linux-kernel - Re: [uwb-i1480] question about value overwrite

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Date:   Fri, 19 May 2017 07:33:31 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [uwb-i1480] question about value overwrite

On Thu, May 18, 2017 at 06:00:06PM -0500, Gustavo A. R. Silva wrote:
> 
> Hello everybody,
> 
> While looking into Coverity ID 1226913 I ran into the following piece of
> code at drivers/uwb/i1480/dfu/phy.c:99:
> 
>  99static
> 100int i1480_mpi_read(struct i1480 *i1480, u8 *data, u16 srcaddr, size_t size)
> 101{
> 102        int result;
> 103        struct i1480_cmd_mpi_read *cmd = i1480->cmd_buf;
> 104        struct i1480_evt_mpi_read *reply = i1480->evt_buf;
> 105        unsigned cnt;
> 106
> 107        memset(i1480->cmd_buf, 0x69, 512);
> 108        memset(i1480->evt_buf, 0x69, 512);
> 109
> 110        BUG_ON(size > (i1480->buf_size - sizeof(*reply)) / 3);
> 111        result = -ENOMEM;
> 112        cmd->rccb.bCommandType = i1480_CET_VS1;
> 113        cmd->rccb.wCommand = cpu_to_le16(i1480_CMD_MPI_READ);
> 114        cmd->size = cpu_to_le16(3*size);
> 115        for (cnt = 0; cnt < size; cnt++) {
> 116                cmd->data[cnt].page = (srcaddr + cnt) >> 8;
> 117                cmd->data[cnt].offset = (srcaddr + cnt) & 0xff;
> 118        }
> 119        reply->rceb.bEventType = i1480_CET_VS1;
> 120        reply->rceb.wEvent = i1480_CMD_MPI_READ;
> 121        result = i1480_cmd(i1480, "MPI-READ", sizeof(*cmd) + 2*size,
> 122                        sizeof(*reply) + 3*size);
> 123        if (result < 0)
> 124                goto out;
> 125        if (reply->bResultCode != UWB_RC_RES_SUCCESS) {
> 126                dev_err(i1480->dev, "MPI-READ: command execution failed:
> %d\n",
> 127                        reply->bResultCode);
> 128                result = -EIO;
> 129        }
> 130        for (cnt = 0; cnt < size; cnt++) {
> 131                if (reply->data[cnt].page != (srcaddr + cnt) >> 8)
> 132                        dev_err(i1480->dev, "MPI-READ: page inconsistency
> at "
> 133                                "index %u: expected 0x%02x, got
> 0x%02x\n", cnt,
> 134                                (srcaddr + cnt) >> 8,
> reply->data[cnt].page);
> 135                if (reply->data[cnt].offset != ((srcaddr + cnt) & 0x00ff))
> 136                        dev_err(i1480->dev, "MPI-READ: offset
> inconsistency at "
> 137                                "index %u: expected 0x%02x, got
> 0x%02x\n", cnt,
> 138                                (srcaddr + cnt) & 0x00ff,
> 139                                reply->data[cnt].offset);
> 140                data[cnt] = reply->data[cnt].value;
> 141        }
> 142        result = 0;
> 143out:
> 144        return result;
> 145}
> 
> The issue is that the value store in variable _result_ at line 128 is
> overwritten by the one stored at line 142, before it can be used.
> 
> My question is if the original intention was to return this value
> inmediately after the assignment at line 128, something like in the
> following patch:
> 
> index 3b1a87d..1ac8526 100644
> --- a/drivers/uwb/i1480/dfu/phy.c
> +++ b/drivers/uwb/i1480/dfu/phy.c
> @@ -126,6 +126,7 @@ int i1480_mpi_read(struct i1480 *i1480, u8 *data, u16
> srcaddr, size_t size)
>                 dev_err(i1480->dev, "MPI-READ: command execution failed:
> %d\n",
>                         reply->bResultCode);
>                 result = -EIO;
> +               goto out;
>         }
>         for (cnt = 0; cnt < size; cnt++) {
>                 if (reply->data[cnt].page != (srcaddr + cnt) >> 8)
> 
> What do you think?
> 
> I'd really appreciate any comment on this.

I think you are correct, I'll take a patch to fix this up if you want to
write one :)

thanks,

greg k-h