From 042bb9603c44620dce98717a2d23235ca57a00d7 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Danis?= Date: Thu, 12 Jun 2025 09:50:34 +0200 Subject: Bluetooth: L2CAP: Fix L2CAP MTU negotiation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit OBEX download from iPhone is currently slow due to small packet size used to transfer data which doesn't follow the MTU negotiated during L2CAP connection, i.e. 672 bytes instead of 32767: < ACL Data TX: Handle 11 flags 0x00 dlen 12 L2CAP: Connection Request (0x02) ident 18 len 4 PSM: 4103 (0x1007) Source CID: 72 > ACL Data RX: Handle 11 flags 0x02 dlen 16 L2CAP: Connection Response (0x03) ident 18 len 8 Destination CID: 14608 Source CID: 72 Result: Connection successful (0x0000) Status: No further information available (0x0000) < ACL Data TX: Handle 11 flags 0x00 dlen 27 L2CAP: Configure Request (0x04) ident 20 len 19 Destination CID: 14608 Flags: 0x0000 Option: Maximum Transmission Unit (0x01) [mandatory] MTU: 32767 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 63 Max transmit: 3 Retransmission timeout: 2000 Monitor timeout: 12000 Maximum PDU size: 1009 > ACL Data RX: Handle 11 flags 0x02 dlen 26 L2CAP: Configure Request (0x04) ident 72 len 18 Destination CID: 72 Flags: 0x0000 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 32 Max transmit: 255 Retransmission timeout: 0 Monitor timeout: 0 Maximum PDU size: 65527 Option: Frame Check Sequence (0x05) [mandatory] FCS: 16-bit FCS (0x01) < ACL Data TX: Handle 11 flags 0x00 dlen 29 L2CAP: Configure Response (0x05) ident 72 len 21 Source CID: 14608 Flags: 0x0000 Result: Success (0x0000) Option: Maximum Transmission Unit (0x01) [mandatory] MTU: 672 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 32 Max transmit: 255 Retransmission timeout: 2000 Monitor timeout: 12000 Maximum PDU size: 1009 > ACL Data RX: Handle 11 flags 0x02 dlen 32 L2CAP: Configure Response (0x05) ident 20 len 24 Source CID: 72 Flags: 0x0000 Result: Success (0x0000) Option: Maximum Transmission Unit (0x01) [mandatory] MTU: 32767 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 63 Max transmit: 3 Retransmission timeout: 2000 Monitor timeout: 12000 Maximum PDU size: 1009 Option: Frame Check Sequence (0x05) [mandatory] FCS: 16-bit FCS (0x01) ... > ACL Data RX: Handle 11 flags 0x02 dlen 680 Channel: 72 len 676 ctrl 0x0202 [PSM 4103 mode Enhanced Retransmission (0x03)] {chan 8} I-frame: Unsegmented TxSeq 1 ReqSeq 2 < ACL Data TX: Handle 11 flags 0x00 dlen 13 Channel: 14608 len 9 ctrl 0x0204 [PSM 4103 mode Enhanced Retransmission (0x03)] {chan 8} I-frame: Unsegmented TxSeq 2 ReqSeq 2 > ACL Data RX: Handle 11 flags 0x02 dlen 680 Channel: 72 len 676 ctrl 0x0304 [PSM 4103 mode Enhanced Retransmission (0x03)] {chan 8} I-frame: Unsegmented TxSeq 2 ReqSeq 3 The MTUs are negotiated for each direction. In this traces 32767 for iPhone->localhost and no MTU for localhost->iPhone, which based on '4.4 L2CAP_CONFIGURATION_REQ' (Core specification v5.4, Vol. 3, Part A): The only parameters that should be included in the L2CAP_CONFIGURATION_REQ packet are those that require different values than the default or previously agreed values. ... Any missing configuration parameters are assumed to have their most recently explicitly or implicitly accepted values. and '5.1 Maximum transmission unit (MTU)': If the remote device sends a positive L2CAP_CONFIGURATION_RSP packet it should include the actual MTU to be used on this channel for traffic flowing into the local device. ... The default value is 672 octets. is set by BlueZ to 672 bytes. It seems that the iPhone used the lowest negotiated value to transfer data to the localhost instead of the negotiated one for the incoming direction. This could be fixed by using the MTU negotiated for the other direction, if exists, in the L2CAP_CONFIGURATION_RSP. This allows to use segmented packets as in the following traces: < ACL Data TX: Handle 11 flags 0x00 dlen 12 L2CAP: Connection Request (0x02) ident 22 len 4 PSM: 4103 (0x1007) Source CID: 72 < ACL Data TX: Handle 11 flags 0x00 dlen 27 L2CAP: Configure Request (0x04) ident 24 len 19 Destination CID: 2832 Flags: 0x0000 Option: Maximum Transmission Unit (0x01) [mandatory] MTU: 32767 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 63 Max transmit: 3 Retransmission timeout: 2000 Monitor timeout: 12000 Maximum PDU size: 1009 > ACL Data RX: Handle 11 flags 0x02 dlen 26 L2CAP: Configure Request (0x04) ident 15 len 18 Destination CID: 72 Flags: 0x0000 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 32 Max transmit: 255 Retransmission timeout: 0 Monitor timeout: 0 Maximum PDU size: 65527 Option: Frame Check Sequence (0x05) [mandatory] FCS: 16-bit FCS (0x01) < ACL Data TX: Handle 11 flags 0x00 dlen 29 L2CAP: Configure Response (0x05) ident 15 len 21 Source CID: 2832 Flags: 0x0000 Result: Success (0x0000) Option: Maximum Transmission Unit (0x01) [mandatory] MTU: 32767 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 32 Max transmit: 255 Retransmission timeout: 2000 Monitor timeout: 12000 Maximum PDU size: 1009 > ACL Data RX: Handle 11 flags 0x02 dlen 32 L2CAP: Configure Response (0x05) ident 24 len 24 Source CID: 72 Flags: 0x0000 Result: Success (0x0000) Option: Maximum Transmission Unit (0x01) [mandatory] MTU: 32767 Option: Retransmission and Flow Control (0x04) [mandatory] Mode: Enhanced Retransmission (0x03) TX window size: 63 Max transmit: 3 Retransmission timeout: 2000 Monitor timeout: 12000 Maximum PDU size: 1009 Option: Frame Check Sequence (0x05) [mandatory] FCS: 16-bit FCS (0x01) ... > ACL Data RX: Handle 11 flags 0x02 dlen 1009 Channel: 72 len 1005 ctrl 0x4202 [PSM 4103 mode Enhanced Retransmission (0x03)] {chan 8} I-frame: Start (len 21884) TxSeq 1 ReqSeq 2 > ACL Data RX: Handle 11 flags 0x02 dlen 1009 Channel: 72 len 1005 ctrl 0xc204 [PSM 4103 mode Enhanced Retransmission (0x03)] {chan 8} I-frame: Continuation TxSeq 2 ReqSeq 2 This has been tested with kernel 5.4 and BlueZ 5.77. Cc: stable@vger.kernel.org Signed-off-by: Frédéric Danis Signed-off-by: Luiz Augusto von Dentz --- net/bluetooth/l2cap_core.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'net/bluetooth') diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index a5bde5db58ef..40daa38276f3 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -3415,7 +3415,7 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data struct l2cap_conf_rfc rfc = { .mode = L2CAP_MODE_BASIC }; struct l2cap_conf_efs efs; u8 remote_efs = 0; - u16 mtu = L2CAP_DEFAULT_MTU; + u16 mtu = 0; u16 result = L2CAP_CONF_SUCCESS; u16 size; @@ -3520,6 +3520,13 @@ done: /* Configure output options and let the other side know * which ones we don't like. */ + /* If MTU is not provided in configure request, use the most recently + * explicitly or implicitly accepted value for the other direction, + * or the default value. + */ + if (mtu == 0) + mtu = chan->imtu ? chan->imtu : L2CAP_DEFAULT_MTU; + if (mtu < L2CAP_DEFAULT_MIN_MTU) result = L2CAP_CONF_UNACCEPT; else { -- cgit v1.2.3 From 1d6123102e9fbedc8d25bf4731da6d513173e49e Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Tue, 17 Jun 2025 09:58:13 -0700 Subject: Bluetooth: hci_core: Fix use-after-free in vhci_flush() syzbot reported use-after-free in vhci_flush() without repro. [0] From the splat, a thread close()d a vhci file descriptor while its device was being used by iotcl() on another thread. Once the last fd refcnt is released, vhci_release() calls hci_unregister_dev(), hci_free_dev(), and kfree() for struct vhci_data, which is set to hci_dev->dev->driver_data. The problem is that there is no synchronisation after unlinking hdev from hci_dev_list in hci_unregister_dev(). There might be another thread still accessing the hdev which was fetched before the unlink operation. We can use SRCU for such synchronisation. Let's run hci_dev_reset() under SRCU and wait for its completion in hci_unregister_dev(). Another option would be to restore hci_dev->destruct(), which was removed in commit 587ae086f6e4 ("Bluetooth: Remove unused hci-destruct cb"). However, this would not be a good solution, as we should not run hci_unregister_dev() while there are in-flight ioctl() requests, which could lead to another data-race KCSAN splat. Note that other drivers seem to have the same problem, for exmaple, virtbt_remove(). [0]: BUG: KASAN: slab-use-after-free in skb_queue_empty_lockless include/linux/skbuff.h:1891 [inline] BUG: KASAN: slab-use-after-free in skb_queue_purge_reason+0x99/0x360 net/core/skbuff.c:3937 Read of size 8 at addr ffff88807cb8d858 by task syz.1.219/6718 CPU: 1 UID: 0 PID: 6718 Comm: syz.1.219 Not tainted 6.16.0-rc1-syzkaller-00196-g08207f42d3ff #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0xd2/0x2b0 mm/kasan/report.c:521 kasan_report+0x118/0x150 mm/kasan/report.c:634 skb_queue_empty_lockless include/linux/skbuff.h:1891 [inline] skb_queue_purge_reason+0x99/0x360 net/core/skbuff.c:3937 skb_queue_purge include/linux/skbuff.h:3368 [inline] vhci_flush+0x44/0x50 drivers/bluetooth/hci_vhci.c:69 hci_dev_do_reset net/bluetooth/hci_core.c:552 [inline] hci_dev_reset+0x420/0x5c0 net/bluetooth/hci_core.c:592 sock_do_ioctl+0xd9/0x300 net/socket.c:1190 sock_ioctl+0x576/0x790 net/socket.c:1311 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fcf5b98e929 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fcf5c7b9038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00007fcf5bbb6160 RCX: 00007fcf5b98e929 RDX: 0000000000000000 RSI: 00000000400448cb RDI: 0000000000000009 RBP: 00007fcf5ba10b39 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007fcf5bbb6160 R15: 00007ffd6353d528 Allocated by task 6535: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:377 [inline] __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394 kasan_kmalloc include/linux/kasan.h:260 [inline] __kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4359 kmalloc_noprof include/linux/slab.h:905 [inline] kzalloc_noprof include/linux/slab.h:1039 [inline] vhci_open+0x57/0x360 drivers/bluetooth/hci_vhci.c:635 misc_open+0x2bc/0x330 drivers/char/misc.c:161 chrdev_open+0x4c9/0x5e0 fs/char_dev.c:414 do_dentry_open+0xdf0/0x1970 fs/open.c:964 vfs_open+0x3b/0x340 fs/open.c:1094 do_open fs/namei.c:3887 [inline] path_openat+0x2ee5/0x3830 fs/namei.c:4046 do_filp_open+0x1fa/0x410 fs/namei.c:4073 do_sys_openat2+0x121/0x1c0 fs/open.c:1437 do_sys_open fs/open.c:1452 [inline] __do_sys_openat fs/open.c:1468 [inline] __se_sys_openat fs/open.c:1463 [inline] __x64_sys_openat+0x138/0x170 fs/open.c:1463 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f Freed by task 6535: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:68 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576 poison_slab_object mm/kasan/common.c:247 [inline] __kasan_slab_free+0x62/0x70 mm/kasan/common.c:264 kasan_slab_free include/linux/kasan.h:233 [inline] slab_free_hook mm/slub.c:2381 [inline] slab_free mm/slub.c:4643 [inline] kfree+0x18e/0x440 mm/slub.c:4842 vhci_release+0xbc/0xd0 drivers/bluetooth/hci_vhci.c:671 __fput+0x44c/0xa70 fs/file_table.c:465 task_work_run+0x1d1/0x260 kernel/task_work.c:227 exit_task_work include/linux/task_work.h:40 [inline] do_exit+0x6ad/0x22e0 kernel/exit.c:955 do_group_exit+0x21c/0x2d0 kernel/exit.c:1104 __do_sys_exit_group kernel/exit.c:1115 [inline] __se_sys_exit_group kernel/exit.c:1113 [inline] __x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1113 x64_sys_call+0x21ba/0x21c0 arch/x86/include/generated/asm/syscalls_64.h:232 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f The buggy address belongs to the object at ffff88807cb8d800 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 88 bytes inside of freed 1024-byte region [ffff88807cb8d800, ffff88807cb8dc00) Fixes: bf18c7118cf8 ("Bluetooth: vhci: Free driver_data on file release") Reported-by: syzbot+2faa4825e556199361f9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=f62d64848fc4c7c30cd6 Signed-off-by: Kuniyuki Iwashima Acked-by: Paul Menzel Signed-off-by: Luiz Augusto von Dentz --- net/bluetooth/hci_core.c | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-) (limited to 'net/bluetooth') diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c index 07a8b4281a39..14d7221b8ac0 100644 --- a/net/bluetooth/hci_core.c +++ b/net/bluetooth/hci_core.c @@ -64,7 +64,7 @@ static DEFINE_IDA(hci_index_ida); /* Get HCI device by index. * Device is held on return. */ -struct hci_dev *hci_dev_get(int index) +static struct hci_dev *__hci_dev_get(int index, int *srcu_index) { struct hci_dev *hdev = NULL, *d; @@ -77,6 +77,8 @@ struct hci_dev *hci_dev_get(int index) list_for_each_entry(d, &hci_dev_list, list) { if (d->id == index) { hdev = hci_dev_hold(d); + if (srcu_index) + *srcu_index = srcu_read_lock(&d->srcu); break; } } @@ -84,6 +86,22 @@ struct hci_dev *hci_dev_get(int index) return hdev; } +struct hci_dev *hci_dev_get(int index) +{ + return __hci_dev_get(index, NULL); +} + +static struct hci_dev *hci_dev_get_srcu(int index, int *srcu_index) +{ + return __hci_dev_get(index, srcu_index); +} + +static void hci_dev_put_srcu(struct hci_dev *hdev, int srcu_index) +{ + srcu_read_unlock(&hdev->srcu, srcu_index); + hci_dev_put(hdev); +} + /* ---- Inquiry support ---- */ bool hci_discovery_active(struct hci_dev *hdev) @@ -568,9 +586,9 @@ static int hci_dev_do_reset(struct hci_dev *hdev) int hci_dev_reset(__u16 dev) { struct hci_dev *hdev; - int err; + int err, srcu_index; - hdev = hci_dev_get(dev); + hdev = hci_dev_get_srcu(dev, &srcu_index); if (!hdev) return -ENODEV; @@ -592,7 +610,7 @@ int hci_dev_reset(__u16 dev) err = hci_dev_do_reset(hdev); done: - hci_dev_put(hdev); + hci_dev_put_srcu(hdev, srcu_index); return err; } @@ -2433,6 +2451,11 @@ struct hci_dev *hci_alloc_dev_priv(int sizeof_priv) if (!hdev) return NULL; + if (init_srcu_struct(&hdev->srcu)) { + kfree(hdev); + return NULL; + } + hdev->pkt_type = (HCI_DM1 | HCI_DH1 | HCI_HV1); hdev->esco_type = (ESCO_HV1); hdev->link_mode = (HCI_LM_ACCEPT); @@ -2678,6 +2701,9 @@ void hci_unregister_dev(struct hci_dev *hdev) list_del(&hdev->list); write_unlock(&hci_dev_list_lock); + synchronize_srcu(&hdev->srcu); + cleanup_srcu_struct(&hdev->srcu); + disable_work_sync(&hdev->rx_work); disable_work_sync(&hdev->cmd_work); disable_work_sync(&hdev->tx_work); -- cgit v1.2.3