CVE-2023-52828 bpf: Detect IP == ksym.end as part of BPF program
A flaw in Linux kernel BPF stack unwinding causes a kernel panic when specific BPF programs throw exceptions, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2023-52828?
CVE-2023-52828 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
bpf: Detect IP == ksym.end as part of BPF program
Now that bpf_throw kfunc is the first such call instruction that has noreturn semantics within the verifier, this also kicks in dead code elimination in unprecedented ways. For one, any instruction following a bpf_throw call will never be marked as seen. Moreover, if a callchain ends up throwing, any instructions after the call instruction to the eventually throwing subprog in callers will also never be marked as seen.
The tempting way to fix this would be to emit extra 'int3' instructions which bump the jited_len of a program, and ensure that during runtime when a program throws, we can discover its boundaries even if the call instruction to bpf_throw (or to subprogs that always throw) is emitted as the final instruction in the program.
An example of such a program would be this:
do_something(): ... r0 = 0 exit
foo(): r1 = 0 call bpf_throw r0 = 0 exit
bar(cond): if r1 != 0 goto pc+2 call do_something exit call foo r0 = 0 // Never seen by verifier exit //
main(ctx): r1 = ... call bar r0 = 0 exit
Here, if we do end up throwing, the stacktrace would be the following:
bpf_throw foo bar main
In bar, the final instruction emitted will be the call to foo, as such, the return address will be the subsequent instruction (which the JIT emits as int3 on x86). This will end up lying outside the jited_len of the program, thus, when unwinding, we will fail to discover the return address as belonging to any program and end up in a panic due to the unreliable stack unwinding of BPF programs that we never expect.
To remedy this case, make bpf_prog_ksym_find treat IP == ksym.end as part of the BPF program, so that is_bpf_text_address returns true when such a case occurs, and we are able to unwind reliably when the final instruction ends up being a call instruction.
Which versions are affected by CVE-2023-52828?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2023-52828?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2023-52828 being exploited?
There is no known exploitation of CVE-2023-52828 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2023-52828, DEBIAN-CVE-2023-52828, GHSA-6j2j-fwgf-fcf6, UBUNTU-CVE-2023-52828.