In the Linux kernel, the following vulnerability has been resolved: net: fix udp gso skbsegment after pull from fraglist Commit a1e40ac5b5e9 ("net: gso: fix udp gso fraglist segmentation after pull from fraglist") detected invalid geometry in fraglist skbs and redirects them from skbsegmentlist to more robust skbsegment. But some packets with modified geometry can also hit bugs in that code. We don't know how many such cases exist. Addressing each one by one also requires touching the complex skbsegment code, which risks introducing bugs for other types of skbs. Instead, linearize all these packets that fail the basic invariants on gso fraglist skbs. That is more robust. If only part of the fraglist payload is pulled into headskb, it will always cause exception when splitting skbs by skbsegment. For detailed call stack information, see below. Valid SKBGSOFRAGLIST skbs - consist of two or more segments - the headskb holds the protocol headers plus first gsosize - one or more fraglist skbs hold exactly one segment - all but the last must be gsosize Optional datapath hooks such as NAT and BPF (bpfskbpulldata) can modify fraglist skbs, breaking these invariants. In extreme cases they pull one part of data into skb linear. For UDP, this causes three payloads with lengths of (11,11,10) bytes were pulled tail to become (12,10,10) bytes. The skbs no longer meets the above SKBGSOFRAGLIST conditions because payload was pulled into headskb, it needs to be linearized before pass to regular skbsegment. skbsegment+0xcd0/0xd14 _udpgsosegment+0x334/0x5f4 udp4ufofragment+0x118/0x15c inetgsosegment+0x164/0x338 skbmacgsosegment+0xc4/0x13c _skbgsosegment+0xc4/0x124 validatexmitskb+0x9c/0x2c0 validatexmitskblist+0x4c/0x80 schdirectxmit+0x70/0x404 _devqueuexmit+0x64c/0xe5c neighresolveoutput+0x178/0x1c4 ipfinishoutput2+0x37c/0x47c _ipfinishoutput+0x194/0x240 ipfinishoutput+0x20/0xf4 ipoutput+0x100/0x1a0 NFHOOK+0xc4/0x16c ipforward+0x314/0x32c iprcv+0x90/0x118 _netifreceiveskb+0x74/0x124 processbacklog+0xe8/0x1a4 _napipoll+0x5c/0x1f8 netrxaction+0x154/0x314 handlesoftirqs+0x154/0x4b8 [118.376811] [C201134] rxq0pus: [name:bug&]kernel BUG at net/core/skbuff.c:4278! [118.376829] [C201134] rxq0pus: [name:traps&]Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP [118.470774] [C201134] rxq0pus: [name:mrdump&]Kernel Offset: 0x178cc00000 from 0xffffffc008000000 [118.470810] [C201134] rxq0pus: [name:mrdump&]PHYSOFFSET: 0x40000000 [118.470827] [C201134] rxq0pus: [name:mrdump&]pstate: 60400005 (nZCv daif +PAN -UAO) [118.470848] [C201134] rxq0pus: [name:mrdump&]pc : [0xffffffd79598aefc] skbsegment+0xcd0/0xd14 [118.470900] [C201134] rxq0pus: [name:mrdump&]lr : [0xffffffd79598a5e8] skbsegment+0x3bc/0xd14 [118.470928] [C201134] rxq0pus: [name:mrdump&]sp : ffffffc008013770