CVE-2022-50531: tipc: fix an information leak in tipc_topsrv_kern_subscr

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

tipc: fix an information leak in tipctopsrvkernsubscr

Use a 8-byte write to initialize sub.usrhandle in tipctopsrvkernsubscr(), otherwise four bytes remain uninitialized when issuing setsockopt(..., SOLTIPC, ...). This resulted in an infoleak reported by KMSAN when the packet was received:

===================================================== BUG: KMSAN: kernel-infoleak in copyout+0xbc/0x100 lib/ioviter.c:169 instrumentcopytouser ./include/linux/instrumented.h:121 copyout+0xbc/0x100 lib/ioviter.c:169 copytoiter+0x5c0/0x20a0 lib/ioviter.c:527 copytoiter ./include/linux/uio.h:176 simplecopytoiter+0x64/0xa0 net/core/datagram.c:513 skbdatagramiter+0x123/0xdc0 net/core/datagram.c:419 skbcopydatagramiter+0x58/0x200 net/core/datagram.c:527 skbcopydatagrammsg ./include/linux/skbuff.h:3903 packetrecvmsg+0x521/0x1e70 net/packet/afpacket.c:3469 sysrecvmsg+0x2c4/0x810 net/socket.c:? sysrecvmsg+0x217/0x840 net/socket.c:2743 sysrecvmsg net/socket.c:2773 dosysrecvmsg net/socket.c:2783 sesysrecvmsg net/socket.c:2780 x64sysrecvmsg+0x364/0x540 net/socket.c:2780 dosyscallx64 arch/x86/entry/common.c:50 dosyscall64+0x3d/0xb0 arch/x86/entry/common.c:80 entrySYSCALL64afterhwframe+0x63/0xcd arch/x86/entry/entry64.S:120

...

Uninit was stored to memory at: tipcsubsubscribe+0x42d/0xb50 net/tipc/subscr.c:156 tipcconnrcvsub+0x246/0x620 net/tipc/topsrv.c:375 tipctopsrvkernsubscr+0x2e8/0x400 net/tipc/topsrv.c:579 tipcgroupcreate+0x4e7/0x7d0 net/tipc/group.c:190 tipcskjoin+0x2a8/0x770 net/tipc/socket.c:3084 tipcsetsockopt+0xae5/0xe40 net/tipc/socket.c:3201 syssetsockopt+0x87f/0xdc0 net/socket.c:2252 dosyssetsockopt net/socket.c:2263 sesyssetsockopt net/socket.c:2260 x64syssetsockopt+0xe0/0x160 net/socket.c:2260 dosyscallx64 arch/x86/entry/common.c:50 dosyscall64+0x3d/0xb0 arch/x86/entry/common.c:80 entrySYSCALL64afterhwframe+0x63/0xcd arch/x86/entry/entry64.S:120

Local variable sub created at: tipctopsrvkernsubscr+0x57/0x400 net/tipc/topsrv.c:562 tipcgroupcreate+0x4e7/0x7d0 net/tipc/group.c:190

Bytes 84-87 of 88 are uninitialized Memory access of size 88 starts at ffff88801ed57cd0 Data copied to user address 0000000020000400 ... =====================================================