[PATCH v2] RDMA/rxe: Reject unknown opcodes before ICRC processing

[Michael Bommarito <michael.bommarito@gmail.com>]

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.

Fixes: 8700e3e7c485 ("Soft RoCE driver")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
---
v2: also check rxe_opcode[].length per Zhu Yanjun; "||" rather than
    "&&" so the guard tracks the actual underflow in rxe_icrc_hdr().

v1 was sent privately to security@kernel.org.

 drivers/infiniband/sw/rxe/rxe_recv.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/infiniband/sw/rxe/rxe_recv.c b/drivers/infiniband/sw/rxe/rxe_recv.c
index f79214738c2b..2d5e701ff961 100644
--- a/drivers/infiniband/sw/rxe/rxe_recv.c
+++ b/drivers/infiniband/sw/rxe/rxe_recv.c
@@ -330,6 +330,17 @@ void rxe_rcv(struct sk_buff *skb)
 	pkt->qp = NULL;
 	pkt->mask |= rxe_opcode[pkt->opcode].mask;
 
+	/*
+	 * Unknown opcodes have a zero-initialized rxe_opcode[] entry, so
+	 * both mask and length are 0.  Reject them before any length math:
+	 * rxe_icrc_hdr() would otherwise compute length - RXE_BTH_BYTES
+	 * and pass the underflowed value to rxe_crc32(), producing an
+	 * out-of-bounds read.
+	 */
+	if (unlikely(!rxe_opcode[pkt->opcode].mask ||
+		     !rxe_opcode[pkt->opcode].length))
+		goto drop;
+
 	if (unlikely(pkt->paylen < header_size(pkt) + bth_pad(pkt) +
 		       RXE_ICRC_SIZE))
 		goto drop;
-- 
2.53.0