}

   	fib_info_cnt++;
+	refcount_set(&fi->fib_treeref, 1);
   	fi->fib_net = net;
   	fi->fib_protocol = cfg->fc_protocol;
   	fi->fib_scope = cfg->fc_scope;

Oops, it's already fixed in -next, so

#syz fix: ipv4: Fix refcount warning for new fib_info


BTW: there is one more bug with refcounts:

link_it:
	ofi = fib_find_info(fi);
	if (ofi) {
		fi->fib_dead = 1;
		free_fib_info(fi);
		refcount_inc(&ofi->fib_treeref);

		^^^^^^^^^^^^^^^^^^^^^^^
		/ *fib_treeref is 0 here */

Why 0? ofi is an existing object it's already initialized.

yes, it is an existing object with a non-0 refcount.

quoted

		return ofi;
	}

	refcount_set(&fi->fib_treeref, 1);

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index f29feb7772da..38d1fc4d0be1 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c

@@ -1543,6 +1543,8 @@ struct fib_info *fib_create_info(struct fib_config 

*cfg,
  	}

  link_it:
+	refcount_set(&fi->fib_treeref, 1);

moving the refcount_set here causes all kinds of problems with the
release and error paths in this function.