UBUNTU-CVE-2024-26837
In the Linux kernel, the following vulnerability has been resolved: net: bridge: switchdev: Skip MDB replays of deferred events on offload Before this change, generation of the list of MDB events to replay would race against the creation of new group memberships, either from the IGMP/MLD snooping logic or from user configuration. While new memberships are immediately visible to walkers of br->mdb_list, the notification of their existence to switchdev event subscribers is deferred until a later point in time. So if a replay list was generated during a time that overlapped with such a window, it would also contain a replay of the not-yet-delivered event. The driver would thus receive two copies of what the bridge internally considered to be one single event. On destruction of the bridge, only a single membership deletion event was therefore sent. As a consequence of this, drivers which reference count memberships (at least DSA), would be left with orphan groups in their hardware database when the bridge was destroyed. This is only an issue when replaying additions. While deletion events may still be pending on the deferred queue, they will already have been removed from br->mdb_list, so no duplicates can be generated in that scenario. To a user this meant that old group memberships, from a bridge in which a port was previously attached, could be reanimated (in hardware) when the port joined a new bridge, without the new bridge's knowledge. For example, on an mv88e6xxx system, create a snooping bridge and immediately add a port to it: root@infix-06-0b-00:~$ ip link add dev br0 up type bridge mcast_snooping 1 && \ > ip link set dev x3 up master br0 And then destroy the bridge: root@infix-06-0b-00:~$ ip link del dev br0 root@infix-06-0b-00:~$ mvls atu ADDRESS FID STATE Q F 0 1 2 3 4 5 6 7 8 9 a DEV:0 Marvell 88E6393X 33:33:00:00:00:6a 1 static - - 0 . . . . . . . . . . 33:33:ff:87:e4:3f 1 static - - 0 . . . . . . . . . . ff:ff:ff:ff:ff:ff 1 static - - 0 1 2 3 4 5 6 7 8 9 a root@infix-06-0b-00:~$ The two IPv6 groups remain in the hardware database because the port (x3) is notified of the host's membership twice: once via the original event and once via a replay. Since only a single delete notification is sent, the count remains at 1 when the bridge is destroyed. Then add the same port (or another port belonging to the same hardware domain) to a new bridge, this time with snooping disabled: root@infix-06-0b-00:~$ ip link add dev br1 up type bridge mcast_snooping 0 && \ > ip link set dev x3 up master br1 All multicast, including the two IPv6 groups from br0, should now be flooded, according to the policy of br1. But instead the old memberships are still active in the hardware database, causing the switch to only forward traffic to those groups towards the CPU (port 0). Eliminate the race in two steps: 1. Grab the write-side lock of the MDB while generating the replay list. This prevents new memberships from showing up while we are generating the replay list. But it leaves the scenario in which a deferred event was already generated, but not delivered, before we grabbed the lock. Therefore: 2. Make sure that no deferred version of a replay event is already enqueued to the switchdev deferred queue, before adding it to the replay list, when replaying additions.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
35 explicit affected versions
43 explicit affected versions
61 explicit affected versions
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6 explicit affected versions
12 explicit affected versions
19 explicit affected versions
6 explicit affected versions
71 explicit affected versions
56 explicit affected versions
64 explicit affected versions
57 explicit affected versions
10 explicit affected versions
63 explicit affected versions
7 explicit affected versions
62 explicit affected versions
13 explicit affected versions
18 explicit affected versions
22 explicit affected versions
45 explicit affected versions
13 explicit affected versions
4 explicit affected versions
23 explicit affected versions
21 explicit affected versions
23 explicit affected versions
21 explicit affected versions
9 explicit affected versions
16 explicit affected versions
65 explicit affected versions
10 explicit affected versions
7 explicit affected versions
12 explicit affected versions
54 explicit affected versions
12 explicit affected versions
14 explicit affected versions
1 explicit affected versions
7 explicit affected versions
12 explicit affected versions
12 explicit affected versions
17 explicit affected versions
37 explicit affected versions
13 explicit affected versions
10 explicit affected versions
38 explicit affected versions
26 explicit affected versions
13 explicit affected versions
13 explicit affected versions
29 explicit affected versions
13 explicit affected versions
68 explicit affected versions
63 explicit affected versions
26 explicit affected versions
33 explicit affected versions
23 explicit affected versions
10 explicit affected versions
11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
54 explicit affected versions
48 explicit affected versions
64 explicit affected versions
10 explicit affected versions
26 explicit affected versions
1 explicit affected versions
13 explicit affected versions
16 explicit affected versions
53 explicit affected versions
3 explicit affected versions
2 explicit affected versions
51 explicit affected versions
2 explicit affected versions
12 explicit affected versions
51 explicit affected versions
27 explicit affected versions
38 explicit affected versions
8 explicit affected versions
28 explicit affected versions
5 explicit affected versions
8 explicit affected versions
10 explicit affected versions
13 explicit affected versions
13 explicit affected versions
7 explicit affected versions
55 explicit affected versions
10 explicit affected versions
12 explicit affected versions
15 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
13 explicit affected versions
26 explicit affected versions
45 explicit affected versions
37 explicit affected versions
14 explicit affected versions
38 explicit affected versions
10 explicit affected versions
54 explicit affected versions
9 explicit affected versions
53 explicit affected versions
11 explicit affected versions
64 explicit affected versions
8 explicit affected versions
7 explicit affected versions
33 explicit affected versions
4 explicit affected versions
1 explicit affected versions
1 explicit affected versions
62 explicit affected versions
13 explicit affected versions
43 explicit affected versions
8 explicit affected versions
14 explicit affected versions
4 explicit affected versions
11 explicit affected versions
1 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: net: bridge: switchdev: Skip MDB replays of deferred events on offload Before this change, generation of the list of MDB events to replay would race against the creation of new group memberships, either from the IGMP/MLD snooping logic or from user configuration. While new memberships are immediately visible to walkers of br->mdb_list, the notification of their existence to switchdev event subscribers is deferred until a later point in time. So if a replay list was generated during a time that overlapped with such a window, it would also contain a replay of the not-yet-delivered event. The driver would thus receive two copies of what the bridge internally considered to be one single event. On destruction of the bridge, only a single membership deletion event was therefore sent. As a consequence of this, drivers which reference count memberships (at least DSA), would be left with orphan groups in their hardware database when the bridge was destroyed. This is only an issue when replaying additions. While deletion events may still be pending on the deferred queue, they will already have been removed from br->mdb_list, so no duplicates can be generated in that scenario. To a user this meant that old group memberships, from a bridge in which a port was previously attached, could be reanimated (in hardware) when the port joined a new bridge, without the new bridge's knowledge. For example, on an mv88e6xxx system, create a snooping bridge and immediately add a port to it: root@infix-06-0b-00:~$ ip link add dev br0 up type bridge mcast_snooping 1 && \ > ip link set dev x3 up master br0 And then destroy the bridge: root@infix-06-0b-00:~$ ip link del dev br0 root@infix-06-0b-00:~$ mvls atu ADDRESS FID STATE Q F 0 1 2 3 4 5 6 7 8 9 a DEV:0 Marvell 88E6393X 33:33:00:00:00:6a 1 static - - 0 . . . . . . . . . . 33:33:ff:87:e4:3f 1 static - - 0 . . . . . . . . . . ff:ff:ff:ff:ff:ff 1 static - - 0 1 2 3 4 5 6 7 8 9 a root@infix-06-0b-00:~$ The two IPv6 groups remain in the hardware database because the port (x3) is notified of the host's membership twice: once via the original event and once via a replay. Since only a single delete notification is sent, the count remains at 1 when the bridge is destroyed. Then add the same port (or another port belonging to the same hardware domain) to a new bridge, this time with snooping disabled: root@infix-06-0b-00:~$ ip link add dev br1 up type bridge mcast_snooping 0 && \ > ip link set dev x3 up master br1 All multicast, including the two IPv6 groups from br0, should now be flooded, according to the policy of br1. But instead the old memberships are still active in the hardware database, causing the switch to only forward traffic to those groups towards the CPU (port 0). Eliminate the race in two steps: 1. Grab the write-side lock of the MDB while generating the replay list. This prevents new memberships from showing up while we are generating the replay list. But it leaves the scenario in which a deferred event was already generated, but not delivered, before we grabbed the lock. Therefore: 2. Make sure that no deferred version of a replay event is already enqueued to the switchdev deferred queue, before adding it to the replay list, when replaying additions.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/dc489f86257cab5056e747344f17a164f63bff4b
- https://git.kernel.org/stable/c/2d5b4b3376fa146a23917b8577064906d643925f
- https://git.kernel.org/stable/c/603be95437e7fd85ba694e75918067fb9e7754db
- https://git.kernel.org/stable/c/dc489f86257cab5056e747344f17a164f63bff4b
- https://git.kernel.org/stable/c/e0b4c5b1d760008f1dd18c07c35af0442e54f9c8
- https://ubuntu.com/security/CVE-2024-26837
- https://ubuntu.com/security/notices/USN-7455-1
- https://ubuntu.com/security/notices/USN-7455-2
- https://ubuntu.com/security/notices/USN-7455-3
- https://ubuntu.com/security/notices/USN-7455-4
- https://ubuntu.com/security/notices/USN-7455-5
- https://ubuntu.com/security/notices/USN-7459-1
- https://ubuntu.com/security/notices/USN-7459-2
- https://ubuntu.com/security/notices/USN-7460-1
- https://ubuntu.com/security/notices/USN-7475-1
- https://www.cve.org/CVERecord?id=CVE-2024-26837