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Sat, 24 Oct 2026 18:19:18 -0700 (PDT) Received: from localhost ([153.61.198.249]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3adeba32f70sm3963081a91.1.2026.10.24.18.19.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 24 Oct 2026 18:19:17 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Sun, 25 Oct 2026 01:19:16 +0000 Message-Id: Cc: "Andrew Lunn" , "David S . Miller" , "Eric Dumazet" , "Jakub Kicinski" , "Paolo Abeni" , "Simon Horman" , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Emil Tsalapatis" , "Ihor Solodrai" , "Jesper Dangaard Brouer" , "John Fastabend" , "Stanislav Fomichev" , "Steven Rostedt" , "Masami Hiramatsu" , "Mathieu Desnoyers" , "Shuah Khan" , "Kuniyuki Iwashima" , "Hangbin Liu" , "Martin Karsten" , "Masashi Honma" , , , , Subject: Re: [PATCH bpf-next v4 2/6] bpf: Add syscall common attrs support for xdp link_create From: "Alexei Starovoitov" To: "Leon Hwang" , In-Reply-To: <20261024153608.58569-3-leon.hwang@linux.dev> References: <20261024153608.58569-1-leon.hwang@linux.dev> <20261024153608.58569-3-leon.hwang@linux.dev> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Sat, Oct 24, 2026 at 08:36 AM Leon Hwang wrote: > Instead of passing bpf log or extack to bpf_xdp_link_attach(), pass an > errmsg pointer to receive the kstrdup() error msg, because [...] > 2) passing extack will access underlying driver string out of dev_put() > guard, which will crash kernel when the device is unloaded > concurrently. Netlink does exactly that. rtnl_setlink() looks up the dev with __dev_get_by_index(), so no refcnt, do_setlink() -> dev_change_xdp_fd(dev, extack, ...) calls into the same drivers that set the same strings, rtnl is unlocked, and only then netlink_rcv_skb() -> netlink_ack() does strlen(extack->_msg). All extack users work this way. kstrdup() in one of them fixes nothing. Instead of patches 1 and 2: diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index c0ae442..6f7fec2 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -4440,7 +4440,8 @@ struct sk_buff *validate_xmit_skb_list(struct sk_buff *skb, struct net_device *d struct sk_buff *dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev, struct netdev_queue *txq, int *ret); -int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog); +int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog, + struct netlink_ext_ack *extack); u8 dev_xdp_prog_count(struct net_device *dev); int netif_xdp_propagate(struct net_device *dev, struct netdev_bpf *bpf); int dev_xdp_propagate(struct net_device *dev, struct netdev_bpf *bpf); diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 90bc723..0ce75ee 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -5862,8 +5862,12 @@ err_put: } #define BPF_LINK_CREATE_LAST_FIELD link_create.uprobe_multi.path_fd -static int link_create(union bpf_attr *attr, bpfptr_t uattr) +static int link_create(union bpf_attr *attr, bpfptr_t uattr, struct bpf_common_attr *attr_common, + bpfptr_t uattr_common, u32 size_common) { + struct netlink_ext_ack extack = {}; + struct bpf_verifier_log *log; + struct bpf_log_attr attr_log; struct bpf_prog *prog; int ret; @@ -5873,14 +5877,24 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr) if (attr->link_create.attach_type == BPF_STRUCT_OPS) return bpf_struct_ops_link_create(attr); + log = bpf_log_attr_create_vlog(&attr_log, attr_common, uattr_common, size_common); + if (IS_ERR(log)) + return PTR_ERR(log); + prog = bpf_prog_get(attr->link_create.prog_fd); - if (IS_ERR(prog)) - return PTR_ERR(prog); + if (IS_ERR(prog)) { + bpf_log(log, "Invalid prog_fd.\n"); + ret = PTR_ERR(prog); + prog = NULL; + goto out; + } ret = bpf_prog_attach_check_attach_type(prog, attr->link_create.attach_type); - if (ret) + if (ret) { + bpf_log(log, "Invalid attach_type.\n"); goto out; + } switch (prog->type) { case BPF_PROG_TYPE_CGROUP_SKB: @@ -5931,7 +5945,7 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr) break; #ifdef CONFIG_NET case BPF_PROG_TYPE_XDP: - ret = bpf_xdp_link_attach(attr, prog); + ret = bpf_xdp_link_attach(attr, prog, &extack); break; case BPF_PROG_TYPE_SCHED_CLS: if (attr->link_create.attach_type == BPF_TCX_INGRESS || @@ -5959,12 +5973,22 @@ static int link_create(union bpf_attr *attr, bpfptr_t uattr) ret = bpf_uprobe_multi_link_attach(attr, prog); break; default: + bpf_log(log, "Invalid prog type.\n"); ret = -EINVAL; } out: - if (ret < 0) - bpf_prog_put(prog); + if (ret < 0) { + int err; + + if (extack._msg) + bpf_log(log, "%s\n", extack._msg); + err = bpf_log_attr_finalize(&attr_log, log); + ret = err ? err : ret; + if (prog) + bpf_prog_put(prog); + } + kfree(log); return ret; } @@ -6536,7 +6560,7 @@ static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size, err = bpf_map_do_batch(&attr, uattr.user, BPF_MAP_DELETE_BATCH); break; case BPF_LINK_CREATE: - err = link_create(&attr, uattr); + err = link_create(&attr, uattr, &attr_common, uattr_common, size_common); break; case BPF_LINK_UPDATE: err = link_update(&attr); diff --git a/net/core/dev.c b/net/core/dev.c index 1a09e78..4aa5525 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -10882,11 +10882,11 @@ static const struct bpf_link_ops bpf_xdp_link_lops = { .update_prog = bpf_xdp_link_update, }; -int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) +int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog, + struct netlink_ext_ack *extack) { struct net *net = current->nsproxy->net_ns; struct bpf_link_primer link_primer; - struct netlink_ext_ack extack = {}; struct bpf_xdp_link *link; struct net_device *dev; int err, fd; @@ -10895,6 +10895,7 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) dev = dev_get_by_index(net, attr->link_create.target_ifindex); if (!dev) { rtnl_unlock(); + NL_SET_ERR_MSG(extack, "Invalid target_ifindex."); return -EINVAL; } @@ -10916,14 +10917,14 @@ int bpf_xdp_link_attach(const union bpf_attr *attr, struct bpf_prog *prog) } netdev_lock_ops(dev); - err = dev_xdp_attach_link(dev, &extack, link); + err = dev_xdp_attach_link(dev, extack, link); netdev_unlock_ops(dev); rtnl_unlock(); if (err) { link->dev = NULL; bpf_link_cleanup(&link_primer); - trace_bpf_xdp_link_attach_failed(extack._msg); + trace_bpf_xdp_link_attach_failed(extack->_msg); goto out_put_dev; } I'm think I gave this suggestion earlier. Why did you go with strdup()? pw-bot: cr