From: Cupertino Miranda Date: Wed, 4 Mar 2026 19:50:17 +0000 (+0000) Subject: bpf: detect non null pointer with register operand in JEQ/JNE. X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=2f4cb53eed448c1aeb6f4b40cf9c810716d8218c;p=thirdparty%2Flinux.git bpf: detect non null pointer with register operand in JEQ/JNE. This patch adds support to validate a pointer as not null when its value is compared to a register whose value the verifier knows to be null. Initial pattern only verifies against an immediate operand. Signed-off-by: Cupertino Miranda Cc: David Faust Cc: Jose Marchesi Cc: Elena Zannoni Acked-by: Eduard Zingerman Link: https://lore.kernel.org/r/20260304195018.181396-3-cupertino.miranda@oracle.com Signed-off-by: Alexei Starovoitov --- diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8e4f69918693e..4fbacd2149cdc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -17678,12 +17678,15 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env, } /* detect if R == 0 where R is returned from bpf_map_lookup_elem(). + * Also does the same detection for a register whose the value is + * known to be 0. * NOTE: these optimizations below are related with pointer comparison * which will never be JMP32. */ - if (!is_jmp32 && BPF_SRC(insn->code) == BPF_K && - insn->imm == 0 && (opcode == BPF_JEQ || opcode == BPF_JNE) && - type_may_be_null(dst_reg->type)) { + if (!is_jmp32 && (opcode == BPF_JEQ || opcode == BPF_JNE) && + type_may_be_null(dst_reg->type) && + ((BPF_SRC(insn->code) == BPF_K && insn->imm == 0) || + (BPF_SRC(insn->code) == BPF_X && register_is_null(src_reg)))) { /* Mark all identical registers in each branch as either * safe or unknown depending R == 0 or R != 0 conditional. */