Summary
The Java TLS ioctl probe reads user-controlled ioctl pointers with bpf_probe_read instead of bpf_probe_read_user. An instrumented local process can therefore point OBI at kernel memory and cause that memory to be copied into telemetry.
Details
The vulnerable path is in bpf/generictracer/java_tls.c. The kprobe hooks do_vfs_ioctl, filters on fd == 0 and the Java TLS magic command, and then treats the third ioctl argument as a structured buffer. It reads fields from that pointer using bpf_probe_read, including:
- the operation byte from
arg
- connection metadata from
arg + 1
- the payload length from
arg + 1 + sizeof(connection_info_t)
If len > 0, it computes buf = arg + 1 + sizeof(connection_info_t) + sizeof(u32) and passes that pointer into handle_buf_with_connection.
The next stage, bpf/generictracer/k_tracer_defs.h, uses bpf_probe_read(args->small_buf, MIN_HTTP2_SIZE, (void *)args->u_buf); on the supplied pointer and tail-calls deeper protocol logic. The HTTP protocol path then reads from u_buf and emits the bytes through bpf_ringbuf_output in bpf/generictracer/protocol_http.h.
Because the ioctl pointer originates in user space, the probe should be using bpf_probe_read_user with strict length validation. Using bpf_probe_read instead makes it possible for an instrumented process to supply a kernel pointer and exfiltrate kernel-resident bytes into telemetry.
PoC
A complete lab reproduction requires:
- a vulnerable build of OBI with Java TLS instrumentation enabled
- a host capable of loading the BPF program
- a local process that issues the Java TLS magic ioctl with an attacker-controlled pointer
Suggested reproduction steps:
git checkout v0.0.0-rc.1+build
make build
sudo ./bin/obi
Then run a local helper that issues the matching ioctl command against fd=0 and supplies a crafted pointer.
// save as /tmp/ioctl_kernel_ptr.c
#include <stdio.h>
#include <stdint.h>
#include <sys/ioctl.h>
#include <unistd.h>
#define JAVA_TLS_MAGIC 0x0b10b1
int main(void) {
void *ptr = (void *)0xffff888000000000ULL;
long rc = ioctl(0, JAVA_TLS_MAGIC, ptr);
printf("ioctl rc=%ld\n", rc);
return 0;
}Compile and run:
cc -O2 -o /tmp/ioctl_kernel_ptr /tmp/ioctl_kernel_ptr.c
/tmp/ioctl_kernel_ptr
On a vulnerable system, if the supplied pointer references readable kernel memory and the bytes satisfy the expected Java TLS structure enough to pass the early checks, OBI can read from that address and emit the resulting bytes into telemetry. The remaining local prerequisite is a host session with sufficient BPF capability to load and inspect the probe; the compile side of the reproduction is already satisfied here.
Impact
This is a local kernel memory disclosure primitive reachable from unprivileged instrumented processes. It affects deployments that enable Java TLS support. Successful exploitation can expose kernel memory contents to the privileged OBI agent and then to downstream telemetry systems.
References
Summary
The Java TLS ioctl probe reads user-controlled ioctl pointers with
bpf_probe_readinstead ofbpf_probe_read_user. An instrumented local process can therefore point OBI at kernel memory and cause that memory to be copied into telemetry.Details
The vulnerable path is in bpf/generictracer/java_tls.c. The kprobe hooks
do_vfs_ioctl, filters onfd == 0and the Java TLS magic command, and then treats the third ioctl argument as a structured buffer. It reads fields from that pointer usingbpf_probe_read, including:argarg + 1arg + 1 + sizeof(connection_info_t)If
len > 0, it computesbuf = arg + 1 + sizeof(connection_info_t) + sizeof(u32)and passes that pointer intohandle_buf_with_connection.The next stage, bpf/generictracer/k_tracer_defs.h, uses
bpf_probe_read(args->small_buf, MIN_HTTP2_SIZE, (void *)args->u_buf);on the supplied pointer and tail-calls deeper protocol logic. The HTTP protocol path then reads fromu_bufand emits the bytes throughbpf_ringbuf_outputin bpf/generictracer/protocol_http.h.Because the ioctl pointer originates in user space, the probe should be using
bpf_probe_read_userwith strict length validation. Usingbpf_probe_readinstead makes it possible for an instrumented process to supply a kernel pointer and exfiltrate kernel-resident bytes into telemetry.PoC
A complete lab reproduction requires:
Suggested reproduction steps:
Then run a local helper that issues the matching ioctl command against
fd=0and supplies a crafted pointer.Compile and run:
On a vulnerable system, if the supplied pointer references readable kernel memory and the bytes satisfy the expected Java TLS structure enough to pass the early checks, OBI can read from that address and emit the resulting bytes into telemetry. The remaining local prerequisite is a host session with sufficient BPF capability to load and inspect the probe; the compile side of the reproduction is already satisfied here.
Impact
This is a local kernel memory disclosure primitive reachable from unprivileged instrumented processes. It affects deployments that enable Java TLS support. Successful exploitation can expose kernel memory contents to the privileged OBI agent and then to downstream telemetry systems.
References