CVE-2026-80789

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CVE-2026-80789

Summary: nvmet-tcp: bound SGL data length before allocating command buffers

Details: In the Linux kernel, the following vulnerability has been resolved: nvmet-tcp: bound SGL data length before allocating command buffers nvmet_tcp_map_data() reads the host-controlled 32-bit sgl->length and, for the in-capsule offset descriptor (type 0x01), checks it against port->inline_data_size before use. Any other SGL descriptor type -- including the non-inline transport SGL data-block descriptor (type (NVME_TRANSPORT_SGL_DATA_DESC << 4) | NVME_SGL_FMT_TRANSPORT_A, the type a real host uses for out-of-capsule writes) skips that check entirely and falls straight through to: cmd->req.sg = sgl_alloc(len, GFP_KERNEL, &cmd->req.sg_cnt); with len taken directly from the wire, unbounded up to 4 GiB. nvmet_req_init() only parses the command and never inspects sgl->length, and nvmet_check_transfer_len() -- the only other place transfer_len is validated -- runs later, from req->execute(), after the allocation has already happened. For a write command the target responds with an R2T and parks the command waiting for the host to send the data; if the host (or an unauthenticated peer that simply never follows up) never does, the sgl_alloc() buffer stays resident for the life of the command. NVMe/TCP has no mandatory authentication in the default configuration, so any peer able to reach the target portal and complete a Fabrics connect can drive this with a single crafted command, repeatable across queues and connections for amplification. This is unbounded kernel memory allocation triggered by a remote, effectively unauthenticated peer. Validate len against the same NVMET_TCP_MAXH2CDATA ceiling this file already uses to bound per-PDU H2C data, for every SGL descriptor type, before doing any allocation. This closes the gap for the non-inline descriptor while leaving the existing, tighter inline_data_size check in place for the in-capsule case. Runtime-verified on a v6.19 KASAN stand: with this bound in place, a crafted write command carrying an oversized non-inline SGL length is rejected before sgl_alloc() runs, where the same request previously drove an unbounded ~256 MiB kernel allocation (up to 4 GiB) that stayed resident pending an R2T the host never satisfies.

References: https://git.kernel.org/stable/c/0952541b153e258b99d39cdb03ea6919fdeb41d0, https://git.kernel.org/stable/c/14dbe37681a6a7e346fc147bb363ec7cca3180a0, https://git.kernel.org/stable/c/25ad03d5c0e858c4b63f1e4b6d461d2af1b30b22, https://git.kernel.org/stable/c/4a3f00262a044e8e15064b1a6860968bf0500bf4, https://git.kernel.org/stable/c/6d27199ebe8cb223022150f74be13f154a964474, https://git.kernel.org/stable/c/d2acc96c528d589f5827cfb90e8e9229dd9d8cb4, https://git.kernel.org/stable/c/d895e66628f939edbb98608f6e033d3d39e6e546, https://git.kernel.org/stable/c/f63e89a0310264264923f84406dea05fe752de62, https://git.kernel.org/stable/c/f6e51b09cbaa5f6f6e6a3a9dafa666f76c37aab5, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80789.json, https://nvd.nist.gov/vuln/detail/CVE-2026-80789, https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git