From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wr1-f41.google.com (mail-wr1-f41.google.com [209.85.221.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E643439D6D1 for ; Thu, 16 Apr 2026 11:58:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.221.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776340705; cv=none; b=rV3eGx6LYoWxVjPzFrPpoh/zf+BdSxWMHfyBUAH9dxumc1ni0ADtAZrTvsglqPz1qV8UenERRJIEDGPEYF9B9Wtp/ZbO80gy5npwCfOhZoyBCkmwbONO2H0hAj2XMW7GPgC8YyIY4gL5RA/g+9decJv4EhZFmkO5mUyLniHQUWA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776340705; c=relaxed/simple; bh=9QpOVqk9PefAIVLsbFNfDAp88LZKMe4ZC7ob89smceU=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=Du6DUVXQZSluO1sazQG/uf0mnMiQpQ0kGVRznRygvsi33VlqO0etKJCu/7+HmxchKKTxIFn0ryo3FZVr9p8M/XlqeI4nuJYh66TLe2B31qomfoMhX/rxATxv88v854nBx2Kku7zaBs1Ae/zLIZrN7G9HzGu8mRp7k7otV0aQE7E= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=gWk0m1yb; arc=none smtp.client-ip=209.85.221.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="gWk0m1yb" Received: by mail-wr1-f41.google.com with SMTP id ffacd0b85a97d-43d7605ec91so4034254f8f.3 for ; Thu, 16 Apr 2026 04:58:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1776340702; x=1776945502; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:references :in-reply-to:subject:cc:to:from:from:to:cc:subject:date:message-id :reply-to; bh=L9ylrYIuDgodTTNkfq8YPCdUP+i3S2INv5wmyzL6RM4=; b=gWk0m1ybJyP65MLbaz52n/FiTXzJv7+52/vE6sGB5Dl2GUYZfGbkuCZF/Fn3LkMugt UdXA0UhIbi1ESHOcDgGIixdOcnRMx+ofx+zNTPv+815G8wJC9zWDlNs6rRPnlEDpX9zd M3cU5KAhMG3xRnPn/gpaFUY48O/TM7kDbbL2Lx/d662P52FpXy9XQEjkYAQrxldlDCGG BwpI6sHkfpOJED+QOUUystV2Tz4TtR4p5sQcWHW3WGls1OmzdHt47cRqdZEekzkDnBIk yf2hkz17zomKz+qKaP8Lt+F6+RjlUhDt6POwTG3Es5dD4526cevff6PAxx7/12zVsVxr zSYA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776340702; x=1776945502; h=content-transfer-encoding:mime-version:message-id:date:references :in-reply-to:subject:cc:to:from:x-gm-gg:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=L9ylrYIuDgodTTNkfq8YPCdUP+i3S2INv5wmyzL6RM4=; b=VJKuqvzQf7Q4ESK27cLjRN2telBgf4flLZlsjtxMxMPWb2Ze9Z052WCjf5186wHg4x fLICFqbwxP5dNnwUetASMmfcEfYlJsifLOFUWoFFofVfwNiz5LQlfPwzxEP8JedTdxov 7fqv4reK3pSlC/eiK+9Gj6kZrSg1ihpW2NUdi+LZsxewoOe1KE10+KlpXfLn00BC5UhH KSHHtT3qsaWYnv3orj14cqlcX+38zYvU/aXIG7Vf/mqBL25TkWq4SCzSLHvSwEKk1hZj nGchocEbNfSMMVvV4Wp8w2FRwFQuw40AjFFVuN9nZ9xv3MOHWD4FvKCKWZYqJhqCB9X3 hjHw== X-Gm-Message-State: AOJu0Yx07A6nxSsFGA3hUU04J7GFnocyMUSTGck3H+2OhK1cE+ItsScg f6wqZpoFaxwfBAv4PdFr10HBf1KdP9VehhhrYEXX6Dv0usszXMDArtto X-Gm-Gg: AeBDiet87wW1tAdS42CnTsEx8T1oxCtmq2yFxOI4b4EzKdS3f/5NWxtbcLSy4WxneV7 dj7lBo5zz4FhIGr6QLVnsDnNgmkK1kd4wBVOQ73YA2WYYZjgroXbRrGod8bzs561lKgyNH55RUi 4tumed/8+sC8xmG9SxefS+ECObDtdZFxDz59X3KVxmXocNfXPa9KznZTKFgRp2eDfNCR7yJTFAr NhgFqCj8MnPgH53nCHptF9TO/lqIvlSijl8M+iiMlxCqEnegaN3duLGKFjOsb6FUG3IgFursQM1 VJyqlj2w2s0ExxYVGnwrHwU+awyhpqCHGzkcQx81GsbPTJkOIuoAgPxFMemCXedJ1pxSEHRqJn/ 7mYG7q2zSv8qLG9//iMhPDerDboUfgemKU6SeoO6+4Oe0IhbsohanRj744MEwELhM8H5ws2hJ/G EcB8eo8FyQ34v5YzA= X-Received: by 2002:a05:6000:1a8d:b0:43c:fde6:212d with SMTP id ffacd0b85a97d-43d642cd3ddmr39199178f8f.33.1776340702075; Thu, 16 Apr 2026 04:58:22 -0700 (PDT) Received: from localhost ([2620:10d:c092:500::4:7fe8]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43ead3e89ddsm12664005f8f.30.2026.04.16.04.58.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 16 Apr 2026 04:58:21 -0700 (PDT) From: Mykyta Yatsenko To: Hiker Cl , bpf@vger.kernel.org Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: NULL pointer dereference in map_kptr_match_type when storing scalar values into kptr slots In-Reply-To: References: Date: Thu, 16 Apr 2026 12:58:20 +0100 Message-ID: <87340v9kwz.fsf@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hiker Cl writes: > Hi BPF maintainers, > > I'm reporting a bug I encountered in the BPF subsystem on Linux kernel > version 7.0.0-g1f5ffc672165. > > ### Summary > A NULL pointer dereference vulnerability was discovered in the eBPF > verifier. A local user can trigger this by loading a BPF program that > attempts to store a scalar value (non-pointer) into a map slot > designated as a kptr (kernel pointer). This leads to an immediate > kernel crash (DoS). > ### Environment > - Kernel version: 7.0.0-rc6 (Commit: 71b500afd2f7 from bpf-next tree), > 7.0.0-g1f5ffc672165 (Commit: 1f5ffc672165 from linux tree) > - Architecture: x86_64 > - Config: BPF_SYSCALL=3Dy, DEBUG_INFO_BTF=3Dy > > ### Steps to Reproduce =EF=BC=88poc.c) > #include "vmlinux.h" > #include > /* BTF type tags for kptrs */ > #ifndef __kptr_untrusted > #define __kptr_untrusted __attribute__((btf_type_tag("kptr_untrusted"))) > #endif > struct map_value { > struct task_struct __kptr_untrusted *ptr; > }; > struct { > __uint(type, BPF_MAP_TYPE_LRU_HASH); > __uint(max_entries, 1); > __type(key, int); > __type(value, struct map_value); > } crashing_map SEC(".maps"); > SEC("kprobe/htab_map_get_next_key") > int trigger_crash(struct pt_regs *ctx) > { > int key =3D 0; > u64 *val =3D bpf_map_lookup_elem(&crashing_map, &key); > if (val) { > /* > * Trigger: Store a scalar (non-pointer) into a slot > * designated as a kptr. The verifier's map_kptr_match_type > * fails to handle the NULL reg->btf for scalars. > */ > *val =3D 0xdeadbeef; > } > return 0; > } > char LICENSE[] SEC("license") =3D "GPL"; > > ### Kernel Log Extract > [ 91.277247][ T7627] Oops: general protection fault, probably for > non-canonical address 0xdffffc0000I > [ 91.279715][ T7627] KASAN: null-ptr-deref in range > [0x00000000000000e8-0x00000000000000ef] > [ 91.280906][ T7627] CPU: 0 UID: 0 PID: 7627 Comm: bpftool Not > tainted 7.0.0-g1f5ffc672165 #5 PREEMPT(full) > [ 91.282421][ T7627] Hardware name: QEMU Standard PC (i440FX + PIIX, > 1996), BIOS 1.15.0-1 04/01/2014 > [ 91.283556][ T7627] RIP: 0010:btf_is_kernel+0x2a/0x50 > ... > > ### Actual Results > The kernel crashes during the verification phase. The verifier calls > `map_kptr_match_type`, which subsequently calls > `btf_is_kernel(reg->btf)`. Since the source register is a scalar, > `reg->btf` is NULL, leading to a NULL pointer dereference. > > Detailed info including reproducible BPF program and kernel logs have > been filed on Bugzilla: > > https://bugzilla.kernel.org/show_bug.cgi?id=3D221372 > > Please let me know if you need more information or if I can help test > a patch. Thanks for reporting the issue, I can reproduce it. Looks like a simple fix resolves is: diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9882475ee9da..91aa51a19c91 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -4544,6 +4544,9 @@ static int map_kptr_match_type(struct bpf_verifier_en= v *env, int perm_flags; const char *reg_name =3D ""; =20 + if (base_type(reg->type) !=3D PTR_TO_BTF_ID) + goto bad_type; + if (btf_is_kernel(reg->btf)) { perm_flags =3D PTR_MAYBE_NULL | PTR_TRUSTED | MEM_RCU; =20 @@ -4556,7 +4559,7 @@ static int map_kptr_match_type(struct bpf_verifier_en= v *env, perm_flags |=3D MEM_PERCPU; } =20 - if (base_type(reg->type) !=3D PTR_TO_BTF_ID || (type_flag(reg->type= ) & ~perm_flags)) + if (type_flag(reg->type) & ~perm_flags) goto bad_type;