From b87803391baa7e0bef60549d8841f12e549ad057 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Tue, 4 Aug 2026 22:19:16 +0200 Subject: bpf: Check load-acquire src ptr type before the load check_atomic_load() calls check_load_mem() before atomic_ptr_type_ok(). For a load-acquire that fetches into its own source register (dst_reg == src_reg), check_load_mem() overwrites src_reg's type with the type of the loaded value, so the subsequent atomic_ptr_type_ok() no longer sees the source pointer and fails to reject the disallowed types (ctx, pkt, flow_keys, sock). Since bpf_convert_ctx_accesses() does not rewrite atomic loads, the raw access to the underlying kernel object is left in place. The destination type is taken from the ctx access itself, so a load-acquire of the sk field of struct __sk_buff for example leaves the register typed as PTR_TO_SOCK_COMMON_OR_NULL, which type_is_sk_pointer() does not match either, while it actually holds unconverted struct sk_buff bytes. Once the NULL check has passed this is a type confusion, not just a leak of kernel data. Validate src_reg with check_reg_arg() and check the source pointer type with atomic_ptr_type_ok() before the load again, mirroring check_atomic_rmw(). Out-of-range register numbers are already rejected earlier by check_and_resolve_insns() (commit 503d21ef8eac ("bpf: Do register range validation early")), and the only exemption there, is_stack_arg_ldx(), requires BPF_LDX | BPF_MEM | BPF_DW and thus never matches a BPF_ATOMIC insn. atomic_ptr_type_ok() can therefore not dereference register state out of bounds, that is, the out-of-bounds read addressed by the Fixes commit below does not reappear (as proven also via selftest). Fixes: c03bb2fa327e ("bpf: Fix out-of-bounds read in check_atomic_load/store()") Reported-by: STAR Labs SG Signed-off-by: Daniel Borkmann Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260804201917.253491-1-daniel@iogearbox.net Signed-off-by: Kumar Kartikeya Dwivedi --- kernel/bpf/verifier.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel') diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 7439afdc851a..09588b7b08b0 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -6617,7 +6617,7 @@ static int check_atomic_load(struct bpf_verifier_env *env, { int err; - err = check_load_mem(env, insn, true, false, false, "atomic_load"); + err = check_reg_arg(env, insn->src_reg, SRC_OP); if (err) return err; @@ -6628,7 +6628,7 @@ static int check_atomic_load(struct bpf_verifier_env *env, return -EACCES; } - return 0; + return check_load_mem(env, insn, true, false, false, "atomic_load"); } static int check_atomic_store(struct bpf_verifier_env *env, -- cgit v1.2.3