CVE-2025-68305: Bluetooth: hci_sock: Prevent race in socket write iter and sock bind

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: hcisock: Prevent race in socket write iter and sock bind

There is a potential race condition between sock bind and socket write iter. bind may free the same cmd via mgmtpending before write iter sends the cmd, just as syzbot reported in UAF[1].

Here we use hcidevlock to synchronize the two, thereby avoiding the UAF mentioned in [1].

[1] syzbot reported: BUG: KASAN: slab-use-after-free in mgmtpendingremove+0x3b/0x210 net/bluetooth/mgmtutil.c:316 Read of size 8 at addr ffff888077164818 by task syz.0.17/5989 Call Trace: mgmtpendingremove+0x3b/0x210 net/bluetooth/mgmtutil.c:316 setlinksecurity+0x5c2/0x710 net/bluetooth/mgmt.c:1918 hcimgmtcmd+0x9c9/0xef0 net/bluetooth/hcisock.c:1719 hcisocksendmsg+0x6ca/0xef0 net/bluetooth/hcisock.c:1839 socksendmsgnosec net/socket.c:727 [inline] socksendmsg+0x21c/0x270 net/socket.c:742 sockwriteiter+0x279/0x360 net/socket.c:1195

Allocated by task 5989: mgmtpendingadd+0x35/0x140 net/bluetooth/mgmtutil.c:296 setlinksecurity+0x557/0x710 net/bluetooth/mgmt.c:1910 hcimgmtcmd+0x9c9/0xef0 net/bluetooth/hcisock.c:1719 hcisocksendmsg+0x6ca/0xef0 net/bluetooth/hcisock.c:1839 socksendmsgnosec net/socket.c:727 [inline] socksendmsg+0x21c/0x270 net/socket.c:742 sockwriteiter+0x279/0x360 net/socket.c:1195

Freed by task 5991: mgmtpendingfree net/bluetooth/mgmtutil.c:311 [inline] mgmtpendingforeach+0x30d/0x380 net/bluetooth/mgmtutil.c:257 mgmtindexremoved+0x112/0x2f0 net/bluetooth/mgmt.c:9477 hcisockbind+0xbe9/0x1000 net/bluetooth/hcisock.c:1314