CVE-2024-26857: geneve: make sure to pull inner header in geneve_rx()

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

geneve: make sure to pull inner header in geneverx()

syzbot triggered a bug in geneverx() [1]

Issue is similar to the one I fixed in commit 8d975c15c0cd ("ip6tunnel: make sure to pull inner header in ip6tnlrcv()")

We have to save skb->networkheader in a temporary variable in order to be able to recompute the networkheader pointer after a pskbinetmaypull() call.

pskbinetmaypull() makes sure the needed headers are in skb->head.

[1] BUG: KMSAN: uninit-value in IPECNdecapsulate include/net/inetecn.h:302 [inline] BUG: KMSAN: uninit-value in geneverx drivers/net/geneve.c:279 [inline] BUG: KMSAN: uninit-value in geneveudpencaprecv+0x36f9/0x3c10 drivers/net/geneve.c:391 IPECNdecapsulate include/net/inetecn.h:302 [inline] geneverx drivers/net/geneve.c:279 [inline] geneveudpencaprecv+0x36f9/0x3c10 drivers/net/geneve.c:391 udpqueuercvoneskb+0x1d39/0x1f20 net/ipv4/udp.c:2108 udpqueuercvskb+0x6ae/0x6e0 net/ipv4/udp.c:2186 udpunicastrcvskb+0x184/0x4b0 net/ipv4/udp.c:2346 udp4librcv+0x1c6b/0x3010 net/ipv4/udp.c:2422 udprcv+0x7d/0xa0 net/ipv4/udp.c:2604 ipprotocoldeliverrcu+0x264/0x1300 net/ipv4/ipinput.c:205 iplocaldeliverfinish+0x2b8/0x440 net/ipv4/ipinput.c:233 NFHOOK include/linux/netfilter.h:314 [inline] iplocaldeliver+0x21f/0x490 net/ipv4/ipinput.c:254 dstinput include/net/dst.h:461 [inline] iprcvfinish net/ipv4/ipinput.c:449 [inline] NFHOOK include/linux/netfilter.h:314 [inline] iprcv+0x46f/0x760 net/ipv4/ipinput.c:569 netifreceiveskbonecore net/core/dev.c:5534 [inline] netifreceiveskb+0x1a6/0x5a0 net/core/dev.c:5648 processbacklog+0x480/0x8b0 net/core/dev.c:5976 napipoll+0xe3/0x980 net/core/dev.c:6576 napipoll net/core/dev.c:6645 [inline] netrxaction+0x8b8/0x1870 net/core/dev.c:6778 dosoftirq+0x1b7/0x7c5 kernel/softirq.c:553 dosoftirq+0x9a/0xf0 kernel/softirq.c:454 localbhenableip+0x9b/0xa0 kernel/softirq.c:381 localbhenable include/linux/bottomhalf.h:33 [inline] rcureadunlockbh include/linux/rcupdate.h:820 [inline] devqueuexmit+0x2768/0x51c0 net/core/dev.c:4378 devqueuexmit include/linux/netdevice.h:3171 [inline] packetxmit+0x9c/0x6b0 net/packet/afpacket.c:276 packetsnd net/packet/afpacket.c:3081 [inline] packetsendmsg+0x8aef/0x9f10 net/packet/afpacket.c:3113 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+0xcf/0x1e0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x63/0x6b

Uninit was created at: slabpostallochook mm/slub.c:3819 [inline] slaballocnode mm/slub.c:3860 [inline] kmemcacheallocnode+0x5cb/0xbc0 mm/slub.c:3903 kmallocreserve+0x13d/0x4a0 net/core/skbuff.c:560 allocskb+0x352/0x790 net/core/skbuff.c:651 allocskb include/linux/skbuff.h:1296 [inline] allocskbwithfrags+0xc8/0xbd0 net/core/skbuff.c:6394 sockallocsendpskb+0xa80/0xbf0 net/core/sock.c:2783 packetallocskb net/packet/afpacket.c:2930 [inline] packetsnd net/packet/afpacket.c:3024 [inline] packetsendmsg+0x70c2/0x9f10 net/packet/afpacket.c:3113 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+0xcf/0x1e0 arch/x86/entry/common.c:83 entrySYSCALL64afterhwframe+0x63/0x6b