From patchwork Thu Aug 25 21:26:47 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Borkmann X-Patchwork-Id: 12955228 X-Patchwork-Delegate: bpf@iogearbox.net 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 1493BECAAA2 for ; Thu, 25 Aug 2022 21:27:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232671AbiHYV1J (ORCPT ); Thu, 25 Aug 2022 17:27:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44830 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231837AbiHYV1J (ORCPT ); Thu, 25 Aug 2022 17:27:09 -0400 Received: from www62.your-server.de (www62.your-server.de [213.133.104.62]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7011CBD2AA for ; Thu, 25 Aug 2022 14:27:07 -0700 (PDT) Received: from 226.206.1.85.dynamic.wline.res.cust.swisscom.ch ([85.1.206.226] helo=localhost) by www62.your-server.de with esmtpsa (TLSv1.3:TLS_AES_256_GCM_SHA384:256) (Exim 4.92.3) (envelope-from ) id 1oRKNU-0001Tq-1E; Thu, 25 Aug 2022 23:27:04 +0200 From: Daniel Borkmann To: ast@kernel.org Cc: andrii@kernel.org, bpf@vger.kernel.org, Daniel Borkmann , Hsin-Wei Hung , Shung-Hsi Yu Subject: [PATCH bpf] bpf: Don't use tnum_range on array range checking for poke descriptors Date: Thu, 25 Aug 2022 23:26:47 +0200 Message-Id: <984b37f9fdf7ac36831d2137415a4a915744c1b6.1661462653.git.daniel@iogearbox.net> X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.103.6/26638/Thu Aug 25 09:54:06 2022) Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net Hsin-Wei reported a KASAN splat triggered by their BPF runtime fuzzer which is based on a customized syzkaller: BUG: KASAN: slab-out-of-bounds in bpf_int_jit_compile+0x1257/0x13f0 Read of size 8 at addr ffff888004e90b58 by task syz-executor.0/1489 CPU: 1 PID: 1489 Comm: syz-executor.0 Not tainted 5.19.0 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 Call Trace: dump_stack_lvl+0x9c/0xc9 print_address_description.constprop.0+0x1f/0x1f0 ? bpf_int_jit_compile+0x1257/0x13f0 kasan_report.cold+0xeb/0x197 ? kvmalloc_node+0x170/0x200 ? bpf_int_jit_compile+0x1257/0x13f0 bpf_int_jit_compile+0x1257/0x13f0 ? arch_prepare_bpf_dispatcher+0xd0/0xd0 ? rcu_read_lock_sched_held+0x43/0x70 bpf_prog_select_runtime+0x3e8/0x640 ? bpf_obj_name_cpy+0x149/0x1b0 bpf_prog_load+0x102f/0x2220 ? __bpf_prog_put.constprop.0+0x220/0x220 ? find_held_lock+0x2c/0x110 ? __might_fault+0xd6/0x180 ? lock_downgrade+0x6e0/0x6e0 ? lock_is_held_type+0xa6/0x120 ? __might_fault+0x147/0x180 __sys_bpf+0x137b/0x6070 ? bpf_perf_link_attach+0x530/0x530 ? new_sync_read+0x600/0x600 ? __fget_files+0x255/0x450 ? lock_downgrade+0x6e0/0x6e0 ? fput+0x30/0x1a0 ? ksys_write+0x1a8/0x260 __x64_sys_bpf+0x7a/0xc0 ? syscall_enter_from_user_mode+0x21/0x70 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f917c4e2c2d The problem here is that a range of tnum_range(0, map->max_entries - 1) has limited ability to represent the concrete tight range with the tnum as the set of resulting states from value + mask can result in a superset of the actual intended range, and as such a tnum_in(range, reg->var_off) check may yield true when it shouldn't, for example tnum_range(0, 2) would result in 00XX -> v = 0000, m = 0011 such that the intended set of {0, 1, 2} is here represented by a less precise superset of {0, 1, 2, 3}. As the register is known const scalar, really just use the concrete reg->var_off.value for the upper index check. Fixes: d2e4c1e6c294 ("bpf: Constant map key tracking for prog array pokes") Reported-by: Hsin-Wei Hung Signed-off-by: Daniel Borkmann Cc: Shung-Hsi Yu Acked-by: John Fastabend --- kernel/bpf/verifier.c | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 30c6eebce146..3eadb14e090b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7033,8 +7033,7 @@ record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta, struct bpf_insn_aux_data *aux = &env->insn_aux_data[insn_idx]; struct bpf_reg_state *regs = cur_regs(env), *reg; struct bpf_map *map = meta->map_ptr; - struct tnum range; - u64 val; + u64 val, max; int err; if (func_id != BPF_FUNC_tail_call) @@ -7044,10 +7043,11 @@ record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta, return -EINVAL; } - range = tnum_range(0, map->max_entries - 1); reg = ®s[BPF_REG_3]; + val = reg->var_off.value; + max = map->max_entries; - if (!register_is_const(reg) || !tnum_in(range, reg->var_off)) { + if (!(register_is_const(reg) && val < max)) { bpf_map_key_store(aux, BPF_MAP_KEY_POISON); return 0; } @@ -7055,8 +7055,6 @@ record_func_key(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta, err = mark_chain_precision(env, BPF_REG_3); if (err) return err; - - val = reg->var_off.value; if (bpf_map_key_unseen(aux)) bpf_map_key_store(aux, val); else if (!bpf_map_key_poisoned(aux) &&