From: Yiyang Chen Date: Wed, 29 Jul 2026 15:18:28 +0000 (+0000) Subject: bpf: Preserve pointer state for commuted arithmetic X-Git-Tag: v7.2-rc7~18^2~6^2~2 X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=a4c6f804b44c5c790269b25e0e61cf4e9f117c86;p=thirdparty%2Fkernel%2Flinux.git bpf: Preserve pointer state for commuted arithmetic When scalar += pointer is handled in adjust_ptr_min_max_vals(), the destination register inherits the pointer state from the source pointer. Copying only selected fields is fragile because pointer provenance is tracked by several bpf_reg_state fields. Use the caller's temporary offset register to preserve the scalar operand while replacing the destination with the full pointer state. This preserves the frame number for PTR_TO_STACK registers and keeps parent identity fields consistent. Fixes: f4d7e40a5b71 ("bpf: introduce function calls (verification)") Signed-off-by: Yiyang Chen Tested-by: Daniel Wade Acked-by: Shung-Hsi Yu Link: https://patch.msgid.link/20260729-c3-035-public-bpf-v4-v4-2-8ee297e2346b@mails.tsinghua.edu.cn Signed-off-by: Eduard Zingerman --- diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9792d6622ffd..cdb61fab8435 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13743,11 +13743,12 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, return -EACCES; } - /* In case of 'scalar += pointer', dst_reg inherits pointer type and id. - * The id may be overwritten later if we create a new variable offset. + /* For 'scalar += pointer', dst_reg inherits the complete pointer + * register state. Individual fields may be adjusted later by pointer + * arithmetic. Callers guarantee that below does not overwrite off_reg. */ - dst_reg->type = ptr_reg->type; - dst_reg->id = ptr_reg->id; + if (dst_reg != ptr_reg) + *dst_reg = *ptr_reg; if (!check_reg_sane_offset_scalar(env, off_reg, ptr_reg->type) || !check_reg_sane_offset_ptr(env, ptr_reg, ptr_reg->type)) @@ -13790,7 +13791,7 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, } break; case BPF_SUB: - if (dst_reg == off_reg) { + if (dst_reg != ptr_reg) { /* scalar -= pointer. Creates an unknown scalar */ verbose(env, "R%d tried to subtract pointer from scalar\n", dst); @@ -14808,8 +14809,8 @@ static int adjust_reg_min_max_vals(struct bpf_verifier_env *env, err = mark_chain_precision(env, insn->dst_reg); if (err) return err; - return adjust_ptr_min_max_vals(env, insn, - src_reg, dst_reg); + off_reg = *dst_reg; + return adjust_ptr_min_max_vals(env, insn, src_reg, &off_reg); } } else if (ptr_reg) { /* pointer += scalar */