From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dy2-f42.google.com (mail-dy2-f42.google.com [74.125.229.42]) (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 8BA313D9DAA for ; Tue, 29 Sep 2026 03:01:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.229.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790650900; cv=none; b=dMZD5QNyKYZYTeO9XS3oWIu3hmioC8swsTYAfFRjGZvqFaj8RIK+EcAtRBXkw1PtR238ihMxgs0uDTDHpWhS+IB85Hk6hA9myl7Ylr0QsSd5rjzT2IMTL9mlVbivYXnjcIatA3EC8RgFTSE/nUvXVGQHBz5m+JdEoR3oQ4nZAt8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790650900; c=relaxed/simple; bh=tjuHuJmSUWSzgdSY1MqrxhyhZbB4/rCV+kP6Py9vzxc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=tCEPUfYm+1bIxj55rK3mMAElHUyL60Hzi/5Uq2VnLXLMD5UXPEppN7K7GQXoWPBUdwwSm8ShzI7AkfWc0xOaw3AtwPACCD1Yda+nlp7IzrWriDPao5hVFWi5nLp2Ys90u872wn3iUufjr0D4TxlgmePA5nDreNttf0JWhL8TKw8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=trailofbits.com; spf=pass smtp.mailfrom=trailofbits.com; dkim=pass (2048-bit key) header.d=trailofbits.com header.i=@trailofbits.com header.b=Av2JwbfY; arc=none smtp.client-ip=74.125.229.42 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=trailofbits.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=trailofbits.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=trailofbits.com header.i=@trailofbits.com header.b="Av2JwbfY" Received: by mail-dy2-f42.google.com with SMTP id 5a478bee46e88-342568a5b54so1600708eec.2 for ; Mon, 28 Sep 2026 20:01:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=trailofbits.com; s=google; t=1790650893; x=1791255693; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to:content-type; bh=By2LEtvJF+8W3qvYb/dMgFvkCaBZwK3OmiKAlzBobDg=; b=Av2JwbfYQOAH73ibHQOh53j7ZTDzaN/fzE1EwOUPTZXX+zslX3tu6c1CKp4gBwHMsp 1VD6D+pfwz7XrWkagsvYyAKvfsUt7D9ouKScqddjpJGWBPBT0Qe+OmF1BqcDrz53GjFv z0Yu9gl9xfkIwjo2Elw5APPq+9PsuEdDfrSuHjb+p91WZYtsBZ7JY8u9OfafCV3+prsy rtIOlckiqnLZyLrVlBGK4bwh4vFybRFYOidBTMk5KQNaw2p5/9XKzPDI7W0raAsJd1a7 5HxwePHsklbQ1p/KAAoUOezZ784PL5gRCJPFnA167IksO6pUE+yQiVMHcqJnmYw6fhtc bXcw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790650893; x=1791255693; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=By2LEtvJF+8W3qvYb/dMgFvkCaBZwK3OmiKAlzBobDg=; b=hM0XNxupQLNMhIc2zeMEm7FGL7g1a2LSDD4MlIIV1P8tRudlQ2W48EMgPobIdbWYKx 4ei/ft9M8gkoelJP7mo3h9zNS+vz3i2+hYtmkLCAKr1INoIaXiEXBJUcVqniRdxOCRUd FaStUOrpuJHhsxiEeBNC2ay9XJBq2xl7kI5RgiYF1CDcwdp3fmpY4AZfPSmaaAnRe4/e zjN+Aa1xhgXOpi4n9+umJUyZkOhS/X6h81Dd+sAT97y6ihrvcmUuHL+vomC0BTJ+clVk ECA3cDbFlL66w30aDp2cze96E2rGiPlM3QAcz02/wop7jQlE51xIbdGz4I8+I7M862Zn byrw== X-Forwarded-Encrypted: i=1; AKwUvByEPFw6KdYCnrlxKdmzop4bFjAy1x8TS5Z/wn9/xWxeUzPfJr2uO+TrjGUwAx1ySYGbWzM=@vger.kernel.org X-Gm-Message-State: AFq9FYLdR+bJjOIjKs9/wOe7K9BEaBVtzhJqUiW78KYzgTMqdwDo1Es6 4IKPdSvRLcZ0+YAIiCQCPliwBr3Wj+g8Lvw5rRJbg0h9vBtnTs7l4gfiCTJYwqityg4= X-Gm-Gg: AYBFou1Jcz3zfomNX9XsVRHR7ufmOysx9TcHi80Tn2hReKQOmnhqilEHJZvBIjJZ/JK vvPUbYQroxXLCOBOsZBH/5G4TPVp64/xFB9KmZm0ncowlVNv3klOpQwosA2nJh8vKIo2T63yoMP +5Jpf2aVZbJqGSULMccI1RRxRwIoR9t8Hu+IiHQH7PIEdZsvxc2+tPUyOOVJl2zv2pyP5XZRXAe 9oWVr8a6reU+P92uDrkGUG4pqNRY+0+LcwfLUGO3oiCxT0DE1jX9w9YbXQM8CMFyuGtISFZ90Kj q0hGqvu9jyNfaRZNwFWY3+xBClSZFh+t2dINrKY3xjONQ4HbQ90Nn5yzIVzatJWLEuMN67QKWBB Z8ACyXPB9Sf7r4kB8CyVwj4dT/EHLiSLmpNCc0VsAxfC+zLJ6QMO0oPnGD9cmuo3IoQtjCdtlR9 y516I3wSKUkASQo0kYUDE266YplIF0OsqQd0LfhfAPhs4Ig872JFNhPkceX0wur7+nhQPqspcXY DRcc+DLnTIDtmjvnaSBNWAQC9Di/Hn+SzjGEisfhTZlUxgLqmmahNuWg/Q1YEF9BQp+INQ= X-Received: by 2002:a05:7300:a987:b0:33c:1f00:358 with SMTP id 5a478bee46e88-34270ac690bmr14894659eec.17.1790650893218; Mon, 28 Sep 2026 20:01:33 -0700 (PDT) Received: from localhost.localdomain ([2603:8001:5f01:8bab:3481:cbb6:f339:9e4e]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-347323f5a7esm10650314eec.15.2026.09.28.20.01.29 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Mon, 28 Sep 2026 20:01:32 -0700 (PDT) From: Artem Dinaburg To: stable@vger.kernel.org Cc: Artem Dinaburg , Greg Kroah-Hartman , Sasha Levin , Yonghong Song , syzbot+ad9ec60c8eaf69e6f99c@syzkaller.appspotmail.com, Eduard Zingerman , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , John Fastabend , Martin KaFai Lau , Song Liu , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Jesper Dangaard Brouer , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, Kumar Kartikeya Dwivedi , Emil Tsalapatis , Ihor Solodrai , Simon Horman , sdf@google.com Subject: [PATCH 6.6.y] bpf: Fail verification for sign-extension of packet data/data_end/data_meta Date: Mon, 28 Sep 2026 23:01:25 -0400 Message-ID: <20260929030127.86206-1-artem@trailofbits.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Yonghong Song [ Upstream commit 92de36080c93296ef9005690705cba260b9bd68a ] syzbot reported a kernel crash due to commit 1f1e864b6555 ("bpf: Handle sign-extenstin ctx member accesses"). The reason is due to sign-extension of 32-bit load for packet data/data_end/data_meta uapi field. The original code looks like: r2 = *(s32 *)(r1 + 76) /* load __sk_buff->data */ r3 = *(u32 *)(r1 + 80) /* load __sk_buff->data_end */ r0 = r2 r0 += 8 if r3 > r0 goto +1 ... Note that __sk_buff->data load has 32-bit sign extension. After verification and convert_ctx_accesses(), the final asm code looks like: r2 = *(u64 *)(r1 +208) r2 = (s32)r2 r3 = *(u64 *)(r1 +80) r0 = r2 r0 += 8 if r3 > r0 goto pc+1 ... Note that 'r2 = (s32)r2' may make the kernel __sk_buff->data address invalid which may cause runtime failure. Currently, in C code, typically we have void *data = (void *)(long)skb->data; void *data_end = (void *)(long)skb->data_end; ... and it will generate r2 = *(u64 *)(r1 +208) r3 = *(u64 *)(r1 +80) r0 = r2 r0 += 8 if r3 > r0 goto pc+1 If we allow sign-extension, void *data = (void *)(long)(int)skb->data; void *data_end = (void *)(long)skb->data_end; ... the generated code looks like r2 = *(u64 *)(r1 +208) r2 <<= 32 r2 s>>= 32 r3 = *(u64 *)(r1 +80) r0 = r2 r0 += 8 if r3 > r0 goto pc+1 and this will cause verification failure since "r2 <<= 32" is not allowed as "r2" is a packet pointer. To fix this issue for case r2 = *(s32 *)(r1 + 76) /* load __sk_buff->data */ this patch added additional checking in is_valid_access() callback function for packet data/data_end/data_meta access. If those accesses are with sign-extenstion, the verification will fail. [1] https://lore.kernel.org/bpf/000000000000c90eee061d236d37@google.com/ [ Backport to 6.6.y: implemented the packet-field check without the newer is_retval verifier API. ] Reported-by: syzbot+ad9ec60c8eaf69e6f99c@syzkaller.appspotmail.com Fixes: 1f1e864b6555 ("bpf: Handle sign-extenstin ctx member accesses") Acked-by: Eduard Zingerman Signed-off-by: Yonghong Song Link: https://lore.kernel.org/r/20240723153439.2429035-1-yonghong.song@linux.dev Signed-off-by: Alexei Starovoitov Signed-off-by: Andrii Nakryiko Assisted-by: LLM Signed-off-by: Artem Dinaburg --- Hi Greg, Sasha, and bpf maintainers, I am working through the small CVE backports still missing from 6.6.y. This one addresses CVE-2024-47702. It rejects sign-extended loads that can turn packet pointers into invalid addresses. The fix is already present in 6.12.y, 6.18.y, and 7.2.y, but not in 6.6.y. The target-specific adjustment is recorded in the bracketed note above. Could you please queue it for 6.6.y? CVE: CVE-2024-47702 Upstream: 92de36080c93296ef9005690705cba260b9bd68a AI assistance: An LLM helped identify, adapt, and validate this backport; I reviewed the resulting code and validation evidence. Thanks, Artem Dinaburg include/linux/bpf.h | 1 + kernel/bpf/verifier.c | 5 +++-- net/core/filter.c | 21 ++++++++++++++++----- 3 files changed, 20 insertions(+), 7 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index fd20812cbcc331..1b2f3c94365e72 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -929,6 +929,7 @@ static_assert(__BPF_REG_TYPE_MAX <= BPF_BASE_TYPE_LIMIT); */ struct bpf_insn_access_aux { enum bpf_reg_type reg_type; + bool is_ldsx; union { int ctx_field_size; struct { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f7f5f54dc44852..46c205087160c2 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5664,11 +5664,12 @@ static int check_packet_access(struct bpf_verifier_env *env, u32 regno, int off, /* check access to 'struct bpf_context' fields. Supports fixed offsets only */ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off, int size, enum bpf_access_type t, enum bpf_reg_type *reg_type, - struct btf **btf, u32 *btf_id) + struct btf **btf, u32 *btf_id, bool is_ldsx) { struct bpf_insn_access_aux info = { .reg_type = *reg_type, .log = &env->log, + .is_ldsx = is_ldsx, }; if (env->ops->is_valid_access && @@ -6917,7 +6918,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn return err; err = check_ctx_access(env, insn_idx, off, size, t, ®_type, &btf, - &btf_id); + &btf_id, is_ldsx); if (err) verbose_linfo(env, insn_idx, "; "); if (!err && t == BPF_READ && value_regno >= 0) { diff --git a/net/core/filter.c b/net/core/filter.c index f568006baafa8a..bcf1f453f0373a 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -8631,13 +8631,16 @@ static bool bpf_skb_is_valid_access(int off, int size, enum bpf_access_type type if (off + size > offsetofend(struct __sk_buff, cb[4])) return false; break; + case bpf_ctx_range(struct __sk_buff, data): + case bpf_ctx_range(struct __sk_buff, data_meta): + case bpf_ctx_range(struct __sk_buff, data_end): + if (info->is_ldsx || size != size_default) + return false; + break; case bpf_ctx_range_till(struct __sk_buff, remote_ip6[0], remote_ip6[3]): case bpf_ctx_range_till(struct __sk_buff, local_ip6[0], local_ip6[3]): case bpf_ctx_range_till(struct __sk_buff, remote_ip4, remote_ip4): case bpf_ctx_range_till(struct __sk_buff, local_ip4, local_ip4): - case bpf_ctx_range(struct __sk_buff, data): - case bpf_ctx_range(struct __sk_buff, data_meta): - case bpf_ctx_range(struct __sk_buff, data_end): if (size != size_default) return false; break; @@ -9081,6 +9084,14 @@ static bool xdp_is_valid_access(int off, int size, } } return false; + } else { + switch (off) { + case offsetof(struct xdp_md, data_meta): + case offsetof(struct xdp_md, data): + case offsetof(struct xdp_md, data_end): + if (info->is_ldsx) + return false; + } } switch (off) { @@ -9413,12 +9424,12 @@ static bool flow_dissector_is_valid_access(int off, int size, switch (off) { case bpf_ctx_range(struct __sk_buff, data): - if (size != size_default) + if (info->is_ldsx || size != size_default) return false; info->reg_type = PTR_TO_PACKET; return true; case bpf_ctx_range(struct __sk_buff, data_end): - if (size != size_default) + if (info->is_ldsx || size != size_default) return false; info->reg_type = PTR_TO_PACKET_END; return true; -- 2.39.5