CVE-2023-53136

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

af_unix: fix struct pid leaks in OOB support

syzbot reported struct pid leak [1].

Issue is that queue_oob() calls maybe_add_creds() which potentially holds a reference on a pid.

But skb->destructor is not set (either directly or by calling unix_scm_to_skb())

This means that subsequent kfree_skb() or consume_skb() would leak this reference.

In this fix, I chose to fully support scm even for the OOB message.

[1] BUG: memory leak unreferenced object 0xffff8881053e7f80 (size 128): comm syz-executor242, pid 5066, jiffies 4294946079 (age 13.220s) hex dump (first 32 bytes): 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ……………. 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ……………. backtrace: [] alloc_pid+0x6a/0x560 kernel/pid.c:180 [] copy_process+0x169f/0x26c0 kernel/fork.c:2285 [] kernel_clone+0xf7/0x610 kernel/fork.c:2684 [] __do_sys_clone+0x7c/0xb0 kernel/fork.c:2825 [] do_syscall_x64 arch/x86/entry/common.c:50 [inline] [] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 [] entry_SYSCALL_64_after_hwframe+0x63/0xcd

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/2aab4b96900272885bc157f8b236abf1cdc02e08
• https://git.kernel.org/stable/c/a59d6306263c38e5c0592ea4451ca26a0778c947
• https://git.kernel.org/stable/c/ac1968ac399205fda9ee3b18f7de7416cb3a5d0d
• https://git.kernel.org/stable/c/f3969427fb06a2c3cd6efd7faab63505cfa76e76