linux-kernel - Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT

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Date:   Mon, 13 Nov 2017 12:57:21 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     John Keeping <john@...anate.com>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vincent Pelletier <plr.vincent@...il.com>,
        Jim Lin <jilin@...dia.com>,
        Janusz Dziedzic <januszx.dziedzic@...ux.intel.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT


Hi,

John Keeping <john@...anate.com> writes:
> On Fri, 10 Nov 2017 12:40:39 +0200, Felipe Balbi wrote:
>
>> John Keeping <john@...anate.com> writes:
>> > This check has gone through several incompatible variations in commits
>> > 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 of
>> > OS_DESC_EXT_COMPAT"), 354bc45bf329 ("usb: gadget: f_fs: Fix ExtCompat
>> > descriptor validation") and 3ba534df815f ("Revert "usb: gadget: f_fs:
>> > Fix ExtCompat descriptor validation"") after initially being introduced
>> > in commit f0175ab51993 ("usb: gadget: f_fs: OS descriptors support").
>> >
>> > The various changes make it impossible for a single userspace
>> > implementation to work with different kernel versions, so let's just
>> > drop the condition to avoid breaking userspace.
>> >
>> > Fixes: 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 of OS_DESC_EXT_COMPAT")
>> > Cc: stable@...r.kernel.org # v4.7+
>> > Signed-off-by: John Keeping <john@...anate.com>
>> > ---
>> >  drivers/usb/gadget/function/f_fs.c | 3 +--
>> >  1 file changed, 1 insertion(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
>> > index 652397eda6d6..0d9962834345 100644
>> > --- a/drivers/usb/gadget/function/f_fs.c
>> > +++ b/drivers/usb/gadget/function/f_fs.c
>> > @@ -2282,8 +2282,7 @@ static int __ffs_data_do_os_desc(enum ffs_os_desc_type type,
>> >  		int i;
>> >  
>> >  		if (len < sizeof(*d) ||
>> > -		    d->bFirstInterfaceNumber >= ffs->interfaces_count ||
>> > -		    !d->Reserved1)
>> > +		    d->bFirstInterfaceNumber >= ffs->interfaces_count)
>> >  			return -EINVAL;
>> >  		for (i = 0; i < ARRAY_SIZE(d->Reserved2); ++i)
>> >  			if (d->Reserved2[i])  
>> 
>> Sorry, but no. We want to be compliant with the specification. If there
>> are older still-maintained stable trees which are not working, we need
>> to backport a fix to them, but we're not allowing uncompliant
>> implementations.
>
> Aren't we allowing non-compliant implementations now?  The spec says the
> value must be 1 but since v4.7 this code has allowed all non-zero
> values.

Good point. Then how about we just force the value to 1 in f_fs.c and
remove the check?

-- 
balbi

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