CVE-2023-53272

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

net: ena: fix shift-out-of-bounds in exponential backoff

The ENA adapters on our instances occasionally reset. Once recently logged a UBSAN failure to console in the process:

UBSAN: shift-out-of-bounds in build/linux/drivers/net/ethernet/amazon/ena/ena_com.c:540:13 shift exponent 32 is too large for 32-bit type unsigned int CPU: 28 PID: 70012 Comm: kworker/u72:2 Kdump: loaded not tainted 5.15.117 Hardware name: Amazon EC2 c5d.9xlarge/, BIOS 1.0 10/16/2017 Workqueue: ena ena_fw_reset_device [ena] Call Trace: dump_stack_lvl+0x4a/0x63 dump_stack+0x10/0x16 ubsan_epilogue+0x9/0x36 __ubsan_handle_shift_out_of_bounds.cold+0x61/0x10e ? __const_udelay+0x43/0x50 ena_delay_exponential_backoff_us.cold+0x16/0x1e [ena] wait_for_reset_state+0x54/0xa0 [ena] ena_com_dev_reset+0xc8/0x110 [ena] ena_down+0x3fe/0x480 [ena] ena_destroy_device+0xeb/0xf0 [ena] ena_fw_reset_device+0x30/0x50 [ena] process_one_work+0x22b/0x3d0 worker_thread+0x4d/0x3f0 ? process_one_work+0x3d0/0x3d0 kthread+0x12a/0x150 ? set_kthread_struct+0x50/0x50 ret_from_fork+0x22/0x30

Apparently, the reset delays are getting so large they can trigger a UBSAN panic.

Looking at the code, the current timeout is capped at 5000us. Using a base value of 100us, the current code will overflow after (1«29). Even at values before 32, this function wraps around, perhaps unintentionally.

Cap the value of the exponent used for this backoff at (1«16) which is larger than currently necessary, but large enough to support bigger values in the future.

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/0939c264729d4a081ff88efce2ffdf85dc5331e0
• https://git.kernel.org/stable/c/1e760b2d18bf129b3da052c2946c02758e97d15e
• https://git.kernel.org/stable/c/1e9cb763e9bacf0c932aa948f50dcfca6f519a26
• https://git.kernel.org/stable/c/3e36cc94d6e60a27f27498adf1c71eeba769ab33
• https://git.kernel.org/stable/c/90947ebf8794e3c229fb2e16e37f1bfea6877f14