In the Linux kernel, the following vulnerability has been resolved: RDMA/rtrs-srv: Bound RDMA-Write length to chunk size in rdma_write_sg

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

RDMA/rtrs-srv: Bound RDMA-Write length to chunk size in rdma_write_sg

When the server answers an RTRS READ, rdma_write_sg() builds the source
scatter/gather entry for the IB_WR_RDMA_WRITE that returns data to the
peer. Its length is taken directly from the wire descriptor:

plist->length = le32_to_cpu(id->rd_msg->desc[0].len);

rd_msg points into the chunk buffer that the remote peer filled via
RDMA-WRITE-WITH-IMM (rtrs_srv_rdma_done() -> process_io_req() ->
process_read()), so desc[0].len is attacker-controlled and, before this
change, was only rejected when zero. The source address is the fixed
chunk start (dma_addr[msg_id]) and the source lkey is the PD-wide
local_dma_lkey, which is not tied to the chunk's MR mapping, so the verbs
layer does not constrain the transfer length to max_chunk_size. msg_id
and off are bounded against queue_depth and max_chunk_size in
rtrs_srv_rdma_done(), but desc[0].len is a separate field that was not
checked against the chunk size.

A peer that advertises desc[0].len larger than max_chunk_size can make
the posted RDMA write read past the chunk's mapped region. The resulting
behaviour depends on the IOMMU configuration: with no IOMMU or in
passthrough mode the read may extend into memory adjacent to the chunk
and be returned to the peer, which can disclose host memory; with a
translating IOMMU the out-of-range access is expected to fault and abort
the connection. In either case the transfer exceeds what the protocol
permits and is driven by a remote peer.

Reject a descriptor length above max_chunk_size, mirroring the existing
off >= max_chunk_size bound in rtrs_srv_rdma_done(). Legitimate clients
do not exceed it: the client sets desc[0].len to its MR length, which is
capped at the negotiated max_io_size (max_chunk_size - MAX_HDR_SIZE).