CVE-2024-26863: hsr: Fix uninit-value access in hsr_get_node()

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

hsr: Fix uninit-value access in hsrgetnode()

KMSAN reported the following uninit-value access issue [1]:

===================================================== BUG: KMSAN: uninit-value in hsrgetnode+0xa2e/0xa40 net/hsr/hsrframereg.c:246 hsrgetnode+0xa2e/0xa40 net/hsr/hsrframereg.c:246 fillframeinfo net/hsr/hsrforward.c:577 [inline] hsrforwardskb+0xe12/0x30e0 net/hsr/hsrforward.c:615 hsrdevxmit+0x1a1/0x270 net/hsr/hsrdevice.c:223 netdevstartxmit include/linux/netdevice.h:4940 [inline] netdevstartxmit include/linux/netdevice.h:4954 [inline] xmitone net/core/dev.c:3548 [inline] devhardstartxmit+0x247/0xa10 net/core/dev.c:3564 devqueuexmit+0x33b8/0x5130 net/core/dev.c:4349 devqueuexmit include/linux/netdevice.h:3134 [inline] packetxmit+0x9c/0x6b0 net/packet/afpacket.c:276 packetsnd net/packet/afpacket.c:3087 [inline] packetsendmsg+0x8b1d/0x9f30 net/packet/afpacket.c:3119 socksendmsgnosec net/socket.c:730 [inline] socksendmsg net/socket.c:745 [inline] syssendto+0x735/0xa10 net/socket.c:2191 dosyssendto net/socket.c:2203 [inline] sesyssendto net/socket.c:2199 [inline] x64syssendto+0x125/0x1c0 net/socket.c:2199 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0x6d/0x140 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x63/0x6b

Uninit was created at: slabpostallochook+0x129/0xa70 mm/slab.h:768 slaballocnode mm/slub.c:3478 [inline] kmemcacheallocnode+0x5e9/0xb10 mm/slub.c:3523 kmallocreserve+0x13d/0x4a0 net/core/skbuff.c:560 allocskb+0x318/0x740 net/core/skbuff.c:651 allocskb include/linux/skbuff.h:1286 [inline] allocskbwithfrags+0xc8/0xbd0 net/core/skbuff.c:6334 sockallocsendpskb+0xa80/0xbf0 net/core/sock.c:2787 packetallocskb net/packet/afpacket.c:2936 [inline] packetsnd net/packet/afpacket.c:3030 [inline] packetsendmsg+0x70e8/0x9f30 net/packet/afpacket.c:3119 socksendmsgnosec net/socket.c:730 [inline] socksendmsg net/socket.c:745 [inline] syssendto+0x735/0xa10 net/socket.c:2191 dosyssendto net/socket.c:2203 [inline] sesyssendto net/socket.c:2199 [inline] x64syssendto+0x125/0x1c0 net/socket.c:2199 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0x6d/0x140 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x63/0x6b

CPU: 1 PID: 5033 Comm: syz-executor334 Not tainted 6.7.0-syzkaller-00562-g9f8413c4a66f #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023 =====================================================

If the packet type ID field in the Ethernet header is either ETHPPRP or ETHPHSR, but it is not followed by an HSR tag, hsrgetskbsequencenr() reads an invalid value as a sequence number. This causes the above issue.

This patch fixes the issue by returning NULL if the Ethernet header is not followed by an HSR tag.