On Mon, 2020-05-18 at 16:47 +0000, Saeed Mahameed wrote:
> On Sun, 2020-05-17 at 18:20 +0100, Ben Hutchings wrote:
> > mlx4_en_get_module_eeprom() returns 0 even if it fails. This results
> > in copying an uninitialised (or partly initialised) buffer back to
> > user-space.
[...]
> I am not sure i see the issue in here, and why we need the partial
> memset ?
> first thing in this function we do:
> memset(data, 0, ee->len);
>
> and then mlx4_get_module_info() will only copy valid data only on
> success.
Wow, sorry, I don't know how I missed that. So this is not the bug I
was looking for.
>
> > - if (!ret) /* Done reading */
> > + if (!ret) {
> > + /* DOM was not readable after all */
>
> actually if mlx4_get_module_info() returns any non-negative value it
> means how much data was read, so if it returns 0, it means that this
> was the last iteration and we are done reading the eeprom..
>
> so i would remove the above comment and the memset below is redundant
> since we already memset the whole buffer before the while loop.
Right.
> > + memset(data + i, 0, ee->len - i);
> > return 0;
> > + }
> >
> > if (ret < 0) {
> > en_err(priv,
> > "mlx4_get_module_info i(%d) offset(%d)
> > bytes_to_read(%d) - FAILED (0x%x)\n",
> > i, offset, ee->len - i, ret);
> > - return 0;
> > + return ret;
>
> I think returning error in here was the actual solution for your
> problem. you can verify by looking in the kernel log and verify you see
> the log message.
The original bug report (https://bugs.debian.org/960702) says that
ethtool reports different values depending on whether its output is
redirected. Although returning all-zeroes for the unreadable part
might be wrong, it doesn't explain that behaviour.
Perhaps if the timing of the I²C reads is marginal, varying numbers of
bytes of DOM information might be readable? But I don't see how
redirection of ethtool's output would affect that. It uses a single
ioctl to read everything, and the kernel controls timing within that.
So I am mystified about what is going on here. Maybe there is a bug in
ethtool, but I'm not seeing it.
Ben.
> > }
> >
> > i += ret;
--
Ben Hutchings
The two most common things in the universe are hydrogen and stupidity.
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