CVE-2024-58060

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

bpf: Reject struct_ops registration that uses module ptr and the module btf_id is missing

There is a UAF report in the bpf_struct_ops when CONFIG_MODULES=n. In particular, the report is on tcp_congestion_ops that has a "struct module *owner" member.

For struct_ops that has a "struct module *owner" member, it can be extended either by the regular kernel module or by the bpf_struct_ops. bpf_try_module_get() will be used to do the refcounting and different refcount is done based on the owner pointer. When CONFIG_MODULES=n, the btf_id of the "struct module" is missing:

WARN: resolve_btfids: unresolved symbol module

Thus, the bpf_try_module_get() cannot do the correct refcounting.

Not all subsystem's struct_ops requires the "struct module *owner" member. e.g. the recent sched_ext_ops.

This patch is to disable bpf_struct_ops registration if the struct_ops has the "struct module *" member and the "struct module" btf_id is missing. The btf_type_is_fwd() helper is moved to the btf.h header file for this test.

This has happened since the beginning of bpf_struct_ops which has gone through many changes. The Fixes tag is set to a recent commit that this patch can apply cleanly. Considering CONFIG_MODULES=n is not common and the age of the issue, targeting for bpf-next also.

The default Red Hat Enterprise Linux kernel prevents unprivileged users from being able to use eBPF by the kernel.unprivileged_bpf_disabled sysctl. This would require a privileged user with CAP_SYS_ADMIN or root to be able to abuse this flaw reducing its attack space.

For the Red Hat Enterprise Linux 9 to confirm the current state, inspect the sysctl with the command:

cat /proc/sys/kernel/unprivileged_bpf_disabled

The setting of 1 would mean that unprivileged users can not use eBPF, mitigating the flaw.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.