UBUNTU-CVE-2024-46828
In the Linux kernel, the following vulnerability has been resolved: sched: sch_cake: fix bulk flow accounting logic for host fairness In sch_cake, we keep track of the count of active bulk flows per host, when running in dst/src host fairness mode, which is used as the round-robin weight when iterating through flows. The count of active bulk flows is updated whenever a flow changes state. This has a peculiar interaction with the hash collision handling: when a hash collision occurs (after the set-associative hashing), the state of the hash bucket is simply updated to match the new packet that collided, and if host fairness is enabled, that also means assigning new per-host state to the flow. For this reason, the bulk flow counters of the host(s) assigned to the flow are decremented, before new state is assigned (and the counters, which may not belong to the same host anymore, are incremented again). Back when this code was introduced, the host fairness mode was always enabled, so the decrement was unconditional. When the configuration flags were introduced the *increment* was made conditional, but the *decrement* was not. Which of course can lead to a spurious decrement (and associated wrap-around to U16_MAX). AFAICT, when host fairness is disabled, the decrement and wrap-around happens as soon as a hash collision occurs (which is not that common in itself, due to the set-associative hashing). However, in most cases this is harmless, as the value is only used when host fairness mode is enabled. So in order to trigger an array overflow, sch_cake has to first be configured with host fairness disabled, and while running in this mode, a hash collision has to occur to cause the overflow. Then, the qdisc has to be reconfigured to enable host fairness, which leads to the array out-of-bounds because the wrapped-around value is retained and used as an array index. It seems that syzbot managed to trigger this, which is quite impressive in its own right. This patch fixes the issue by introducing the same conditional check on decrement as is used on increment. The original bug predates the upstreaming of cake, but the commit listed in the Fixes tag touched that code, meaning that this patch won't apply before that.
02 / AFFECTED SOFTWARE
Affected packages
17 explicit affected versions
17 explicit affected versions
51 explicit affected versions
14 explicit affected versions
8 explicit affected versions
1 explicit affected versions
1 explicit affected versions
13 explicit affected versions
6 explicit affected versions
14 explicit affected versions
10 explicit affected versions
33 explicit affected versions
1 explicit affected versions
88 explicit affected versions
7 explicit affected versions
10 explicit affected versions
11 explicit affected versions
38 explicit affected versions
52 explicit affected versions
7 explicit affected versions
18 explicit affected versions
10 explicit affected versions
26 explicit affected versions
50 explicit affected versions
12 explicit affected versions
19 explicit affected versions
6 explicit affected versions
61 explicit affected versions
47 explicit affected versions
68 explicit affected versions
57 explicit affected versions
47 explicit affected versions
8 explicit affected versions
14 explicit affected versions
54 explicit affected versions
7 explicit affected versions
53 explicit affected versions
9 explicit affected versions
95 explicit affected versions
13 explicit affected versions
11 explicit affected versions
35 explicit affected versions
14 explicit affected versions
18 explicit affected versions
18 explicit affected versions
15 explicit affected versions
64 explicit affected versions
14 explicit affected versions
97 explicit affected versions
13 explicit affected versions
4 explicit affected versions
23 explicit affected versions
18 explicit affected versions
21 explicit affected versions
16 explicit affected versions
10 explicit affected versions
52 explicit affected versions
16 explicit affected versions
7 explicit affected versions
12 explicit affected versions
45 explicit affected versions
12 explicit affected versions
14 explicit affected versions
7 explicit affected versions
85 explicit affected versions
12 explicit affected versions
14 explicit affected versions
100 explicit affected versions
108 explicit affected versions
12 explicit affected versions
9 explicit affected versions
96 explicit affected versions
9 explicit affected versions
1 explicit affected versions
10 explicit affected versions
37 explicit affected versions
13 explicit affected versions
29 explicit affected versions
35 explicit affected versions
26 explicit affected versions
13 explicit affected versions
9 explicit affected versions
100 explicit affected versions
58 explicit affected versions
8 explicit affected versions
9 explicit affected versions
83 explicit affected versions
56 explicit affected versions
33 explicit affected versions
23 explicit affected versions
10 explicit affected versions
1 explicit affected versions
98 explicit affected versions
45 explicit affected versions
39 explicit affected versions
55 explicit affected versions
10 explicit affected versions
11 explicit affected versions
12 explicit affected versions
7 explicit affected versions
12 explicit affected versions
26 explicit affected versions
16 explicit affected versions
34 explicit affected versions
1 explicit affected versions
13 explicit affected versions
16 explicit affected versions
58 explicit affected versions
16 explicit affected versions
58 explicit affected versions
46 explicit affected versions
3 explicit affected versions
1 explicit affected versions
2 explicit affected versions
65 explicit affected versions
12 explicit affected versions
44 explicit affected versions
27 explicit affected versions
30 explicit affected versions
1 explicit affected versions
19 explicit affected versions
5 explicit affected versions
8 explicit affected versions
1 explicit affected versions
10 explicit affected versions
13 explicit affected versions
13 explicit affected versions
87 explicit affected versions
13 explicit affected versions
52 explicit affected versions
7 explicit affected versions
50 explicit affected versions
10 explicit affected versions
14 explicit affected versions
13 explicit affected versions
12 explicit affected versions
87 explicit affected versions
44 explicit affected versions
16 explicit affected versions
3 explicit affected versions
8 explicit affected versions
44 explicit affected versions
37 explicit affected versions
17 explicit affected versions
14 explicit affected versions
7 explicit affected versions
38 explicit affected versions
47 explicit affected versions
9 explicit affected versions
47 explicit affected versions
11 explicit affected versions
55 explicit affected versions
7 explicit affected versions
28 explicit affected versions
59 explicit affected versions
4 explicit affected versions
53 explicit affected versions
13 explicit affected versions
43 explicit affected versions
53 explicit affected versions
10 explicit affected versions
8 explicit affected versions
12 explicit affected versions
14 explicit affected versions
88 explicit affected versions
4 explicit affected versions
77 explicit affected versions
11 explicit affected versions
1 explicit affected versions
10 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: sched: sch_cake: fix bulk flow accounting logic for host fairness In sch_cake, we keep track of the count of active bulk flows per host, when running in dst/src host fairness mode, which is used as the round-robin weight when iterating through flows. The count of active bulk flows is updated whenever a flow changes state. This has a peculiar interaction with the hash collision handling: when a hash collision occurs (after the set-associative hashing), the state of the hash bucket is simply updated to match the new packet that collided, and if host fairness is enabled, that also means assigning new per-host state to the flow. For this reason, the bulk flow counters of the host(s) assigned to the flow are decremented, before new state is assigned (and the counters, which may not belong to the same host anymore, are incremented again). Back when this code was introduced, the host fairness mode was always enabled, so the decrement was unconditional. When the configuration flags were introduced the *increment* was made conditional, but the *decrement* was not. Which of course can lead to a spurious decrement (and associated wrap-around to U16_MAX). AFAICT, when host fairness is disabled, the decrement and wrap-around happens as soon as a hash collision occurs (which is not that common in itself, due to the set-associative hashing). However, in most cases this is harmless, as the value is only used when host fairness mode is enabled. So in order to trigger an array overflow, sch_cake has to first be configured with host fairness disabled, and while running in this mode, a hash collision has to occur to cause the overflow. Then, the qdisc has to be reconfigured to enable host fairness, which leads to the array out-of-bounds because the wrapped-around value is retained and used as an array index. It seems that syzbot managed to trigger this, which is quite impressive in its own right. This patch fixes the issue by introducing the same conditional check on decrement as is used on increment. The original bug predates the upstreaming of cake, but the commit listed in the Fixes tag touched that code, meaning that this patch won't apply before that.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/546ea84d07e3e324644025e2aae2d12ea4c5896e
- https://git.kernel.org/stable/c/4a4eeefa514db570be025ab46d779af180e2c9bb
- https://git.kernel.org/stable/c/546ea84d07e3e324644025e2aae2d12ea4c5896e
- https://git.kernel.org/stable/c/549e407569e08459d16122341d332cb508024094
- https://git.kernel.org/stable/c/7725152b54d295b7da5e34c2f419539b30d017bd
- https://git.kernel.org/stable/c/cde71a5677971f4f1b69b25e854891dbe78066a4
- https://git.kernel.org/stable/c/d4a9039a7b3d8005b90c7b1a55a306444f0e5447
- https://git.kernel.org/stable/c/d7c01c0714c04431b5e18cf17a9ea68a553d1c3c
- https://ubuntu.com/security/CVE-2024-46828
- https://ubuntu.com/security/notices/USN-7088-1
- https://ubuntu.com/security/notices/USN-7088-2
- https://ubuntu.com/security/notices/USN-7088-3
- https://ubuntu.com/security/notices/USN-7088-4
- https://ubuntu.com/security/notices/USN-7088-5
- https://ubuntu.com/security/notices/USN-7100-1
- https://ubuntu.com/security/notices/USN-7100-2
- https://ubuntu.com/security/notices/USN-7119-1
- https://ubuntu.com/security/notices/USN-7123-1
- https://ubuntu.com/security/notices/USN-7144-1
- https://ubuntu.com/security/notices/USN-7154-1
- https://ubuntu.com/security/notices/USN-7154-2
- https://ubuntu.com/security/notices/USN-7155-1
- https://ubuntu.com/security/notices/USN-7156-1
- https://ubuntu.com/security/notices/USN-7194-1
- https://ubuntu.com/security/notices/USN-7196-1
- https://www.cve.org/CVERecord?id=CVE-2024-46828