Date: Fri, 25 Mar 2005 22:02:45 -0700 From: "Kenneth D. Merry" <ken@kdm.org> To: Henry Miller <hank@blackhole.com> Cc: freebsd-scsi@freebsd.org Subject: Re: scsi_ch issues Message-ID: <20050326050245.GA59378@nargothrond.kdm.org> In-Reply-To: <380-220053222163355859@blackhole.com> References: <380-220053222163355859@blackhole.com>
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On Tue, Mar 22, 2005 at 10:33:55 -0600, Henry Miller wrote:
>
> I posted a summery of this to -questions earlier this morning (you
> can read it there if you want background), I've dug into it more, and
> I think there is a bug in
> cam/scsi/scsi_ch.c
> function chgetelemstatus.
>
> The short summery is my tape changer says that PVOLTAG in pg_hdr is
> FALSE, (or zeroed latter) in the first request of
> scsi_read_element_status() (which freeBSD uses only to get the length
> of the data) on one of my changers, and thus chio(1) will not show
> the bar code label. pg_hdr is not updated to reflect the location
> of result of the second call, when this flag is set. Worse, it looks
> like the results of the first call is a dead pointer by the time it
> checks anyway. Unless free/malloc work different in the kernel from
> userland this is a problem.
>
> I've sniped out a lot of extra code so you can see what I mean.
>
>
> data = (caddr_t)malloc(1024, M_DEVBUF, M_WAITOK);
> --- Fill data to get size
> pg_hdr = \* data + some offset *\
> /*
> * Reallocate storage for descriptors and get them from the
> * device.
> */
> free(data, M_DEVBUF);
> data = (caddr_t)malloc(size, M_DEVBUF, M_WAITOK);
> --- Fill data
> copy_element_status(softc, pg_hdr->flags, desc, ces);
>
> Note that pg_hdr is not valid at this point anyway.
>
> This more or less happens in 4.x, 5.x and current if I read the code
> correctly.
>
> Can someone who knows kernel code better than I look at this.
> Should I send a pr?
>
> Here is a patch against 4.9 (where I first found this problem) that
> might help to understand the fix. I think it needs to be ported to
> all versions. (and perhaps netbsd if there is where we get the
> code?)
>
>
> *** scsi_ch.c.old Tue Mar 22 11:16:15 2005
> --- scsi_ch.c Tue Mar 22 11:09:13 2005
> ***************
> *** 1184,1189 ****
> --- 1184,1192 ----
> * Fill in the user status array.
> */
> st_hdr = (struct read_element_status_header *)data;
> + pg_hdr = (struct read_element_status_page_header
> *)((uintptr_t)st_hdr
> +
> + sizeof(struct read_element_status_header));
> +
> avail = scsi_2btoul(st_hdr->count);
>
> if (avail != cesr->cesr_element_count) {
I just checked this in as rev 1.42 of scsi_ch.c in -current.
I put in a MFC request for RELENG_5, maybe it'll get in in time for 5.4.
Thanks for the fix.
Ken
--
Kenneth Merry
ken@kdm.org
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