CVE-2024-36927: ipv4: Fix uninit-value access in __ip_make_skb()

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

ipv4: Fix uninit-value access in ipmakeskb()

KMSAN reported uninit-value access in ipmakeskb() [1]. ipmakeskb() tests HDRINCL to know if the skb has icmphdr. However, HDRINCL can cause a race condition. If calling setsockopt(2) with IPHDRINCL changes HDRINCL while ipmakeskb() is running, the function will access icmphdr in the skb even if it is not included. This causes the issue reported by KMSAN.

Check FLOWIFLAGKNOWNNH on fl4->flowi4flags instead of testing HDRINCL on the socket.

Also, fl4->fl4icmptype and fl4->fl4icmpcode are not initialized. These are union in struct flowi4 and are implicitly initialized by flowi4initoutput(), but we should not rely on specific union layout.

Initialize these explicitly in rawsendmsg().

[1] BUG: KMSAN: uninit-value in ipmakeskb+0x2b74/0x2d20 net/ipv4/ipoutput.c:1481 ipmakeskb+0x2b74/0x2d20 net/ipv4/ipoutput.c:1481 ipfinishskb include/net/ip.h:243 [inline] ippushpendingframes+0x4c/0x5c0 net/ipv4/ipoutput.c:1508 rawsendmsg+0x2381/0x2690 net/ipv4/raw.c:654 inetsendmsg+0x27b/0x2a0 net/ipv4/afinet.c:851 socksendmsgnosec net/socket.c:730 [inline] socksendmsg+0x274/0x3c0 net/socket.c:745 syssendto+0x62c/0x7b0 net/socket.c:2191 dosyssendto net/socket.c:2203 [inline] sesyssendto net/socket.c:2199 [inline] x64syssendto+0x130/0x200 net/socket.c:2199 dosyscall64+0xd8/0x1f0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x6d/0x75

Uninit was created at: slabpostallochook mm/slub.c:3804 [inline] slaballocnode mm/slub.c:3845 [inline] kmemcacheallocnode+0x5f6/0xc50 mm/slub.c:3888 kmallocreserve+0x13c/0x4a0 net/core/skbuff.c:577 allocskb+0x35a/0x7c0 net/core/skbuff.c:668 allocskb include/linux/skbuff.h:1318 [inline] ipappenddata+0x49ab/0x68c0 net/ipv4/ipoutput.c:1128 ipappenddata+0x1e7/0x260 net/ipv4/ipoutput.c:1365 rawsendmsg+0x22b1/0x2690 net/ipv4/raw.c:648 inetsendmsg+0x27b/0x2a0 net/ipv4/afinet.c:851 socksendmsgnosec net/socket.c:730 [inline] socksendmsg+0x274/0x3c0 net/socket.c:745 syssendto+0x62c/0x7b0 net/socket.c:2191 dosyssendto net/socket.c:2203 [inline] sesyssendto net/socket.c:2199 [inline] x64syssendto+0x130/0x200 net/socket.c:2199 dosyscall64+0xd8/0x1f0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x6d/0x75

CPU: 1 PID: 15709 Comm: syz-executor.7 Not tainted 6.8.0-11567-gb3603fcb79b1 #25 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014