CVE-2024-47684: tcp: check skb is non-NULL in tcp_rto_delta_us()

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

tcp: check skb is non-NULL in tcprtodeltaus()

We have some machines running stock Ubuntu 20.04.6 which is their 5.4.0-174-generic kernel that are running ceph and recently hit a null ptr dereference in tcprearmrto(). Initially hitting it from the TLP path, but then later we also saw it getting hit from the RACK case as well. Here are examples of the oops messages we saw in each of those cases:

Jul 26 15:05:02 rx [11061395.780353] BUG: kernel NULL pointer dereference, address: 0000000000000020 Jul 26 15:05:02 rx [11061395.787572] #PF: supervisor read access in kernel mode Jul 26 15:05:02 rx [11061395.792971] #PF: errorcode(0x0000) - not-present page Jul 26 15:05:02 rx [11061395.798362] PGD 0 P4D 0 Jul 26 15:05:02 rx [11061395.801164] Oops: 0000 [#1] SMP NOPTI Jul 26 15:05:02 rx [11061395.805091] CPU: 0 PID: 9180 Comm: msgr-worker-1 Tainted: G W 5.4.0-174-generic #193-Ubuntu Jul 26 15:05:02 rx [11061395.814996] Hardware name: Supermicro SMC 2x26 os-gen8 64C NVME-Y 256G/H12SSW-NTR, BIOS 2.5.V1.2U.NVMe.UEFI 05/09/2023 Jul 26 15:05:02 rx [11061395.825952] RIP: 0010:tcprearmrto+0xe4/0x160 Jul 26 15:05:02 rx [11061395.830656] Code: 87 ca 04 00 00 00 5b 41 5c 41 5d 5d c3 c3 49 8b bc 24 40 06 00 00 eb 8d 48 bb cf f7 53 e3 a5 9b c4 20 4c 89 ef e8 0c fe 0e 00 <48> 8b 78 20 48 c1 ef 03 48 89 f8 41 8b bc 24 80 04 00 00 48 f7 e3 Jul 26 15:05:02 rx [11061395.849665] RSP: 0018:ffffb75d40003e08 EFLAGS: 00010246 Jul 26 15:05:02 rx [11061395.855149] RAX: 0000000000000000 RBX: 20c49ba5e353f7cf RCX: 0000000000000000 Jul 26 15:05:02 rx [11061395.862542] RDX: 0000000062177c30 RSI: 000000000000231c RDI: ffff9874ad283a60 Jul 26 15:05:02 rx [11061395.869933] RBP: ffffb75d40003e20 R08: 0000000000000000 R09: ffff987605e20aa8 Jul 26 15:05:02 rx [11061395.877318] R10: ffffb75d40003f00 R11: ffffb75d4460f740 R12: ffff9874ad283900 Jul 26 15:05:02 rx [11061395.884710] R13: ffff9874ad283a60 R14: ffff9874ad283980 R15: ffff9874ad283d30 Jul 26 15:05:02 rx [11061395.892095] FS: 00007f1ef4a2e700(0000) GS:ffff987605e00000(0000) knlGS:0000000000000000 Jul 26 15:05:02 rx [11061395.900438] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 Jul 26 15:05:02 rx [11061395.906435] CR2: 0000000000000020 CR3: 0000003e450ba003 CR4: 0000000000760ef0 Jul 26 15:05:02 rx [11061395.913822] PKRU: 55555554 Jul 26 15:05:02 rx [11061395.916786] Call Trace: Jul 26 15:05:02 rx [11061395.919488] Jul 26 15:05:02 rx [11061395.921765] ? showregs.cold+0x1a/0x1f Jul 26 15:05:02 rx [11061395.925859] ? die+0x90/0xd9 Jul 26 15:05:02 rx [11061395.929169] ? nocontext+0x196/0x380 Jul 26 15:05:02 rx [11061395.933088] ? ip6protocoldeliverrcu+0x4e0/0x4e0 Jul 26 15:05:02 rx [11061395.938216] ? ip6sublistrcvfinish+0x3d/0x50 Jul 26 15:05:02 rx [11061395.943000] ? badareanosemaphore+0x50/0x1a0 Jul 26 15:05:02 rx [11061395.947873] ? badareanosemaphore+0x16/0x20 Jul 26 15:05:02 rx [11061395.952486] ? douseraddrfault+0x267/0x450 Jul 26 15:05:02 rx [11061395.957104] ? ipv6listrcv+0x112/0x140 Jul 26 15:05:02 rx [11061395.961279] ? dopagefault+0x58/0x90 Jul 26 15:05:02 rx [11061395.965458] ? dopagefault+0x2c/0xe0 Jul 26 15:05:02 rx [11061395.969465] ? pagefault+0x34/0x40 Jul 26 15:05:02 rx [11061395.973217] ? tcprearmrto+0xe4/0x160 Jul 26 15:05:02 rx [11061395.977313] ? tcprearmrto+0xe4/0x160 Jul 26 15:05:02 rx [11061395.981408] tcpsendlossprobe+0x10b/0x220 Jul 26 15:05:02 rx [11061395.985937] tcpwritetimerhandler+0x1b4/0x240 Jul 26 15:05:02 rx [11061395.990809] tcpwritetimer+0x9e/0xe0 Jul 26 15:05:02 rx [11061395.994814] ? tcpwritetimerhandler+0x240/0x240 Jul 26 15:05:02 rx [11061395.999866] calltimerfn+0x32/0x130 Jul 26 15:05:02 rx [11061396.003782] runtimers.part.0+0x180/0x280 Jul 26 15:05:02 rx [11061396.008309] ? recalibratecpukhz+0x10/0x10 Jul 26 15:05:02 rx [11061396.012841] ? nativex2apicicrwrite+0x30/0x30 Jul 26 15:05:02 rx [11061396.017718] ? lapicnexteven ---truncated---