CVE-2023-52700: tipc: fix kernel warning when sending SYN message

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

tipc: fix kernel warning when sending SYN message

When sending a SYN message, this kernel stack trace is observed:

... [ 13.396352] RIP: 0010:copyfromiter+0xb4/0x550 ... [ 13.398494] Call Trace: [ 13.398630] <TASK> [ 13.398630] ? allocskb+0xed/0x1a0 [ 13.398630] tipcmsgbuild+0x12c/0x670 [tipc] [ 13.398630] ? shmemaddtopagecache.isra.71+0x151/0x290 [ 13.398630] tipcsendmsg+0x2d1/0x710 [tipc] [ 13.398630] ? tipcconnect+0x1d9/0x230 [tipc] [ 13.398630] ? localbhenableip+0x37/0x80 [ 13.398630] tipcconnect+0x1d9/0x230 [tipc] [ 13.398630] ? sysconnect+0x9f/0xd0 [ 13.398630] sysconnect+0x9f/0xd0 [ 13.398630] ? preemptcountadd+0x4d/0xa0 [ 13.398630] ? fpregsassertstateconsistent+0x22/0x50 [ 13.398630] x64sysconnect+0x16/0x20 [ 13.398630] dosyscall64+0x42/0x90 [ 13.398630] entrySYSCALL64afterhwframe+0x63/0xcd

It is because commit a41dad905e5a ("ioviter: saner checks for attempt to copy to/from iterator") has introduced sanity check for copying from/to iov iterator. Lacking of copy direction from the iterator viewpoint would lead to kernel stack trace like above.

This commit fixes this issue by initializing the iov iterator with the correct copy direction when sending SYN or ACK without data.

— MITRE

Linux Kernel is vulnerable to a denial of service, caused by a kernel warning when sending SYN message. By sending a specially crafted request, a local authenticated attacker could exploit this vulnerability to cause a denial of service.

— IBM