CVE-2026-98063bpf: Fix NULL-ptr-deref in btf_var_show()

Official description

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix NULL-ptr-deref in btf_var_show() btf_var_show() calls btf_type_id_resolve() unconditionally, which dereferences btf->resolved_ids. That is NULL for a base BTF - e.g. the vmlinux BTF that bpf_snprintf_btf() renders against - since base BTF is not resolved during parsing. btf_modifier_show() guards this with 'if (btf->resolved_ids)', but btf_var_show() does not. A BPF program that passes the type_id of a BTF_KIND_VAR from the vmlinux BTF to bpf_snprintf_btf() thus NULL-derefs: KASAN: probably user-memory-access in range [0x46638-0x4663f] RIP: 0010:btf_var_show (kernel/bpf/btf.c:2929) Call Trace: <TASK> btf_type_show (kernel/bpf/btf.c:8259) btf_type_snprintf_show (kernel/bpf/btf.c:8329) bpf_snprintf_btf (kernel/trace/bpf_trace.c:1047) bpf_prog_test_run_raw_tp (net/bpf/test_run.c:829) __sys_bpf (kernel/bpf/syscall.c:4804) do_syscall_64 (arch/x86/entry/syscall_64.c:84) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) </TASK> Resolve the var's type directly with btf_type_skip_modifiers() when resolved_ids is NULL, mirroring btf_modifier_show().

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/5756450c9a702da0efb4a993d0a6766b965736f3
• https://git.kernel.org/stable/c/e83fcbe3b5d4a1ffb0569bb7c280358065c6017a
• https://git.kernel.org/stable/c/e0d6a06171633d3ee3f7a39b57e5c845fb2b79f2
• https://git.kernel.org/stable/c/aec0a9c1579eb9edf534960be592d09481bd7ac3
• https://git.kernel.org/stable/c/e472ae0d97865e2021ee668a13eab64013aebf23
• https://git.kernel.org/stable/c/ca086264e98108b44fdf53971033811a48defe2b
• https://git.kernel.org/stable/c/ea383b3ea56979ce54c8aa88e6ec67164986c401
• https://git.kernel.org/stable/c/5403a383f52fc0905703b488f7c3db4b2447dc58