[PATCH net-next 2/2] devlink: Fix list access without lock while reading region

[Parav Pandit]

While finding the devlink device during region reading,
devlink device list is accessed and devlink device is
returned without holding a lock. This could lead to user-after-free
accesses.

While at it, add lockdep assert to ensure that all future callers hold
the lock when calling devlink_get_from_attrs().

Fixes: 4e54795a27f5 ("devlink: Add support for region snapshot read command")
Signed-off-by: Parav Pandit <pa...@mellanox.com>
Acked-by: Jiri Pirko <j...@mellanox.com>
---
 net/core/devlink.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/core/devlink.c b/net/core/devlink.c
index 8a198ba..8cd773b 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -116,6 +116,8 @@ static struct devlink *devlink_get_from_attrs(struct net 
*net,
        busname = nla_data(attrs[DEVLINK_ATTR_BUS_NAME]);
        devname = nla_data(attrs[DEVLINK_ATTR_DEV_NAME]);
 
+       lockdep_assert_held(&devlink_mutex);
+
        list_for_each_entry(devlink, &devlink_list, list) {
                if (strcmp(devlink->dev->bus->name, busname) == 0 &&
                    strcmp(dev_name(devlink->dev), devname) == 0 &&
@@ -3642,13 +3644,13 @@ static int devlink_nl_cmd_region_read_dumpit(struct 
sk_buff *skb,
        if (err)
                goto out;
 
+       mutex_lock(&devlink_mutex);
        devlink = devlink_get_from_attrs(sock_net(cb->skb->sk), attrs);
        if (IS_ERR(devlink)) {
                err = -ENODEV;
-               goto out;
+               goto out_dev;
        }
 
-       mutex_lock(&devlink_mutex);
        mutex_lock(&devlink->lock);
 
        if (!attrs[DEVLINK_ATTR_REGION_NAME] ||
@@ -3723,6 +3725,7 @@ static int devlink_nl_cmd_region_read_dumpit(struct 
sk_buff *skb,
        genlmsg_cancel(skb, hdr);
 out_unlock:
        mutex_unlock(&devlink->lock);
+out_dev:
        mutex_unlock(&devlink_mutex);
 out:
        return err;
-- 
1.8.3.1