CVE-2024-26665

In the Linux kernel, the following vulnerability has been resolved:

tunnels: fix out of bounds access when building IPv6 PMTU error

If the ICMPv6 error is built from a non-linear skb we get the following splat,

BUG: KASAN: slab-out-of-bounds in do_csum+0x220/0x240 Read of size 4 at addr ffff88811d402c80 by task netperf/820 CPU: 0 PID: 820 Comm: netperf Not tainted 6.8.0-rc1+ #543 … kasan_report+0xd8/0x110 do_csum+0x220/0x240 csum_partial+0xc/0x20 skb_tunnel_check_pmtu+0xeb9/0x3280 vxlan_xmit_one+0x14c2/0x4080 vxlan_xmit+0xf61/0x5c00 dev_hard_start_xmit+0xfb/0x510 __dev_queue_xmit+0x7cd/0x32a0 br_dev_queue_push_xmit+0x39d/0x6a0

Use skb_checksum instead of csum_partial who cannot deal with non-linear SKBs.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/510c869ffa4068c5f19ff4df51d1e2f3a30aaac1
• https://git.kernel.org/stable/c/7dc9feb8b1705cf00de20563b6bc4831f4c99dab
• https://git.kernel.org/stable/c/d75abeec401f8c86b470e7028a13fcdc87e5dd06
• https://git.kernel.org/stable/c/d964dd1bc1452594b4207d9229c157d9386e5d8a
• https://git.kernel.org/stable/c/e37cde7a5716466ff2a76f7f27f0a29b05b9a732
• https://git.kernel.org/stable/c/e77bf828f1ca1c47fcff58bdc26b60a9d3dfbe1d
• https://git.kernel.org/stable/c/510c869ffa4068c5f19ff4df51d1e2f3a30aaac1
• https://git.kernel.org/stable/c/7dc9feb8b1705cf00de20563b6bc4831f4c99dab
• https://git.kernel.org/stable/c/d75abeec401f8c86b470e7028a13fcdc87e5dd06
• https://git.kernel.org/stable/c/d964dd1bc1452594b4207d9229c157d9386e5d8a
• https://git.kernel.org/stable/c/e37cde7a5716466ff2a76f7f27f0a29b05b9a732
• https://git.kernel.org/stable/c/e77bf828f1ca1c47fcff58bdc26b60a9d3dfbe1d
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html