From: Deepanshu Kartikey <kartikey406@gmail.com> stable inclusion from stable-v6.6.134 commit b256d055da47258e63f8b40965f276c5f23d229a category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/14582 CVE: CVE-2026-43050 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 922814879542c2e397b0e9641fd36b8202a8e555 ] A race condition exists between lec_atm_close() setting priv->lecd to NULL and concurrent access to priv->lecd in send_to_lecd(), lec_handle_bridge(), and lec_atm_send(). When the socket is freed via RCU while another thread is still using it, a use-after-free occurs in sock_def_readable() when accessing the socket's wait queue. The root cause is that lec_atm_close() clears priv->lecd without any synchronization, while callers dereference priv->lecd without any protection against concurrent teardown. Fix this by converting priv->lecd to an RCU-protected pointer: - Mark priv->lecd as __rcu in lec.h - Use rcu_assign_pointer() in lec_atm_close() and lecd_attach() for safe pointer assignment - Use rcu_access_pointer() for NULL checks that do not dereference the pointer in lec_start_xmit(), lec_push(), send_to_lecd() and lecd_attach() - Use rcu_read_lock/rcu_dereference/rcu_read_unlock in send_to_lecd(), lec_handle_bridge() and lec_atm_send() to safely access lecd - Use rcu_assign_pointer() followed by synchronize_rcu() in lec_atm_close() to ensure all readers have completed before proceeding. This is safe since lec_atm_close() is called from vcc_release() which holds lock_sock(), a sleeping lock. - Remove the manual sk_receive_queue drain from lec_atm_close() since vcc_destroy_socket() already drains it after lec_atm_close() returns. v2: Switch from spinlock + sock_hold/put approach to RCU to properly fix the race. The v1 spinlock approach had two issues pointed out by Eric Dumazet: 1. priv->lecd was still accessed directly after releasing the lock instead of using a local copy. 2. The spinlock did not prevent packets being queued after lec_atm_close() drains sk_receive_queue since timer and workqueue paths bypass netif_stop_queue(). Note: Syzbot patch testing was attempted but the test VM terminated unexpectedly with "Connection to localhost closed by remote host", likely due to a QEMU AHCI emulation issue unrelated to this fix. Compile testing with "make W=1 net/atm/lec.o" passes cleanly. Reported-by: syzbot+f50072212ab792c86925@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=f50072212ab792c86925 Link: https://lore.kernel.org/all/20260309093614.502094-1-kartikey406@gmail.com/T/ [v1] Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20260309155908.508768-1-kartikey406@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Yi Yang <yiyang13@huawei.com> --- net/atm/lec.c | 72 +++++++++++++++++++++++++++++++++------------------ net/atm/lec.h | 2 +- 2 files changed, 48 insertions(+), 26 deletions(-) diff --git a/net/atm/lec.c b/net/atm/lec.c index b7fa48a9b720..e14b7ca8b17e 100644 --- a/net/atm/lec.c +++ b/net/atm/lec.c @@ -154,10 +154,19 @@ static void lec_handle_bridge(struct sk_buff *skb, struct net_device *dev) /* 0x01 is topology change */ priv = netdev_priv(dev); - atm_force_charge(priv->lecd, skb2->truesize); - sk = sk_atm(priv->lecd); - skb_queue_tail(&sk->sk_receive_queue, skb2); - sk->sk_data_ready(sk); + struct atm_vcc *vcc; + + rcu_read_lock(); + vcc = rcu_dereference(priv->lecd); + if (vcc) { + atm_force_charge(vcc, skb2->truesize); + sk = sk_atm(vcc); + skb_queue_tail(&sk->sk_receive_queue, skb2); + sk->sk_data_ready(sk); + } else { + dev_kfree_skb(skb2); + } + rcu_read_unlock(); } } #endif /* IS_ENABLED(CONFIG_BRIDGE) */ @@ -216,7 +225,7 @@ static netdev_tx_t lec_start_xmit(struct sk_buff *skb, int is_rdesc; pr_debug("called\n"); - if (!priv->lecd) { + if (!rcu_access_pointer(priv->lecd)) { pr_info("%s:No lecd attached\n", dev->name); dev->stats.tx_errors++; netif_stop_queue(dev); @@ -449,10 +458,19 @@ static int lec_atm_send(struct atm_vcc *vcc, struct sk_buff *skb) break; skb2->len = sizeof(struct atmlec_msg); skb_copy_to_linear_data(skb2, mesg, sizeof(*mesg)); - atm_force_charge(priv->lecd, skb2->truesize); - sk = sk_atm(priv->lecd); - skb_queue_tail(&sk->sk_receive_queue, skb2); - sk->sk_data_ready(sk); + struct atm_vcc *vcc; + + rcu_read_lock(); + vcc = rcu_dereference(priv->lecd); + if (vcc) { + atm_force_charge(vcc, skb2->truesize); + sk = sk_atm(vcc); + skb_queue_tail(&sk->sk_receive_queue, skb2); + sk->sk_data_ready(sk); + } else { + dev_kfree_skb(skb2); + } + rcu_read_unlock(); } } #endif /* IS_ENABLED(CONFIG_BRIDGE) */ @@ -468,23 +486,16 @@ static int lec_atm_send(struct atm_vcc *vcc, struct sk_buff *skb) static void lec_atm_close(struct atm_vcc *vcc) { - struct sk_buff *skb; struct net_device *dev = (struct net_device *)vcc->proto_data; struct lec_priv *priv = netdev_priv(dev); - priv->lecd = NULL; + rcu_assign_pointer(priv->lecd, NULL); + synchronize_rcu(); /* Do something needful? */ netif_stop_queue(dev); lec_arp_destroy(priv); - if (skb_peek(&sk_atm(vcc)->sk_receive_queue)) - pr_info("%s closing with messages pending\n", dev->name); - while ((skb = skb_dequeue(&sk_atm(vcc)->sk_receive_queue))) { - atm_return(vcc, skb->truesize); - dev_kfree_skb(skb); - } - pr_info("%s: Shut down!\n", dev->name); module_put(THIS_MODULE); } @@ -510,12 +521,14 @@ send_to_lecd(struct lec_priv *priv, atmlec_msg_type type, const unsigned char *mac_addr, const unsigned char *atm_addr, struct sk_buff *data) { + struct atm_vcc *vcc; struct sock *sk; struct sk_buff *skb; struct atmlec_msg *mesg; - if (!priv || !priv->lecd) + if (!priv || !rcu_access_pointer(priv->lecd)) return -1; + skb = alloc_skb(sizeof(struct atmlec_msg), GFP_ATOMIC); if (!skb) return -1; @@ -532,18 +545,27 @@ send_to_lecd(struct lec_priv *priv, atmlec_msg_type type, if (atm_addr) memcpy(&mesg->content.normal.atm_addr, atm_addr, ATM_ESA_LEN); - atm_force_charge(priv->lecd, skb->truesize); - sk = sk_atm(priv->lecd); + rcu_read_lock(); + vcc = rcu_dereference(priv->lecd); + if (!vcc) { + rcu_read_unlock(); + kfree_skb(skb); + return -1; + } + + atm_force_charge(vcc, skb->truesize); + sk = sk_atm(vcc); skb_queue_tail(&sk->sk_receive_queue, skb); sk->sk_data_ready(sk); if (data != NULL) { pr_debug("about to send %d bytes of data\n", data->len); - atm_force_charge(priv->lecd, data->truesize); + atm_force_charge(vcc, data->truesize); skb_queue_tail(&sk->sk_receive_queue, data); sk->sk_data_ready(sk); } + rcu_read_unlock(); return 0; } @@ -618,7 +640,7 @@ static void lec_push(struct atm_vcc *vcc, struct sk_buff *skb) atm_return(vcc, skb->truesize); if (*(__be16 *) skb->data == htons(priv->lecid) || - !priv->lecd || !(dev->flags & IFF_UP)) { + !rcu_access_pointer(priv->lecd) || !(dev->flags & IFF_UP)) { /* * Probably looping back, or if lecd is missing, * lecd has gone down @@ -753,12 +775,12 @@ static int lecd_attach(struct atm_vcc *vcc, int arg) priv = netdev_priv(dev_lec[i]); } else { priv = netdev_priv(dev_lec[i]); - if (priv->lecd) + if (rcu_access_pointer(priv->lecd)) return -EADDRINUSE; } lec_arp_init(priv); priv->itfnum = i; /* LANE2 addition */ - priv->lecd = vcc; + rcu_assign_pointer(priv->lecd, vcc); vcc->dev = &lecatm_dev; vcc_insert_socket(sk_atm(vcc)); diff --git a/net/atm/lec.h b/net/atm/lec.h index be0e2667bd8c..ec85709bf818 100644 --- a/net/atm/lec.h +++ b/net/atm/lec.h @@ -91,7 +91,7 @@ struct lec_priv { */ spinlock_t lec_arp_lock; struct atm_vcc *mcast_vcc; /* Default Multicast Send VCC */ - struct atm_vcc *lecd; + struct atm_vcc __rcu *lecd; struct delayed_work lec_arp_work; /* C10 */ unsigned int maximum_unknown_frame_count; /* -- 2.25.1