CVE-2024-26638

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

nbd: always initialize struct msghdr completely

syzbot complains that msg->msggetinq value can be uninitialized [1]

struct msghdr got many new fields recently, we should always make sure their values is zero by default.

[1] BUG: KMSAN: uninit-value in tcprecvmsg+0x686/0xac0 net/ipv4/tcp.c:2571 tcprecvmsg+0x686/0xac0 net/ipv4/tcp.c:2571 inetrecvmsg+0x131/0x580 net/ipv4/afinet.c:879 sockrecvmsgnosec net/socket.c:1044 [inline] sockrecvmsg+0x12b/0x1e0 net/socket.c:1066 _sockxmit+0x236/0x5c0 drivers/block/nbd.c:538 nbdreadreply drivers/block/nbd.c:732 [inline] recvwork+0x262/0x3100 drivers/block/nbd.c:863 processonework kernel/workqueue.c:2627 [inline] processscheduledworks+0x104e/0x1e70 kernel/workqueue.c:2700 workerthread+0xf45/0x1490 kernel/workqueue.c:2781 kthread+0x3ed/0x540 kernel/kthread.c:388 retfromfork+0x66/0x80 arch/x86/kernel/process.c:147 retfromforkasm+0x11/0x20 arch/x86/entry/entry_64.S:242

Local variable msg created at: _sockxmit+0x4c/0x5c0 drivers/block/nbd.c:513 nbdreadreply drivers/block/nbd.c:732 [inline] recv_work+0x262/0x3100 drivers/block/nbd.c:863

CPU: 1 PID: 7465 Comm: kworker/u5:1 Not tainted 6.7.0-rc7-syzkaller-00041-gf016f7547aee #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023 Workqueue: nbd5-recv recv_work