CVE-2023-52778

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

mptcp: deal with large GSO size

After the blamed commit below, the TCP sockets (and the MPTCP subflows) can build egress packets larger than 64K. That exceeds the maximum DSS data size, the length being misrepresent on the wire and the stream being corrupted, as later observed on the receiver:

WARNING: CPU: 0 PID: 9696 at net/mptcp/protocol.c:705 _mptcpmoveskbsfromsubflow+0x2604/0x26e0 CPU: 0 PID: 9696 Comm: syz-executor.7 Not tainted 6.6.0-rc5-gcd8bdf563d46 #45 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014 netlink: 8 bytes leftover after parsing attributes in process syz-executor.4'. RIP: 0010:__mptcp_move_skbs_from_subflow+0x2604/0x26e0 net/mptcp/protocol.c:705 RSP: 0018:ffffc90000006e80 EFLAGS: 00010246 RAX: ffffffff83e9f674 RBX: ffff88802f45d870 RCX: ffff888102ad0000 netlink: 8 bytes leftover after parsing attributes in processsyz-executor.4'. RDX: 0000000080000303 RSI: 0000000000013908 RDI: 0000000000003908 RBP: ffffc90000007110 R08: ffffffff83e9e078 R09: 1ffff1100e548c8a R10: dffffc0000000000 R11: ffffed100e548c8b R12: 0000000000013908 R13: dffffc0000000000 R14: 0000000000003908 R15: 000000000031cf29 FS: 00007f239c47e700(0000) GS:ffff88811b200000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f239c45cd78 CR3: 000000006a66c006 CR4: 0000000000770ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600 PKRU: 55555554 Call Trace: <IRQ> mptcpdataready+0x263/0xac0 net/mptcp/protocol.c:819 subflowdataready+0x268/0x6d0 net/mptcp/subflow.c:1409 tcpdataqueue+0x21a1/0x7a60 net/ipv4/tcpinput.c:5151 tcprcvestablished+0x950/0x1d90 net/ipv4/tcpinput.c:6098 tcpv6dorcv+0x554/0x12f0 net/ipv6/tcpipv6.c:1483 tcpv6rcv+0x2e26/0x3810 net/ipv6/tcpipv6.c:1749 ip6protocoldeliverrcu+0xd6b/0x1ae0 net/ipv6/ip6input.c:438 ip6input+0x1c5/0x470 net/ipv6/ip6input.c:483 ipv6rcv+0xef/0x2c0 include/linux/netfilter.h:304 _netifreceiveskb+0x1ea/0x6a0 net/core/dev.c:5532 processbacklog+0x353/0x660 net/core/dev.c:5974 _napipoll+0xc6/0x5a0 net/core/dev.c:6536 netrxaction+0x6a0/0xfd0 net/core/dev.c:6603 _dosoftirq+0x184/0x524 kernel/softirq.c:553 dosoftirq+0xdd/0x130 kernel/softirq.c:454

Address the issue explicitly bounding the maximum GSO size to what MPTCP actually allows.