CVE-2026-46133

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

RDMA/rxe: Reject unknown opcodes before ICRC processing

Even after applying commit 7244491dab34 ("RDMA/rxe: Validate pad and ICRC

before payload_size() in rxe_rcv"), a single unauthenticated UDP packet

can still trigger panic. That patch handled payload_size() underflow only

for valid opcodes with short packets, not for packets carrying an unknown

opcode. The unknown-opcode OOB read described below predates that commit

and reaches back to the initial Soft RoCE driver.

The check added there reads

pkt->paylen < header_size(pkt) + bth_pad(pkt) + RXE_ICRC_SIZE

where header_size(pkt) expands to rxe_opcode[pkt->opcode].length. The

rxe_opcode[] array has 256 entries but is only populated for defined IB

opcodes; any other entry (for example opcode 0xff) is zero-initialized, so

length == 0 and the check degenerates to

pkt->paylen < 0 + bth_pad(pkt) + RXE_ICRC_SIZE

which does not constrain pkt->paylen enough. rxe_icrc_hdr() then computes

rxe_opcode[pkt->opcode].length - RXE_BTH_BYTES

which underflows when length == 0 and passes a huge value to rxe_crc32(),

causing an out-of-bounds read of the skb payload.

Reproduced on v7.0-rc7 with that fix applied, QEMU/KVM with

CONFIG_RDMA_RXE=y and CONFIG_KASAN=y, after

rdma link add rxe0 type rxe netdev eth0

A single 48-byte UDP packet to port 4791 with BTH opcode=0xff and

QPN=IB_MULTICAST_QPN triggers:

BUG: KASAN: slab-out-of-bounds in crc32_le+0x115/0x170

Read of size 1 at addr ...

The buggy address is located 0 bytes to the right of

allocated 704-byte region

Call Trace:

crc32_le+0x115/0x170

rxe_icrc_hdr.isra.0+0x226/0x300

rxe_icrc_check+0x13f/0x3a0

rxe_rcv+0x6e1/0x16e0

rxe_udp_encap_recv+0x20a/0x320

udp_queue_rcv_one_skb+0x7ed/0x12c0

Subsequent packets with the same shape fault on unmapped memory and panic

the kernel. The trigger requires only module load and "rdma link add"; no

QP, no connection, and no authentication.

Fix this by rejecting packets whose opcode has no rxe_opcode[] entry,

detected via the zero mask or zero length, before any length arithmetic

runs.