linux/lib/kobject_uevent.c, branch v5.6

kobject: Don't trigger kobject_uevent(KOBJ_REMOVE) twice.

2019-04-01T05:37:12Z

syzbot is hitting use-after-free bug in uinput module [1]. This is because kobject_uevent(KOBJ_REMOVE) is called again due to commit 0f4dafc0563c6c49 ("Kobject: auto-cleanup on final unref") after memory allocation fault injection made kobject_uevent(KOBJ_REMOVE) from device_del() from input_unregister_device() fail, while uinput_destroy_device() is expecting that kobject_uevent(KOBJ_REMOVE) is not called after device_del() from input_unregister_device() completed. That commit intended to catch cases where nobody even attempted to send "remove" uevents. But there is no guarantee that an event will ultimately be sent. We are at the point of no return as far as the rest of the kernel is concerned; there are no repeats or do-overs. Also, it is not clear whether some subsystem depends on that commit. If no subsystem depends on that commit, it will be better to remove the state_{add,remove}_uevent_sent logic. But we don't want to risk a regression (in a patch which will be backported) by trying to remove that logic. Therefore, as a first step, let's avoid the use-after-free bug by making sure that kobject_uevent(KOBJ_REMOVE) won't be triggered twice. [1] https://syzkaller.appspot.com/bug?id=8b17c134fe938bbddd75a45afaa9e68af43a362d Reported-by: syzbot Analyzed-by: Dmitry Torokhov Fixes: 0f4dafc0563c6c49 ("Kobject: auto-cleanup on final unref") Cc: Kay Sievers Signed-off-by: Tetsuo Handa Signed-off-by: Greg Kroah-Hartman

kobject: drop newline from msg string

2019-01-22T13:25:26Z

There is currently a missing terminating newline in non-switch case match when msg == NULL Signed-off-by: Bo YU Reviewed-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman

kobject: to repalce printk with pr_* style

2019-01-22T13:25:26Z

Repalce printk with pr_warn in kobject_synth_uevent and replace printk with pr_err in uevent_net_init to make both consistent with other code in kobject_uevent.c Signed-off-by: Bo YU Reviewed-by: Rafael J. Wysocki Signed-off-by: Greg Kroah-Hartman

kobject: Fix warnings in lib/kobject_uevent.c

2018-11-11T19:27:43Z

Add a blank after declaration. Signed-off-by: Bo YU Signed-off-by: Greg Kroah-Hartman

kobject: drop unnecessary cast "%llu" for u64

2018-11-11T19:27:43Z

There is no searon for u64 var cast to unsigned long long type. Signed-off-by: Bo YU Signed-off-by: Greg Kroah-Hartman

netns: restrict uevents

2018-05-01T14:22:41Z

commit 07e98962fa77 ("kobject: Send hotplug events in all network namespaces") enabled sending hotplug events into all network namespaces back in 2010. Over time the set of uevents that get sent into all network namespaces has shrunk. We have now reached the point where hotplug events for all devices that carry a namespace tag are filtered according to that namespace. Specifically, they are filtered whenever the namespace tag of the kobject does not match the namespace tag of the netlink socket. Currently, only network devices carry namespace tags (i.e. network namespace tags). Hence, uevents for network devices only show up in the network namespace such devices are created in or moved to. However, any uevent for a kobject that does not have a namespace tag associated with it will not be filtered and we will broadcast it into all network namespaces. This behavior stopped making sense when user namespaces were introduced. This patch simplifies and fixes couple of things: - Split codepath for sending uevents by kobject namespace tags: 1. Untagged kobjects - uevent_net_broadcast_untagged(): Untagged kobjects will be broadcast into all uevent sockets recorded in uevent_sock_list, i.e. into all network namespacs owned by the intial user namespace. 2. Tagged kobjects - uevent_net_broadcast_tagged(): Tagged kobjects will only be broadcast into the network namespace they were tagged with. Handling of tagged kobjects in 2. does not cause any semantic changes. This is just splitting out the filtering logic that was handled by kobj_bcast_filter() before. Handling of untagged kobjects in 1. will cause a semantic change. The reasons why this is needed and ok have been discussed in [1]. Here is a short summary: - Userspace ignores uevents from network namespaces that are not owned by the intial user namespace: Uevents are filtered by userspace in a user namespace because the received uid != 0. Instead the uid associated with the event will be 65534 == "nobody" because the global root uid is not mapped. This means we can safely and without introducing regressions modify the kernel to not send uevents into all network namespaces whose owning user namespace is not the initial user namespace because we know that userspace will ignore the message because of the uid anyway. I have a) verified that is is true for every udev implementation out there b) that this behavior has been present in all udev implementations from the very beginning. - Thundering herd: Broadcasting uevents into all network namespaces introduces significant overhead. All processes that listen to uevents running in non-initial user namespaces will end up responding to uevents that will be meaningless to them. Mainly, because non-initial user namespaces cannot easily manage devices unless they have a privileged host-process helping them out. This means that there will be a thundering herd of activity when there shouldn't be any. - Removing needless overhead/Increasing performance: Currently, the uevent socket for each network namespace is added to the global variable uevent_sock_list. The list itself needs to be protected by a mutex. So everytime a uevent is generated the mutex is taken on the list. The mutex is held *from the creation of the uevent (memory allocation, string creation etc. until all uevent sockets have been handled*. This is aggravated by the fact that for each uevent socket that has listeners the mc_list must be walked as well which means we're talking O(n^2) here. Given that a standard Linux workload usually has quite a lot of network namespaces and - in the face of containers - a lot of user namespaces this quickly becomes a performance problem (see "Thundering herd" above). By just recording uevent sockets of network namespaces that are owned by the initial user namespace we significantly increase performance in this codepath. - Injecting uevents: There's a valid argument that containers might be interested in receiving device events especially if they are delegated to them by a privileged userspace process. One prime example are SR-IOV enabled devices that are explicitly designed to be handed of to other users such as VMs or containers. This use-case can now be correctly handled since commit 692ec06d7c92 ("netns: send uevent messages"). This commit introduced the ability to send uevents from userspace. As such we can let a sufficiently privileged (CAP_SYS_ADMIN in the owning user namespace of the network namespace of the netlink socket) userspace process make a decision what uevents should be sent. This removes the need to blindly broadcast uevents into all user namespaces and provides a performant and safe solution to this problem. - Filtering logic: This patch filters by *owning user namespace of the network namespace a given task resides in* and not by user namespace of the task per se. This means if the user namespace of a given task is unshared but the network namespace is kept and is owned by the initial user namespace a listener that is opening the uevent socket in that network namespace can still listen to uevents. - Fix permission for tagged kobjects: Network devices that are created or moved into a network namespace that is owned by a non-initial user namespace currently are send with INVALID_{G,U}ID in their credentials. This means that all current udev implementations in userspace will ignore the uevent they receive for them. This has lead to weird bugs whereby new devices showing up in such network namespaces were not recognized and did not get IPs assigned etc. This patch adjusts the permission to the appropriate {g,u}id in the respective user namespace. This way udevd is able to correctly handle such devices. - Simplify filtering logic: do_one_broadcast() already ensures that only listeners in mc_list receive uevents that have the same network namespace as the uevent socket itself. So the filtering logic in kobj_bcast_filter is not needed (see [3]). This patch therefore removes kobj_bcast_filter() and replaces netlink_broadcast_filtered() with the simpler netlink_broadcast() everywhere. [1]: https://lkml.org/lkml/2018/4/4/739 [2]: https://lkml.org/lkml/2018/4/26/767 [3]: https://lkml.org/lkml/2018/4/26/738 Signed-off-by: Christian Brauner Signed-off-by: David S. Miller

uevent: add alloc_uevent_skb() helper

2018-05-01T14:22:40Z

This patch adds alloc_uevent_skb() in preparation for follow up patches. Signed-off-by: Christian Brauner Signed-off-by: David S. Miller

net: Drop pernet_operations::async

2018-03-27T17:18:09Z

Synchronous pernet_operations are not allowed anymore. All are asynchronous. So, drop the structure member. Signed-off-by: Kirill Tkhai Signed-off-by: David S. Miller

netns: send uevent messages

2018-03-22T15:16:43Z

This patch adds a receive method to NETLINK_KOBJECT_UEVENT netlink sockets to allow sending uevent messages into the network namespace the socket belongs to. Currently non-initial network namespaces are already isolated and don't receive uevents. There are a number of cases where it is beneficial for a sufficiently privileged userspace process to send a uevent into a network namespace. One such use case would be debugging and fuzzing of a piece of software which listens and reacts to uevents. By running a copy of that software inside a network namespace, specific uevents could then be presented to it. More concretely, this would allow for easy testing of udevd/ueventd. This will also allow some piece of software to run components inside a separate network namespace and then effectively filter what that software can receive. Some examples of software that do directly listen to uevents and that we have in the past attempted to run inside a network namespace are rbd (CEPH client) or the X server. Implementation: The implementation has been kept as simple as possible from the kernel's perspective. Specifically, a simple input method uevent_net_rcv() is added to NETLINK_KOBJECT_UEVENT sockets which completely reuses existing af_netlink infrastructure and does neither add an additional netlink family nor requires any user-visible changes. For example, by using netlink_rcv_skb() we can make use of existing netlink infrastructure to report back informative error messages to userspace. Furthermore, this implementation does not introduce any overhead for existing uevent generating codepaths. The struct netns got a new uevent socket member that records the uevent socket associated with that network namespace including its position in the uevent socket list. Since we record the uevent socket for each network namespace in struct net we don't have to walk the whole uevent socket list. Instead we can directly retrieve the relevant uevent socket and send the message. At exit time we can now also trivially remove the uevent socket from the uevent socket list. This keeps the codepath very performant without introducing needless overhead and even makes older codepaths faster. Uevent sequence numbers are kept global. When a uevent message is sent to another network namespace the implementation will simply increment the global uevent sequence number and append it to the received uevent. This has the advantage that the kernel will never need to parse the received uevent message to replace any existing uevent sequence numbers. Instead it is up to the userspace process to remove any existing uevent sequence numbers in case the uevent message to be sent contains any. Security: In order for a caller to send uevent messages to a target network namespace the caller must have CAP_SYS_ADMIN in the owning user namespace of the target network namespace. Additionally, any received uevent message is verified to not exceed size UEVENT_BUFFER_SIZE. This includes the space needed to append the uevent sequence number. Testing: This patch has been tested and verified to work with the following udev implementations: 1. CentOS 6 with udevd version 147 2. Debian Sid with systemd-udevd version 237 3. Android 7.1.1 with ueventd Signed-off-by: Christian Brauner Signed-off-by: David S. Miller

net: add uevent socket member

2018-03-22T15:16:42Z

This commit adds struct uevent_sock to struct net. Since struct uevent_sock records the position of the uevent socket in the uevent socket list we can trivially remove it from the uevent socket list during cleanup. This speeds up the old removal codepath. Note, list_del() will hit __list_del_entry_valid() in its call chain which will validate that the element is a member of the list. If it isn't it will take care that the list is not modified. Signed-off-by: Christian Brauner Signed-off-by: David S. Miller