syzbot reported a circular locking dependency involving &net->xdp.lock, &xs->mutex, and netdev_lock_ops(): -> #2 (&net->xdp.lock): xsk_diag_dump netlink_dump -> #1 (&xs->mutex): xsk_bind -> #0 (netdev_lock_ops): xsk_notifier The lockdep dependency cycle arose from the following relationships: - xsk_diag_dump() established &net->xdp.lock -> &xs->mutex by calling xsk_diag_fill() under &net->xdp.lock. - xsk_bind() established &xs->mutex -> netdev_lock_ops(). - Device unregistration and xsk_notifier() established netdev_lock_ops() -> &net->xdp.lock while also invoking xp_clear_dev() under &net->xdp.lock and &xs->mutex. Eliminate the cycle by decoupling the locks across both paths: 1. In xsk_notifier(), split the unregistration into two phases: - First, unbind all matching sockets under &net->xdp.lock and &xs->mutex. - Then, release &net->xdp.lock and perform device queue teardown by sweeping the device queues via xsk_get_pool_from_qid() and calling xp_clear_dev(pool) outside all AF_XDP locks. 2. In xsk_diag_dump(), avoid holding &net->xdp.lock while calling xsk_diag_fill(). Instead, locate the target socket under &net->xdp.lock, take a temporary socket reference via sock_hold(), release &net->xdp.lock, and call xsk_diag_fill() (which acquires &xs->mutex) with sock_put(). Distinguish -ENOENT (when an unbound socket is skipped) from -EMSGSIZE (when the skb is full and the cursor must be retained for dump continuation). Fixes: 975b11ae9077 ("xsk: add socket allocate, create and bind") Reported-by: syzbot+aa48b5fe7bfda62d1682@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=aa48b5fe7bfda62d1682 Signed-off-by: Khawar Ahemad --- v2 -> v3: - Fix direct AB-BA lock inversion in xsk_notifier() by performing device queue sweeps via xsk_get_pool_from_qid() outside &net->xdp.lock. - Eliminate &net->xdp.lock -> &xs->mutex in xsk_diag_dump() by taking a temporary socket reference under &net->xdp.lock and releasing the lock prior to xsk_diag_fill(). - Distinguish -ENOENT (skipped unbound socket) from -EMSGSIZE (buffer exhaustion) to preserve dump continuation without infinite loops. - Link to v2: https://lore.kernel.org/bpf/20260826162110.99879-1-ahemadkhawar123@gmail.com/ v1 -> v2: - Avoid reordering locks in xsk_bind() to preserve errno precedence. - Link to v1: https://lore.kernel.org/bpf/20260825152152.86092-1-ahemadkhawar123@gmail.com/ net/xdp/xsk.c | 17 +++++++----- net/xdp/xsk_diag.c | 65 +++++++++++++++++++++++++++++++--------------- 2 files changed, 55 insertions(+), 27 deletions(-) diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index c2f47182dc..e72344fccb 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -2099,14 +2099,15 @@ static int xsk_notifier(struct notifier_block *this, { struct net_device *dev = netdev_notifier_info_to_dev(ptr); struct net *net = dev_net(dev); + unsigned int max_queues; struct sock *sk; + u16 qid; switch (msg) { case NETDEV_UNREGISTER: mutex_lock(&net->xdp.lock); sk_for_each(sk, &net->xdp.list) { struct xdp_sock *xs = xdp_sk(sk); - struct xsk_buff_pool *pool = NULL; mutex_lock(&xs->mutex); if (xs->dev == dev) { @@ -2114,18 +2115,22 @@ static int xsk_notifier(struct notifier_block *this, if (!sock_flag(sk, SOCK_DEAD)) sk_error_report(sk); - pool = xs->pool; xsk_unbind_dev(xs); } mutex_unlock(&xs->mutex); + } + mutex_unlock(&net->xdp.lock); + + /* Clear device references outside AF_XDP locks to avoid + * lock inversion with netdev_lock_ops(). + */ + max_queues = max(dev->real_num_rx_queues, dev->real_num_tx_queues); + for (qid = 0; qid < max_queues; qid++) { + struct xsk_buff_pool *pool = xsk_get_pool_from_qid(dev, qid); - /* Clear device references outside xs->mutex to avoid - * lock inversion with netdev_lock_ops(). - */ if (pool) xp_clear_dev(pool); } - mutex_unlock(&net->xdp.lock); break; } return NOTIFY_DONE; diff --git a/net/xdp/xsk_diag.c b/net/xdp/xsk_diag.c index 0170363eb5..bad0b13064 100644 --- a/net/xdp/xsk_diag.c +++ b/net/xdp/xsk_diag.c @@ -97,6 +97,7 @@ static int xsk_diag_fill(struct sock *sk, struct sk_buff *nlskb, struct xdp_sock *xs = xdp_sk(sk); struct xdp_diag_msg *msg; struct nlmsghdr *nlh; + int err = -EMSGSIZE; nlh = nlmsg_put(nlskb, portid, seq, SOCK_DIAG_BY_FAMILY, sizeof(*msg), flags); @@ -111,8 +112,10 @@ static int xsk_diag_fill(struct sock *sk, struct sk_buff *nlskb, sock_diag_save_cookie(sk, msg->xdiag_cookie); mutex_lock(&xs->mutex); - if (READ_ONCE(xs->state) == XSK_UNBOUND) + if (READ_ONCE(xs->state) == XSK_UNBOUND) { + err = -ENOENT; goto out_nlmsg_trim; + } if ((req->xdiag_show & XDP_SHOW_INFO) && xsk_diag_put_info(xs, nlskb)) goto out_nlmsg_trim; @@ -145,7 +148,7 @@ static int xsk_diag_fill(struct sock *sk, struct sk_buff *nlskb, out_nlmsg_trim: mutex_unlock(&xs->mutex); nlmsg_cancel(nlskb, nlh); - return -EMSGSIZE; + return err; } static int xsk_diag_dump(struct sk_buff *nlskb, struct netlink_callback *cb) @@ -153,28 +156,48 @@ static int xsk_diag_dump(struct sk_buff *nlskb, struct netlink_callback *cb) struct xdp_diag_req *req = nlmsg_data(cb->nlh); struct net *net = sock_net(nlskb->sk); int num = 0, s_num = cb->args[0]; - struct sock *sk; - - mutex_lock(&net->xdp.lock); - - sk_for_each(sk, &net->xdp.list) { - if (!net_eq(sock_net(sk), net)) - continue; - if (num++ < s_num) - continue; - - if (xsk_diag_fill(sk, nlskb, req, - sk_user_ns(NETLINK_CB(cb->skb).sk), - NETLINK_CB(cb->skb).portid, - cb->nlh->nlmsg_seq, NLM_F_MULTI, - sock_i_ino(sk)) < 0) { - num--; - break; + struct sock *sk, *target_sk; + int err; + + for (;;) { + target_sk = NULL; + num = 0; + + mutex_lock(&net->xdp.lock); + sk_for_each(sk, &net->xdp.list) { + if (!net_eq(sock_net(sk), net)) + continue; + if (num++ == s_num) { + sock_hold(sk); + target_sk = sk; + break; + } } + mutex_unlock(&net->xdp.lock); + + if (!target_sk) + break; + + err = xsk_diag_fill(target_sk, nlskb, req, + sk_user_ns(NETLINK_CB(cb->skb).sk), + NETLINK_CB(cb->skb).portid, + cb->nlh->nlmsg_seq, NLM_F_MULTI, + sock_i_ino(target_sk)); + sock_put(target_sk); + + /* + * xsk_diag_fill() returns: + * 0: entry added successfully. + * -ENOENT: socket is unbound, skip it. + * -EMSGSIZE: skb is full, retry this socket on the next dump callback. + */ + if (err == -EMSGSIZE) + break; + + s_num++; } - mutex_unlock(&net->xdp.lock); - cb->args[0] = num; + cb->args[0] = s_num; return nlskb->len; } -- 2.54.0 (Apple Git-157)