Re: [PATCH -next] bonding: Fix a use-after-free problem when bond_sysfs_slave_add() failed

On 02.11.21 03:55, huangguobin wrote:

I think bond_sysfs_slave_del should not be used in the error handling process, because bond_sysfs_slave_del will traverse all slave_attrs and release them. When sysfs_create_file fails, only some attributes may be created successfully.

[please don't top-post]

The suggestion was to use sysfs_create_files(), which would handle such rollback
internally. There was no mention of using bond_sysfs_slave_del().

ie. something like the following (untested):

diff --git a/drivers/net/bonding/bond_sysfs_slave.c b/drivers/net/bonding/bond_sysfs_slave.c
index fd07561da034..a1fd4bc0b0d2 100644
--- a/drivers/net/bonding/bond_sysfs_slave.c
+++ b/drivers/net/bonding/bond_sysfs_slave.c

@@ -108,15 +108,15 @@ static ssize_t ad_partner_oper_port_state_show(struct slave *slave, char *buf)
 }
 static SLAVE_ATTR_RO(ad_partner_oper_port_state);
 
-static const struct slave_attribute *slave_attrs[] = {
-       &slave_attr_state,
-       &slave_attr_mii_status,
-       &slave_attr_link_failure_count,
-       &slave_attr_perm_hwaddr,
-       &slave_attr_queue_id,
-       &slave_attr_ad_aggregator_id,
-       &slave_attr_ad_actor_oper_port_state,
-       &slave_attr_ad_partner_oper_port_state,
+static const struct attribute *slave_attrs[] = {
+       &slave_attr_state.attr,
+       &slave_attr_mii_status.attr,
+       &slave_attr_link_failure_count.attr,
+       &slave_attr_perm_hwaddr.attr,
+       &slave_attr_queue_id.attr,
+       &slave_attr_ad_aggregator_id.attr,
+       &slave_attr_ad_actor_oper_port_state.attr,
+       &slave_attr_ad_partner_oper_port_state.attr,
        NULL
 };
 

@@ -137,24 +137,16 @@ const struct sysfs_ops slave_sysfs_ops = {
 
 int bond_sysfs_slave_add(struct slave *slave)
 {
-       const struct slave_attribute **a;
        int err;
 
-       for (a = slave_attrs; *a; ++a) {
-               err = sysfs_create_file(&slave->kobj, &((*a)->attr));
-               if (err) {
-                       kobject_put(&slave->kobj);
-                       return err;
-               }
-       }
+       err = sysfs_create_files(&slave->kobj, slave_attrs);
+       if (err)
+               kobject_put(&slave->kobj);
 
-       return 0;
+       return err;
 }
 
 void bond_sysfs_slave_del(struct slave *slave)
 {
-       const struct slave_attribute **a;
-
-       for (a = slave_attrs; *a; ++a)
-               sysfs_remove_file(&slave->kobj, &((*a)->attr));
+       sysfs_remove_files(&slave->kobj, slave_attrs);
 }

-----Original Message-----
From: Julian Wiedmann [mailto:jwi@linux.ibm.com] 
Sent: Tuesday, November 2, 2021 3:31 AM
To: huangguobin <redacted>; j.vosburgh@gmail.com; vfalico@gmail.com; andy@greyhouse.net; davem@davemloft.net; kuba@kernel.org
Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next] bonding: Fix a use-after-free problem when bond_sysfs_slave_add() failed

On 01.11.21 15:34, Huang Guobin wrote:

quoted

When I do fuzz test for bonding device interface, I got the following 
use-after-free Calltrace:

[...]

quoted

Fixes: 7afcaec49696 (bonding: use kobject_put instead of _del after 
kobject_add)
Signed-off-by: Huang Guobin <redacted>
---
 drivers/net/bonding/bond_sysfs_slave.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/bonding/bond_sysfs_slave.c 

b/drivers/net/bonding/bond_sysfs_slave.c
index fd07561..d1a5b3f 100644

--- a/drivers/net/bonding/bond_sysfs_slave.c
+++ b/drivers/net/bonding/bond_sysfs_slave.c

@@ -137,18 +137,23 @@ static ssize_t slave_show(struct kobject *kobj,
 
 int bond_sysfs_slave_add(struct slave *slave)  {
-	const struct slave_attribute **a;
+	const struct slave_attribute **a, **b;
 	int err;
 
 	for (a = slave_attrs; *a; ++a) {
 		err = sysfs_create_file(&slave->kobj, &((*a)->attr));
 		if (err) {
-			kobject_put(&slave->kobj);
-			return err;
+			goto err_remove_file;
 		}
 	}
 
 	return 0;
+
+err_remove_file:
+	for (b = slave_attrs; b < a; ++b)
+		sysfs_remove_file(&slave->kobj, &((*b)->attr));
+
+	return err;
 }
 

This looks like a candidate for sysfs_create_files(), no?

quoted

 void bond_sysfs_slave_del(struct slave *slave)