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

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Date:   Fri, 10 Nov 2017 12:40:39 +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>,
        John Keeping <john@...anate.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:
> 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.

-- 
balbi

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