published September 4, 2026
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.