Extend a critical section to prevent chan from early freeing. Also make the l2cap_connect() return type void. Nothing is using the returned value but it is ugly to return a potentially freed pointer. Making it void will help with backports because earlier kernels did use the return value. Now the compile will break for kernels where this patch is not a complete fix. The patch is copied from https://gist.github.com/Vudentz/c0c09ca0eff64a32ca50b1a6eb41295d Thank you for your help, Dan and Luiz. Call stack summary: [use] l2cap_bredr_sig_cmd l2cap_connect ┌ mutex_lock(&conn->chan_lock); │ chan = pchan->ops->new_connection(pchan); <- alloc chan │ __l2cap_chan_add(conn, chan); │ l2cap_chan_hold(chan); │ list_add(&chan->list, &conn->chan_l); ... (1) └ mutex_unlock(&conn->chan_lock); chan->conf_state ... (4) <- use after free [free] l2cap_conn_del ┌ mutex_lock(&conn->chan_lock); │ foreach chan in conn->chan_l: ... (2) │ l2cap_chan_put(chan); │ l2cap_chan_destroy │ kfree(chan) ... (3) <- chan freed └ mutex_unlock(&conn->chan_lock); ================================================================== BUG: KASAN: slab-use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline] BUG: KASAN: slab-use-after-free in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline] BUG: KASAN: slab-use-after-free in l2cap_connect+0xa67/0x11a0 net/bluetooth/l2cap_core.c:4260 Read of size 8 at addr ffff88810bf040a0 by task kworker/u3:1/311 CPU: 0 PID: 311 Comm: kworker/u3:1 Not tainted 6.8.0+ #61 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 Workqueue: hci0 hci_rx_work Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x85/0xb0 lib/dump_stack.c:106 print_address_description mm/kasan/report.c:377 [inline] print_report+0x18f/0x560 mm/kasan/report.c:488 kasan_report+0xd7/0x110 mm/kasan/report.c:601 kasan_check_range+0x262/0x2f0 mm/kasan/generic.c:189 __kasan_check_read+0x15/0x20 mm/kasan/shadow.c:31 instrument_atomic_read include/linux/instrumented.h:68 [inline] _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline] l2cap_connect+0xa67/0x11a0 net/bluetooth/l2cap_core.c:4260 l2cap_bredr_sig_cmd+0x17fe/0x9a70 l2cap_sig_channel net/bluetooth/l2cap_core.c:6539 [inline] l2cap_recv_frame+0x82e/0x86a0 net/bluetooth/l2cap_core.c:7818 l2cap_recv_acldata+0x379/0xbe0 net/bluetooth/l2cap_core.c:8536 hci_acldata_packet net/bluetooth/hci_core.c:3876 [inline] hci_rx_work+0x64b/0xcb0 net/bluetooth/hci_core.c:4111 process_one_work kernel/workqueue.c:2633 [inline] process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706 worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787 kthread+0x2a9/0x340 kernel/kthread.c:388 ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243 </TASK> Allocated by task 311: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x30/0x70 mm/kasan/common.c:68 kasan_save_alloc_info+0x3c/0x50 mm/kasan/generic.c:575 poison_kmalloc_redzone mm/kasan/common.c:370 [inline] __kasan_kmalloc+0xa2/0xc0 mm/kasan/common.c:387 kasan_kmalloc include/linux/kasan.h:211 [inline] kmalloc_trace+0x1c9/0x390 mm/slub.c:4012 kmalloc include/linux/slab.h:590 [inline] kzalloc include/linux/slab.h:711 [inline] l2cap_chan_create+0x59/0xc80 net/bluetooth/l2cap_core.c:466 l2cap_sock_alloc net/bluetooth/l2cap_sock.c:1849 [inline] l2cap_sock_new_connection_cb+0x14d/0x2a0 net/bluetooth/l2cap_sock.c:1457 l2cap_connect+0x329/0x11a0 net/bluetooth/l2cap_core.c:4176 l2cap_bredr_sig_cmd+0x17fe/0x9a70 l2cap_sig_channel net/bluetooth/l2cap_core.c:6539 [inline] l2cap_recv_frame+0x82e/0x86a0 net/bluetooth/l2cap_core.c:7818 l2cap_recv_acldata+0x379/0xbe0 net/bluetooth/l2cap_core.c:8536 hci_acldata_packet net/bluetooth/hci_core.c:3876 [inline] hci_rx_work+0x64b/0xcb0 net/bluetooth/hci_core.c:4111 process_one_work kernel/workqueue.c:2633 [inline] process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706 worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787 kthread+0x2a9/0x340 kernel/kthread.c:388 ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243 Freed by task 66: kasan_save_stack mm/kasan/common.c:47 [inline] kasan_save_track+0x30/0x70 mm/kasan/common.c:68 kasan_save_free_info+0x44/0x50 mm/kasan/generic.c:589 poison_slab_object+0x11a/0x190 mm/kasan/common.c:240 __kasan_slab_free+0x3b/0x60 mm/kasan/common.c:256 kasan_slab_free include/linux/kasan.h:184 [inline] slab_free_hook mm/slub.c:2121 [inline] slab_free mm/slub.c:4299 [inline] kfree+0x106/0x2e0 mm/slub.c:4409 l2cap_chan_destroy net/bluetooth/l2cap_core.c:509 [inline] kref_put include/linux/kref.h:65 [inline] l2cap_chan_put+0x1e7/0x2b0 net/bluetooth/l2cap_core.c:533 l2cap_conn_del+0x38e/0x5f0 net/bluetooth/l2cap_core.c:1929 l2cap_connect_cfm+0xc2/0x11e0 net/bluetooth/l2cap_core.c:8254 hci_connect_cfm include/net/bluetooth/hci_core.h:1986 [inline] hci_conn_failed+0x202/0x370 net/bluetooth/hci_conn.c:1289 hci_abort_conn_sync+0x913/0xae0 net/bluetooth/hci_sync.c:5359 abort_conn_sync+0xda/0x110 net/bluetooth/hci_conn.c:2988 hci_cmd_sync_work+0x20d/0x3e0 net/bluetooth/hci_sync.c:306 process_one_work kernel/workqueue.c:2633 [inline] process_scheduled_works+0x6b9/0xdc0 kernel/workqueue.c:2706 worker_thread+0xb2b/0x13d0 kernel/workqueue.c:2787 kthread+0x2a9/0x340 kernel/kthread.c:388 ret_from_fork+0x5c/0x90 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1b/0x30 arch/x86/entry/entry_64.S:243 The buggy address belongs to the object at ffff88810bf04000 which belongs to the cache kmalloc-1k of size 1024 The buggy address is located 160 bytes inside of freed 1024-byte region [ffff88810bf04000, ffff88810bf04400) The buggy address belongs to the physical page: page:00000000567b7faa refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10bf04 head:00000000567b7faa order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0 anon flags: 0x17ffffc0000840(slab|head|node=0|zone=2|lastcpupid=0x1fffff) page_type: 0xffffffff() raw: 0017ffffc0000840 ffff888100041dc0 0000000000000000 0000000000000001 raw: 0000000000000000 0000000080080008 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff88810bf03f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88810bf04000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb >ffff88810bf04080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff88810bf04100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff88810bf04180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== Fixes: 73ffa904b782 ("Bluetooth: Move conf_{req,rsp} stuff to struct l2cap_chan") Signed-off-by: Sungwoo Kim <iam@xxxxxxxxxxxx> --- V1 -> V2: Make l2cap_connect() return void. Fix a wrong stack trace attached. V2 -> V3: Extend a lock instead of additional hold and lock net/bluetooth/l2cap_core.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 84fc70862..eeba16f69 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -3902,13 +3902,13 @@ static inline int l2cap_command_rej(struct l2cap_conn *conn, return 0; } -static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn, +static void l2cap_connect(struct l2cap_conn *conn, struct l2cap_cmd_hdr *cmd, u8 *data, u8 rsp_code, u8 amp_id) { struct l2cap_conn_req *req = (struct l2cap_conn_req *) data; struct l2cap_conn_rsp rsp; - struct l2cap_chan *chan = NULL, *pchan; + struct l2cap_chan *chan = NULL, *pchan = NULL; int result, status = L2CAP_CS_NO_INFO; u16 dcid = 0, scid = __le16_to_cpu(req->scid); @@ -3921,7 +3921,7 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn, &conn->hcon->dst, ACL_LINK); if (!pchan) { result = L2CAP_CR_BAD_PSM; - goto sendresp; + goto response; } mutex_lock(&conn->chan_lock); @@ -4008,17 +4008,15 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn, } response: - l2cap_chan_unlock(pchan); - mutex_unlock(&conn->chan_lock); - l2cap_chan_put(pchan); - -sendresp: rsp.scid = cpu_to_le16(scid); rsp.dcid = cpu_to_le16(dcid); rsp.result = cpu_to_le16(result); rsp.status = cpu_to_le16(status); l2cap_send_cmd(conn, cmd->ident, rsp_code, sizeof(rsp), &rsp); + if (!pchan) + return; + if (result == L2CAP_CR_PEND && status == L2CAP_CS_NO_INFO) { struct l2cap_info_req info; info.type = cpu_to_le16(L2CAP_IT_FEAT_MASK); @@ -4041,7 +4039,9 @@ static struct l2cap_chan *l2cap_connect(struct l2cap_conn *conn, chan->num_conf_req++; } - return chan; + l2cap_chan_unlock(pchan); + mutex_unlock(&conn->chan_lock); + l2cap_chan_put(pchan); } static int l2cap_connect_req(struct l2cap_conn *conn, -- 2.34.1
