From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7A9841D0F7D; Wed, 2 Oct 2024 14:06:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727877989; cv=none; b=UNQcIiuDHFJKqJWnFk1dOUk/rZ5kqqeK4G2L4E5v2BUZubu78vLKjfSTQT06CtdzqtTeJ7b1UT7mzeB4vxAKGz23cdPqVpHU3x4eVst11soVdSv2q0didRCKB2Ko3CLEFN7O+RDPfgeBcNit+iykRix/FAqKNKUrZOGz7warzwo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727877989; c=relaxed/simple; bh=QDftEfFzLeUxTOpZIHmoPAlHRMDqs/Vm+Ndtmcwp1YQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hNbZxFHr2U2vySG+zRyABlQ6SiWvrtXi/F2/X0qBuVIZZCfSOYcYQV8rX6P6JshhJyq032KUelKfGQs6oDW0QaH2o+sDZtRxUk0qTMIq1CkEV5hIeDMHMY7eiNhWOVtqIUGvC/JDvwXml1TTAd2JaOqkEsRZL67WaXna0e8+lXg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=n7cOw9+s; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="n7cOw9+s" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B334AC4CEC2; Wed, 2 Oct 2024 14:06:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1727877989; bh=QDftEfFzLeUxTOpZIHmoPAlHRMDqs/Vm+Ndtmcwp1YQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=n7cOw9+sOqbOmcT++XnLln20CgXIiHgxoMcAGo+92EWE/HCgs7AwRtw7p1pdaFU9p SbmEuQddeHNfr1KMx/QELGuH3f4C4LuwnXRfUXZuf5iGvY8BoyEAb5urhYDA8qx17F 07GQqc8xDaQdsfflksNTASDmggCbZ059kvzymRdM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+ad9ec60c8eaf69e6f99c@syzkaller.appspotmail.com, Eduard Zingerman , Yonghong Song , Alexei Starovoitov , Andrii Nakryiko , Sasha Levin Subject: [PATCH 6.10 236/634] bpf: Fail verification for sign-extension of packet data/data_end/data_meta Date: Wed, 2 Oct 2024 14:55:36 +0200 Message-ID: <20241002125820.413451072@linuxfoundation.org> X-Mailer: git-send-email 2.46.2 In-Reply-To: <20241002125811.070689334@linuxfoundation.org> References: <20241002125811.070689334@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.10-stable review patch. If anyone has any objections, please let me know. ------------------ 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/ 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 Signed-off-by: Sasha Levin --- 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 42b998518038a..b13af44f20ada 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -919,6 +919,7 @@ 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 203ce12e687d2..ed612052fc7ac 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5594,12 +5594,13 @@ 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, bool *is_retval) + struct btf **btf, u32 *btf_id, bool *is_retval, bool is_ldsx) { struct bpf_insn_access_aux info = { .reg_type = *reg_type, .log = &env->log, .is_retval = false, + .is_ldsx = is_ldsx, }; if (env->ops->is_valid_access && @@ -6913,7 +6914,7 @@ 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, &is_retval); + &btf_id, &is_retval, 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 55b1d9de2334d..bbcce4ddfb7bf 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -8568,13 +8568,16 @@ 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; @@ -9018,6 +9021,14 @@ 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) { @@ -9343,12 +9354,12 @@ 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; -- 2.43.0