From ab1513597c6cf17cd1ad2a21e3b045421b48e022 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Safa=20Karaku=C5=9F?= Date: Sat, 16 May 2026 21:15:04 +0300 Subject: [PATCH] Bluetooth: fix UAF in l2cap_sock_cleanup_listen() vs l2cap_conn_del() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit bt_accept_dequeue() unlinks a not-yet-accepted child from the parent accept queue and release_sock()s it before returning, so the returned sk has no caller reference and is unlocked. l2cap_sock_cleanup_listen() walks these children on listening-socket close. A concurrent HCI disconnect drives hci_rx_work -> l2cap_conn_del() which runs l2cap_chan_del() + l2cap_sock_kill() and frees the child sk and its l2cap_chan; cleanup_listen() then uses both: BUG: KASAN: slab-use-after-free in l2cap_sock_kill l2cap_sock_kill / l2cap_sock_cleanup_listen / __x64_sys_close Freed by: l2cap_conn_del -> l2cap_sock_close_cb -> l2cap_sock_kill This is distinct from the two fixes already in this area: commit e83f5e24da741 ("Bluetooth: serialize accept_q access") serialises the accept_q list/poll and takes temporary refs inside bt_accept_dequeue(), and CVE-2025-39860 serialises the userspace close()/accept() race by calling cleanup_listen() under lock_sock() in l2cap_sock_release(). Neither covers l2cap_conn_del() running from hci_rx_work, so this UAF still reproduces on current bluetooth/master. Take the reference at the source: bt_accept_dequeue() does sock_hold() while sk is still locked, before release_sock(); callers sock_put(). cleanup_listen() pins the chan with l2cap_chan_hold_unless_zero() under a brief child sk lock (serialising vs l2cap_sock_teardown_cb()), drops it before l2cap_chan_lock(), and skips a duplicate l2cap_sock_kill() on SOCK_DEAD. conn->lock is not taken here: cleanup_listen() runs under the parent sk lock and that would invert conn->lock -> chan->lock -> sk_lock (lockdep). KASAN/SMP: an unprivileged listen/close vs HCI-disconnect race produced 12 use-after-free reports per run before this change; 0, and no lockdep report, over 1600+ raced iterations after it on bluetooth/master. Fixes: 15f02b910562 ("Bluetooth: L2CAP: Add initial code for Enhanced Credit Based Mode") Cc: stable@vger.kernel.org Reported-by: Siwei Zhang Reviewed-by: Siwei Zhang Signed-off-by: Safa Karakuş Signed-off-by: Luiz Augusto von Dentz --- net/bluetooth/af_bluetooth.c | 10 +++++++ net/bluetooth/iso.c | 9 ++++++- net/bluetooth/l2cap_sock.c | 51 +++++++++++++++++++++++++++++++----- net/bluetooth/rfcomm/sock.c | 9 ++++++- net/bluetooth/sco.c | 9 ++++++- 5 files changed, 78 insertions(+), 10 deletions(-) diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c index 9d68dd86023c..1a6aa3f8d4d6 100644 --- a/net/bluetooth/af_bluetooth.c +++ b/net/bluetooth/af_bluetooth.c @@ -340,6 +340,16 @@ struct sock *bt_accept_dequeue(struct sock *parent, struct socket *newsock) if (newsock) sock_graft(sk, newsock); + /* Hand the caller a reference taken while sk is + * still locked. bt_accept_unlink() just dropped + * the accept-queue reference; without this hold a + * concurrent teardown (e.g. l2cap_conn_del() -> + * l2cap_sock_kill()) could free sk between + * release_sock() and the caller using it. Every + * caller drops this with sock_put() when done. + */ + sock_hold(sk); + release_sock(sk); if (next) sock_put(next); diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c index b971281f0a2b..d7af617cda45 100644 --- a/net/bluetooth/iso.c +++ b/net/bluetooth/iso.c @@ -751,6 +751,8 @@ static void iso_sock_cleanup_listen(struct sock *parent) while ((sk = bt_accept_dequeue(parent, NULL))) { iso_sock_close(sk); iso_sock_kill(sk); + /* Drop the reference handed back by bt_accept_dequeue(). */ + sock_put(sk); } /* If listening socket has a hcon, properly disconnect it */ @@ -1356,8 +1358,13 @@ static int iso_sock_accept(struct socket *sock, struct socket *newsock, } ch = bt_accept_dequeue(sk, newsock); - if (ch) + if (ch) { + /* Drop the bridging ref from bt_accept_dequeue(); + * the grafted socket keeps ch alive from here. + */ + sock_put(ch); break; + } if (!timeo) { err = -EAGAIN; diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c index cf590a67d364..b34e7da8d906 100644 --- a/net/bluetooth/l2cap_sock.c +++ b/net/bluetooth/l2cap_sock.c @@ -349,8 +349,13 @@ static int l2cap_sock_accept(struct socket *sock, struct socket *newsock, } nsk = bt_accept_dequeue(sk, newsock); - if (nsk) + if (nsk) { + /* Drop the bridging ref from bt_accept_dequeue(); + * the grafted socket keeps nsk alive from here. + */ + sock_put(nsk); break; + } if (!timeo) { err = -EAGAIN; @@ -1475,22 +1480,54 @@ static void l2cap_sock_cleanup_listen(struct sock *parent) BT_DBG("parent %p state %s", parent, state_to_string(parent->sk_state)); - /* Close not yet accepted channels */ + /* Close not yet accepted channels. + * + * bt_accept_dequeue() now returns sk with an extra reference held + * (taken while sk was still locked) so a concurrent l2cap_conn_del() + * -> l2cap_sock_kill() cannot free sk under us. + * + * cleanup_listen() runs under the parent sk lock, so unlike + * l2cap_sock_shutdown() we must NOT take conn->lock here: that would + * establish sk_lock -> conn->lock and invert the established + * conn->lock -> chan->lock -> sk_lock order (lockdep deadlock). + * + * Instead, briefly take the child sk lock to fetch and pin its chan. + * l2cap_conn_del() reaches the chan free only via + * l2cap_chan_del() -> l2cap_sock_teardown_cb(), which itself takes + * the child sk lock; holding it across l2cap_chan_hold_unless_zero() + * therefore guarantees the chan cannot be freed while we read and + * pin it (hold_unless_zero() additionally skips a chan already past + * its last reference). We then drop the sk lock before taking + * chan->lock, so sk and chan locks are never held together. + */ while ((sk = bt_accept_dequeue(parent, NULL))) { - struct l2cap_chan *chan = l2cap_pi(sk)->chan; + struct l2cap_chan *chan; + + lock_sock_nested(sk, L2CAP_NESTING_NORMAL); + chan = l2cap_chan_hold_unless_zero(l2cap_pi(sk)->chan); + release_sock(sk); + if (!chan) { + /* l2cap_conn_del() already tearing this child down */ + sock_put(sk); + continue; + } BT_DBG("child chan %p state %s", chan, state_to_string(chan->state)); - l2cap_chan_hold(chan); l2cap_chan_lock(chan); - __clear_chan_timer(chan); l2cap_chan_close(chan, ECONNRESET); - l2cap_sock_kill(sk); - + /* l2cap_conn_del() may already have killed this socket + * (it sets SOCK_DEAD); skip the duplicate to avoid a + * double sock_put()/l2cap_chan_put(). + */ + if (!sock_flag(sk, SOCK_DEAD)) + l2cap_sock_kill(sk); l2cap_chan_unlock(chan); + l2cap_chan_put(chan); + sock_put(sk); } } diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c index be6639cd6f59..bd7d959c6e9e 100644 --- a/net/bluetooth/rfcomm/sock.c +++ b/net/bluetooth/rfcomm/sock.c @@ -180,6 +180,8 @@ static void rfcomm_sock_cleanup_listen(struct sock *parent) while ((sk = bt_accept_dequeue(parent, NULL))) { rfcomm_sock_close(sk); rfcomm_sock_kill(sk); + /* Drop the reference handed back by bt_accept_dequeue(). */ + sock_put(sk); } parent->sk_state = BT_CLOSED; @@ -497,8 +499,13 @@ static int rfcomm_sock_accept(struct socket *sock, struct socket *newsock, } nsk = bt_accept_dequeue(sk, newsock); - if (nsk) + if (nsk) { + /* Drop the bridging ref from bt_accept_dequeue(); + * the grafted socket keeps nsk alive from here. + */ + sock_put(nsk); break; + } if (!timeo) { err = -EAGAIN; diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c index eba44525d41d..f1799c6a6f87 100644 --- a/net/bluetooth/sco.c +++ b/net/bluetooth/sco.c @@ -502,6 +502,8 @@ static void sco_sock_cleanup_listen(struct sock *parent) while ((sk = bt_accept_dequeue(parent, NULL))) { sco_sock_close(sk); sco_sock_kill(sk); + /* Drop the reference handed back by bt_accept_dequeue(). */ + sock_put(sk); } parent->sk_state = BT_CLOSED; @@ -765,8 +767,13 @@ static int sco_sock_accept(struct socket *sock, struct socket *newsock, } ch = bt_accept_dequeue(sk, newsock); - if (ch) + if (ch) { + /* Drop the bridging ref from bt_accept_dequeue(); + * the grafted socket keeps ch alive from here. + */ + sock_put(ch); break; + } if (!timeo) { err = -EAGAIN;