mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-08-27 23:25:13 -04:00
09c447564f
When the same BPF_LDX instruction is reached through paths that yield different pointer types, save_aux_ptr_type() merges them into a single type which is later used by bpf_convert_ctx_accesses() to decide whether the load has to be rewritten into a BPF_PROBE_MEM one. Beforef2362a57ae("bpf: allow void* cast using bpf_rdonly_cast()") the merge only accepted two PTR_TO_BTF_ID pointers and unconditionally fell back to PTR_TO_BTF_ID | PTR_UNTRUSTED, so the merged type was always one that gets the BPF_PROBE_MEM rewrite. However, the mentioned commit widened the merge to also cover a PTR_TO_MEM base and replaced the fallback by a union of the PTR_UNTRUSTED and MEM_RDONLY flags. A union of flags though cannot express the property the later rewrite is built upon, some examples: - PTR_TO_MEM merged with PTR_TO_BTF_ID | PTR_UNTRUSTED gets PTR_TO_MEM | PTR_UNTRUSTED but only the MEM_RDONLY variant is valid - PTR_TO_MEM merged with a plain PTR_TO_BTF_ID gets PTR_TO_MEM dropping the rewrite the latter type would have gotten - PTR_TO_MEM | MEM_RDONLY merged with a plain PTR_TO_BTF_ID gets PTR_TO_MEM | MEM_RDONLY which is not rewritten either since only its PTR_UNTRUSTED variant is In all three cases a program can take the unsafe path at runtime with a NULL or otherwise bad pointer and panic the kernel on the faulting load: BUG: kernel NULL pointer dereference, address: 0000000000000038 RIP: 0010:bpf_prog_77531a87032eeaf1_mixed_mem_btf_id_type+0x4b/0x65 Call Trace: <TASK> bpf_test_run+0x20b/0x460 bpf_prog_test_run_skb+0x650/0xbe0 __sys_bpf+0xb96/0x3140 __x64_sys_bpf+0x2c/0x40 do_syscall_64+0xba/0x590 Kernel panic - not syncing: Fatal exception in interrupt Note that the last two shapes have to be fixed right here, otherwise the merged type retains nothing which marks the load as fault prone, thus no rule in bpf_convert_ctx_accesses() can recover it. Fix it by normalizing the merged type instead. Reuse it in is_load_acq_unsafe() to avoid open coding, and trim the overly verbose comment which is more of an implementation detail of bpf_convert_ctx_accesses() anyway. Fixes:f2362a57ae("bpf: allow void* cast using bpf_rdonly_cast()") Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Eduard Zingerman <eddyz87@gmail.com> Link: https://lore.kernel.org/bpf/20260814215301.709827-1-daniel@iogearbox.net