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

[Jason Gunthorpe]

On Tue, Apr 14, 2026 at 07:15:55AM -0400, Michael Bommarito wrote:
> 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@xxxxxxxxxxxxxxx
> Assisted-by: Claude:claude-opus-4-6
> Signed-off-by: Michael Bommarito <michael.bommarito@xxxxxxxxx>
> Reviewed-by: Zhu Yanjun <yanjun.zhu@xxxxxxxxx>
> ---
> 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@xxxxxxxxxx.
> 
>  drivers/infiniband/sw/rxe/rxe_recv.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)

Applied to rc thanks

Jason