netdev - Re: warn in ncsi netlink code

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Message-ID: <74BE39CB-E770-4526-9FCD-CC602178E26F@mendozajonas.com>
Date:   Sun, 20 Nov 2022 11:27:14 +1100
From:   Sam Mendoza-Jonas <sam@...dozajonas.com>
To:     Joel Stanley <joel@....id.au>, Networking <netdev@...r.kernel.org>
CC:     Kees Cook <keescook@...gle.com>
Subject: Re: warn in ncsi netlink code

On November 17, 2022 3:35:17 PM GMT+11:00, Joel Stanley <joel@....id.au> wrote:
>next-20221114 running on an ast2600 system produced this:
>
>[   44.627332] ------------[ cut here ]------------
>[   44.632657] WARNING: CPU: 0 PID: 508 at net/ncsi/ncsi-cmd.c:231
>ncsi_cmd_handler_oem+0xbc/0xd0
>[   44.642387] memcpy: detected field-spanning write (size 7) of
>single field "&cmd->mfr_id" at net/ncsi/ncsi-cmd.c:231 (size 4)
>[   44.655131] CPU: 0 PID: 508 Comm: ncsi-netlink Not tainted
>6.1.0-rc5-14066-gefbdad8553d8 #17
>[   44.664577] Hardware name: Generic DT based system
>[   44.664599]  unwind_backtrace from show_stack+0x18/0x1c
>[   44.675801]  show_stack from dump_stack_lvl+0x40/0x4c
>[   44.681458]  dump_stack_lvl from __warn+0xb8/0x12c
>[   44.686814]  __warn from warn_slowpath_fmt+0x9c/0xd8
>[   44.692370]  warn_slowpath_fmt from ncsi_cmd_handler_oem+0xbc/0xd0
>[   44.699285]  ncsi_cmd_handler_oem from ncsi_xmit_cmd+0x160/0x29c
>[   44.706002]  ncsi_xmit_cmd from ncsi_send_cmd_nl+0x13c/0x1dc
>[   44.712337]  ncsi_send_cmd_nl from genl_rcv_msg+0x1d0/0x440
>[   44.718579]  genl_rcv_msg from netlink_rcv_skb+0xc0/0x120
>[   44.724623]  netlink_rcv_skb from genl_rcv+0x28/0x3c
>[   44.730182]  genl_rcv from netlink_unicast+0x208/0x370
>[   44.735934]  netlink_unicast from netlink_sendmsg+0x1e4/0x450
>[   44.742365]  netlink_sendmsg from ____sys_sendmsg+0x23c/0x2b8
>[   44.748799]  ____sys_sendmsg from ___sys_sendmsg+0x9c/0xd0
>[   44.754941]  ___sys_sendmsg from sys_sendmsg+0x78/0xbc
>[   44.760695]  sys_sendmsg from ret_fast_syscall+0x0/0x54
>[   44.766544] Exception stack(0xb57b1fa8 to 0xb57b1ff0)
>[   44.772191] 1fa0:                   0244f330 0244f1e0 00000003
>7ee36a60 00000000 00000000
>[   44.781328] 1fc0: 0244f330 0244f1e0 76f35c60 00000128 76f91550
>0244f387 0244f387 00498e7c
>[   44.790462] 1fe0: 76f35d34 7ee36a10 76f1b510 76bba140
>[   44.796186] ---[ end trace 0000000000000000 ]---
>
>The relevant code:
>
>static int ncsi_cmd_handler_oem(struct sk_buff *skb,
>                                struct ncsi_cmd_arg *nca)
>{
>        struct ncsi_cmd_oem_pkt *cmd;
>        unsigned int len;
>        int payload;
>        /* NC-SI spec DSP_0222_1.2.0, section 8.2.2.2
>         * requires payload to be padded with 0 to
>         * 32-bit boundary before the checksum field.
>         * Ensure the padding bytes are accounted for in
>         * skb allocation
>         */
>
>        payload = ALIGN(nca->payload, 4);
>        len = sizeof(struct ncsi_cmd_pkt_hdr) + 4;
>        len += max(payload, padding_bytes);
>
>        cmd = skb_put_zero(skb, len);
>        memcpy(&cmd->mfr_id, nca->data, nca->payload);
>        ncsi_cmd_build_header(&cmd->cmd.common, nca);
>
>        return 0;
>}
>
>I think it's copying the command payload to the command packet,
>starting at the offset of mfr_id:
>
>struct ncsi_cmd_oem_pkt {
>        struct ncsi_cmd_pkt_hdr cmd;         /* Command header    */
>        __be32                  mfr_id;      /* Manufacture ID    */
>        unsigned char           data[];      /* OEM Payload Data  */
>};
>
>But I'm not too sure.
>
>Cheers,
>
>Joel


While it looks a little gross I'm pretty sure this is the intended behavior for the OEM commands. We'll need to massage that into something nicer.

Thanks!
Sam