From patchwork Wed Oct 6 16:02:41 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: YiFei Zhu X-Patchwork-Id: 12539695 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FCC8C4332F for ; Wed, 6 Oct 2021 16:03:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 74A61610C8 for ; Wed, 6 Oct 2021 16:03:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232622AbhJFQEy (ORCPT ); Wed, 6 Oct 2021 12:04:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59848 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230021AbhJFQEy (ORCPT ); Wed, 6 Oct 2021 12:04:54 -0400 Received: from mail-pl1-x62f.google.com (mail-pl1-x62f.google.com [IPv6:2607:f8b0:4864:20::62f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D6E56C061746 for ; Wed, 6 Oct 2021 09:03:01 -0700 (PDT) Received: by mail-pl1-x62f.google.com with SMTP id y1so1929534plk.10 for ; Wed, 06 Oct 2021 09:03:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=P04QJ/4Y946HO6LTkPlGTPEfscMIc2EXyiWAONPvzpo=; b=ESP7gPDaoBIaUDS6EInNcY0cPoPb3dD5k0rkI11rjbqwlfAfzXAVfF8l+2fO4zk0yD 1i7EIfwozYAJhe1AC981jOrAC8au1oLkm/7IPqPzIC0oQ/Q/arTEAtn/2AkH6HQhRJLY 6u6lGWSde3iJB8+Hlspzf9xPu+Z/nMtPE5sJYMeCeBsSOPXmx94KtL4IYC4iRBsaxGnF zEM4Bj76bYbEGyn+0/XSQMCDWBpSd2g/V/tTwtOX3e++1OaWXJY1VYbElX1QU65EHtSH 68UX5vDwm7MDnuv7+Z0rwy1jKMHOiW64VmzS+5SmENpdCDyn+BCY2ItEjTgMTfEO5dg4 V8WQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=P04QJ/4Y946HO6LTkPlGTPEfscMIc2EXyiWAONPvzpo=; b=0Rp+0nTx1Kl7Az9hnxqbFqvmNf+OMkxyFbrYX7TFyFkscJAjC7n/c8q1Kq6j1n5Zb/ YUKFI/d8RKJNJe40vUitbajgpQ//x3mQaq9YvQLxbXbtB3kACOgARZqp1zNGX8zmgLQm SX2HwGODqKrAN9fU/+oj0B93ShQvwTj3kNxR7y9xJ8d7ftox8FCtSRRZawL0Kqg1OQ+4 JFW1cD+nJ59k1cwPMPAzBsjYjKHlnVmEt93TvabbTmQ+3ueHUdkqWpQ+DKSIrKys933s ZRTENSG9Mly778GnRVDZ1wyLFtZM2Zyuitr3MQg71SHan08ZMmVegU3yBUTwoe/kAZ/8 h8rA== X-Gm-Message-State: AOAM532kV4y5V8iI7K2VkTXAg0T/Sx39eGpGf/nXJDYhzr7DFmLcLh2D 1F+UlOBuu9Tz2Uo6+GQCHG2xXWfJgaE= X-Google-Smtp-Source: ABdhPJxxFB4ysEW29pPcO5bp2WCEzUeSKXdjgcqkvA/dKY+/hq0Dka6ykLdB5lH9bvyX+VpwCqvqpA== X-Received: by 2002:a17:90a:5895:: with SMTP id j21mr11679165pji.99.1633536181151; Wed, 06 Oct 2021 09:03:01 -0700 (PDT) Received: from localhost.localdomain ([98.47.144.235]) by smtp.gmail.com with ESMTPSA id x19sm20906098pfn.105.2021.10.06.09.03.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Oct 2021 09:03:00 -0700 (PDT) From: YiFei Zhu To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Stanislav Fomichev , YiFei Zhu Subject: [PATCH bpf-next 2/3] bpf: Add cgroup helper bpf_export_errno to get/set exported errno value Date: Wed, 6 Oct 2021 09:02:41 -0700 Message-Id: X-Mailer: git-send-email 2.33.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net From: YiFei Zhu When passed in a positive errno, it sets the errno and returns 0. When passed in 0, it gets the previously set errno. When passed in an out of bound number, it returns -EINVAL. This is unambiguous: negative return values are error in invoking the helper itself, and positive return values are errnos being exported. Errnos once set cannot be unset, but can be overridden. The errno value is stored inside bpf_cg_run_ctx for ease of access different prog types with different context structs layouts. The helper implementation can simply perform a container_of from current->bpf_ctx to retrieve bpf_cg_run_ctx. For backward compatibility, if a program rejects without calling the helper, and the errno has not been set by any prior progs, the BPF_PROG_RUN_ARRAY_CG family macros automatically set the errno to EPERM. If a prog sets an errno but returns 1 (allow), the outcome is considered implementation-defined. This patch treat it the same way as if 0 (reject) is returned. For BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY, the prior behavior is that, if the return value is NET_XMIT_DROP, the packet is silently dropped. We preserve this behavior for backward compatibility reasons, so even if an errno is set, the errno does not return to caller. For getsockopt hooks, they are different in that bpf progs runs after kernel processes the getsockopt syscall instead of before. There is also a retval in its context struct in which bpf progs can unset the retval, and can force an -EPERM by returning 0. We preseve the same semantics. Even though there is retval, that value can only be unset, while progs can set (and not unset) additional errno by using the helper, and that will override whatever is in retval. Signed-off-by: YiFei Zhu Reviewed-by: Stanislav Fomichev Acked-by: Song Liu --- include/linux/bpf.h | 23 +++++++++++------------ include/uapi/linux/bpf.h | 14 ++++++++++++++ kernel/bpf/cgroup.c | 24 ++++++++++++++++++++++++ tools/include/uapi/linux/bpf.h | 14 ++++++++++++++ 4 files changed, 63 insertions(+), 12 deletions(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 938885562d68..5e3f3d2f5871 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1155,6 +1155,7 @@ struct bpf_run_ctx {}; struct bpf_cg_run_ctx { struct bpf_run_ctx run_ctx; const struct bpf_prog_array_item *prog_item; + int errno_val; }; struct bpf_trace_run_ctx { @@ -1196,8 +1197,7 @@ BPF_PROG_RUN_ARRAY_CG_FLAGS(const struct bpf_prog_array __rcu *array_rcu, const struct bpf_prog *prog; const struct bpf_prog_array *array; struct bpf_run_ctx *old_run_ctx; - struct bpf_cg_run_ctx run_ctx; - int ret = 0; + struct bpf_cg_run_ctx run_ctx = {}; u32 func_ret; migrate_disable(); @@ -1208,15 +1208,15 @@ BPF_PROG_RUN_ARRAY_CG_FLAGS(const struct bpf_prog_array __rcu *array_rcu, while ((prog = READ_ONCE(item->prog))) { run_ctx.prog_item = item; func_ret = run_prog(prog, ctx); - if (!(func_ret & 1)) - ret = -EPERM; + if (!(func_ret & 1) && !run_ctx.errno_val) + run_ctx.errno_val = EPERM; *(ret_flags) |= (func_ret >> 1); item++; } bpf_reset_run_ctx(old_run_ctx); rcu_read_unlock(); migrate_enable(); - return ret; + return -run_ctx.errno_val; } static __always_inline int @@ -1227,8 +1227,7 @@ BPF_PROG_RUN_ARRAY_CG(const struct bpf_prog_array __rcu *array_rcu, const struct bpf_prog *prog; const struct bpf_prog_array *array; struct bpf_run_ctx *old_run_ctx; - struct bpf_cg_run_ctx run_ctx; - int ret = 0; + struct bpf_cg_run_ctx run_ctx = {}; migrate_disable(); rcu_read_lock(); @@ -1237,14 +1236,14 @@ BPF_PROG_RUN_ARRAY_CG(const struct bpf_prog_array __rcu *array_rcu, old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx); while ((prog = READ_ONCE(item->prog))) { run_ctx.prog_item = item; - if (!run_prog(prog, ctx)) - ret = -EPERM; + if (!run_prog(prog, ctx) && !run_ctx.errno_val) + run_ctx.errno_val = EPERM; item++; } bpf_reset_run_ctx(old_run_ctx); rcu_read_unlock(); migrate_enable(); - return ret; + return -run_ctx.errno_val; } static __always_inline u32 @@ -1297,7 +1296,7 @@ BPF_PROG_RUN_ARRAY(const struct bpf_prog_array __rcu *array_rcu, * 0: NET_XMIT_SUCCESS skb should be transmitted * 1: NET_XMIT_DROP skb should be dropped and cn * 2: NET_XMIT_CN skb should be transmitted and cn - * 3: -EPERM skb should be dropped + * 3: -errno skb should be dropped */ #define BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY(array, ctx, func) \ ({ \ @@ -1309,7 +1308,7 @@ BPF_PROG_RUN_ARRAY(const struct bpf_prog_array __rcu *array_rcu, if (!_ret) \ _ret = (_cn ? NET_XMIT_CN : NET_XMIT_SUCCESS); \ else \ - _ret = (_cn ? NET_XMIT_DROP : -EPERM); \ + _ret = (_cn ? NET_XMIT_DROP : _ret); \ _ret; \ }) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index 6fc59d61937a..d8126f8c0541 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -4909,6 +4909,19 @@ union bpf_attr { * Return * The number of bytes written to the buffer, or a negative error * in case of failure. + * + * int bpf_export_errno(int errno_val) + * Description + * If *errno_val* is positive, set the syscall's return error code; + * if *errno_val* is zero, retrieve the previously set code. + * + * This helper is currently supported by cgroup programs only. + * Return + * Zero if set is successful, or the previously set error code on + * retrieval. Previously set code may be zero if it was never set. + * On error, a negative value. + * + * **-EINVAL** if *errno_val* not between zero and MAX_ERRNO inclusive. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -5089,6 +5102,7 @@ union bpf_attr { FN(task_pt_regs), \ FN(get_branch_snapshot), \ FN(trace_vprintk), \ + FN(export_errno), \ /* */ /* integer value in 'imm' field of BPF_CALL instruction selects which helper diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c index 5efe2588575e..5b5051eb43e6 100644 --- a/kernel/bpf/cgroup.c +++ b/kernel/bpf/cgroup.c @@ -1169,6 +1169,28 @@ int __cgroup_bpf_check_dev_permission(short dev_type, u32 major, u32 minor, return ret; } +BPF_CALL_1(bpf_export_errno, int, errno_val) +{ + struct bpf_cg_run_ctx *ctx = + container_of(current->bpf_ctx, struct bpf_cg_run_ctx, run_ctx); + + if (errno_val < 0 || errno_val > MAX_ERRNO) + return -EINVAL; + + if (!errno_val) + return ctx->errno_val; + + ctx->errno_val = errno_val; + return 0; +} + +static const struct bpf_func_proto bpf_export_errno_proto = { + .func = bpf_export_errno, + .gpl_only = false, + .ret_type = RET_INTEGER, + .arg1_type = ARG_ANYTHING, +}; + static const struct bpf_func_proto * cgroup_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) { @@ -1181,6 +1203,8 @@ cgroup_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &bpf_get_current_cgroup_id_proto; case BPF_FUNC_perf_event_output: return &bpf_event_output_data_proto; + case BPF_FUNC_export_errno: + return &bpf_export_errno_proto; default: return bpf_base_func_proto(func_id); } diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index 6fc59d61937a..d8126f8c0541 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -4909,6 +4909,19 @@ union bpf_attr { * Return * The number of bytes written to the buffer, or a negative error * in case of failure. + * + * int bpf_export_errno(int errno_val) + * Description + * If *errno_val* is positive, set the syscall's return error code; + * if *errno_val* is zero, retrieve the previously set code. + * + * This helper is currently supported by cgroup programs only. + * Return + * Zero if set is successful, or the previously set error code on + * retrieval. Previously set code may be zero if it was never set. + * On error, a negative value. + * + * **-EINVAL** if *errno_val* not between zero and MAX_ERRNO inclusive. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -5089,6 +5102,7 @@ union bpf_attr { FN(task_pt_regs), \ FN(get_branch_snapshot), \ FN(trace_vprintk), \ + FN(export_errno), \ /* */ /* integer value in 'imm' field of BPF_CALL instruction selects which helper