CVE-2023-53333

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

netfilter: conntrack: dccp: copy entire header to stack buffer, not just basic one

Eric Dumazet says: nf_conntrack_dccp_packet() has an unique:

dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &_dh);

And nothing more is pulled from the packet, depending on the content. dh->dccph_doff, and/or dh->dccph_x …) So dccp_ack_seq() is happily reading stuff past the _dh buffer.

BUG: KASAN: stack-out-of-bounds in nf_conntrack_dccp_packet+0x1134/0x11c0 Read of size 4 at addr ffff000128f66e0c by task syz-executor.2/29371 [..]

Fix this by increasing the stack buffer to also include room for the extra sequence numbers and all the known dccp packet type headers, then pull again after the initial validation of the basic header.

While at it, mark packets invalid that lack 48bit sequence bit but where RFC says the type MUST use them.

Compile tested only.

v2: first skb_header_pointer() now needs to adjust the size to only pull the generic header. (Eric)

Heads-up: I intend to remove dccp conntrack support later this year.

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/26bd1f210d3783a691052c51d76bb8a8bbd24c67
• https://git.kernel.org/stable/c/337fdce450637ea663bc816edc2ba81e5cdad02e
• https://git.kernel.org/stable/c/5c618daa5038712c4a4ef8923905a2ea1b8836a1
• https://git.kernel.org/stable/c/8c0980493beed3a80d6329c44ab293dc8c032927
• https://git.kernel.org/stable/c/9bdcda7abaf22f6453e5b5efb7eb4e524095d5d8
• https://git.kernel.org/stable/c/c052797ac36813419ad3bfa54cb8615db4b41f15
• https://git.kernel.org/stable/c/ff0a3a7d52ff7282dbd183e7fc29a1fe386b0c30