From acbbc667fa218b27105e9e8d929fbed95535679f Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Fri, 4 Nov 2022 00:39:53 +0530 Subject: [PATCH] bpf: Fix slot type check in check_stack_write_var_off [ Upstream commit f5e477a861e4a20d8a1c5f7a245f3a3c3c376b03 ] For the case where allow_ptr_leaks is false, code is checking whether slot type is STACK_INVALID and STACK_SPILL and rejecting other cases. This is a consequence of incorrectly checking for register type instead of the slot type (NOT_INIT and SCALAR_VALUE respectively). Fix the check. Fixes: 01f810ace9ed ("bpf: Allow variable-offset stack access") Signed-off-by: Kumar Kartikeya Dwivedi Link: https://lore.kernel.org/r/20221103191013.1236066-5-memxor@gmail.com Signed-off-by: Alexei Starovoitov Signed-off-by: Sasha Levin --- kernel/bpf/verifier.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index cceb29b0585f09..027ead3d06800b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2772,14 +2772,17 @@ static int check_stack_write_var_off(struct bpf_verifier_env *env, spi = slot / BPF_REG_SIZE; stype = &state->stack[spi].slot_type[slot % BPF_REG_SIZE]; - if (!env->allow_ptr_leaks - && *stype != NOT_INIT - && *stype != SCALAR_VALUE) { - /* Reject the write if there's are spilled pointers in - * range. If we didn't reject here, the ptr status - * would be erased below (even though not all slots are - * actually overwritten), possibly opening the door to - * leaks. + if (!env->allow_ptr_leaks && *stype != STACK_MISC && *stype != STACK_ZERO) { + /* Reject the write if range we may write to has not + * been initialized beforehand. If we didn't reject + * here, the ptr status would be erased below (even + * though not all slots are actually overwritten), + * possibly opening the door to leaks. + * + * We do however catch STACK_INVALID case below, and + * only allow reading possibly uninitialized memory + * later for CAP_PERFMON, as the write may not happen to + * that slot. */ verbose(env, "spilled ptr in range of var-offset stack write; insn %d, ptr off: %d", insn_idx, i);