From patchwork Fri Jan 14 08:16:18 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 532249 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 729F7C4332F for ; Fri, 14 Jan 2022 08:24:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237787AbiANIYc (ORCPT ); Fri, 14 Jan 2022 03:24:32 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:32992 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240185AbiANIWc (ORCPT ); Fri, 14 Jan 2022 03:22:32 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CE96361E04; Fri, 14 Jan 2022 08:22:31 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8ADEEC36AE9; Fri, 14 Jan 2022 08:22:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1642148551; bh=EkXLKmKi0lwhKvER05e2eCfe4gmq+a56A0vUlD9i5iM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lpZhsPUVMVLMqKIx7HzcYQq9tqdOPbHTHVFi0wOCjp/qM/NVoYOYuUP0p5bRNW723 vY98a4jwHh/DBb9x+sSJ0SI+vdnp6jN8WjPGVcNXl6nYrhtFbmDCXN5P1DSph0wIx1 ojg8Ldox5F9g540WpHMTG3bWdAWlEPUy4FLM4dqw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Daniel Borkmann Subject: [PATCH 5.16 04/37] bpf: Fix out of bounds access from invalid *_or_null type verification Date: Fri, 14 Jan 2022 09:16:18 +0100 Message-Id: <20220114081545.000018750@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220114081544.849748488@linuxfoundation.org> References: <20220114081544.849748488@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Daniel Borkmann [ no upstream commit given implicitly fixed through the larger refactoring in c25b2ae136039ffa820c26138ed4a5e5f3ab3841 ] While auditing some other code, I noticed missing checks inside the pointer arithmetic simulation, more specifically, adjust_ptr_min_max_vals(). Several *_OR_NULL types are not rejected whereas they are _required_ to be rejected given the expectation is that they get promoted into a 'real' pointer type for the success case, that is, after an explicit != NULL check. One case which stands out and is accessible from unprivileged (iff enabled given disabled by default) is BPF ring buffer. From crafting a PoC, the NULL check can be bypassed through an offset, and its id marking will then lead to promotion of mem_or_null to a mem type. bpf_ringbuf_reserve() helper can trigger this case through passing of reserved flags, for example. func#0 @0 0: R1=ctx(id=0,off=0,imm=0) R10=fp0 0: (7a) *(u64 *)(r10 -8) = 0 1: R1=ctx(id=0,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm 1: (18) r1 = 0x0 3: R1_w=map_ptr(id=0,off=0,ks=0,vs=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm 3: (b7) r2 = 8 4: R1_w=map_ptr(id=0,off=0,ks=0,vs=0,imm=0) R2_w=invP8 R10=fp0 fp-8_w=mmmmmmmm 4: (b7) r3 = 0 5: R1_w=map_ptr(id=0,off=0,ks=0,vs=0,imm=0) R2_w=invP8 R3_w=invP0 R10=fp0 fp-8_w=mmmmmmmm 5: (85) call bpf_ringbuf_reserve#131 6: R0_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 6: (bf) r6 = r0 7: R0_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R6_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 7: (07) r0 += 1 8: R0_w=mem_or_null(id=2,ref_obj_id=2,off=1,imm=0) R6_w=mem_or_null(id=2,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 8: (15) if r0 == 0x0 goto pc+4 R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 9: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 9: (62) *(u32 *)(r6 +0) = 0 R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 10: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 10: (bf) r1 = r6 11: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R1_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 11: (b7) r2 = 0 12: R0_w=mem(id=0,ref_obj_id=0,off=0,imm=0) R1_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R2_w=invP0 R6_w=mem(id=0,ref_obj_id=2,off=0,imm=0) R10=fp0 fp-8_w=mmmmmmmm refs=2 12: (85) call bpf_ringbuf_submit#132 13: R6=invP(id=0) R10=fp0 fp-8=mmmmmmmm 13: (b7) r0 = 0 14: R0_w=invP0 R6=invP(id=0) R10=fp0 fp-8=mmmmmmmm 14: (95) exit from 8 to 13: safe processed 15 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 0 OK All three commits, that is b121b341e598 ("bpf: Add PTR_TO_BTF_ID_OR_NULL support"), 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it"), and the afbf21dce668 ("bpf: Support readonly/readwrite buffers in verifier") suffer the same cause and their *_OR_NULL type pendants must be rejected in adjust_ptr_min_max_vals(). Make the test more robust by reusing reg_type_may_be_null() helper such that we catch all *_OR_NULL types we have today and in future. Note that pointer arithmetic on PTR_TO_BTF_ID, PTR_TO_RDONLY_BUF, and PTR_TO_RDWR_BUF is generally allowed. Fixes: b121b341e598 ("bpf: Add PTR_TO_BTF_ID_OR_NULL support") Fixes: 457f44363a88 ("bpf: Implement BPF ring buffer and verifier support for it") Fixes: afbf21dce668 ("bpf: Support readonly/readwrite buffers in verifier") Signed-off-by: Daniel Borkmann Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7229,16 +7229,16 @@ static int adjust_ptr_min_max_vals(struc fallthrough; case PTR_TO_PACKET_END: case PTR_TO_SOCKET: - case PTR_TO_SOCKET_OR_NULL: case PTR_TO_SOCK_COMMON: - case PTR_TO_SOCK_COMMON_OR_NULL: case PTR_TO_TCP_SOCK: - case PTR_TO_TCP_SOCK_OR_NULL: case PTR_TO_XDP_SOCK: +reject: verbose(env, "R%d pointer arithmetic on %s prohibited\n", dst, reg_type_str[ptr_reg->type]); return -EACCES; default: + if (reg_type_may_be_null(ptr_reg->type)) + goto reject; break; }