[PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT

[PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT

[John Keeping]

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@vger.kernel.org # v4.7+
Signed-off-by: John Keeping <john@metanate.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])
-- 
2.15.0

Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT

[Felipe Balbi]

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Hi,

John Keeping <john@metanate.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@vger.kernel.org # v4.7+
> Signed-off-by: John Keeping <john@metanate.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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Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT

[John Keeping]

On Fri, 10 Nov 2017 12:40:39 +0200, Felipe Balbi wrote:

> John Keeping <john@metanate.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@vger.kernel.org # v4.7+
> > Signed-off-by: John Keeping <john@metanate.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.

At this point I don't think the kernel can disallow any values of
Reserved1 without breaking someone's userspace.

Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT

[Felipe Balbi]

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Hi,

John Keeping <john@metanate.com> writes:
> On Fri, 10 Nov 2017 12:40:39 +0200, Felipe Balbi wrote:
>
>> John Keeping <john@metanate.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@vger.kernel.org # v4.7+
>> > Signed-off-by: John Keeping <john@metanate.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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Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT

[John Keeping]

On Mon, 13 Nov 2017 12:57:21 +0200, Felipe Balbi wrote:
> Good point. Then how about we just force the value to 1 in f_fs.c and
> remove the check?

That seems reasonable.  Something like this?

-- >8 --
Subject: [PATCH] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT

The specification says that the Reserved1 field in OS_DESC_EXT_COMPAT
must have the value "1", but when this feature was first implemented we
rejected any non-zero values.

This was adjusted to accept all non-zero values (while now rejecting
zero) in commit 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on
reserved1 of OS_DESC_EXT_COMPAT"), but that breaks any userspace
programs that worked previously by returning EINVAL when Reserved1 == 0
which was previously the only value that succeeded!

If we just set the field to "1" ourselves, both old and new userspace
programs continue to work correctly and, as a bonus, old programs are
now compliant with the specification without having to fix anything
themselves.

Fixes: 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 of OS_DESC_EXT_COMPAT")
Cc: stable@vger.kernel.org
Signed-off-by: John Keeping <john@metanate.com>
---
 drivers/usb/gadget/function/f_fs.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 652397eda6d6..520a96e7ef9a 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2282,9 +2282,18 @@ 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;
+		if (d->Reserved1 != 1) {
+			/*
+			 * According to the spec, Reserved1 must be set to 1
+			 * but older kernels incorrectly rejected non-zero
+			 * values.  We fix it here to avoid returning EINVAL
+			 * in response to values we used to accept.
+			 */
+			pr_debug("usb_ext_compat_desc::Reserved1 forced to 1\n");
+			d->Reserved1 = 1;
+		}
 		for (i = 0; i < ARRAY_SIZE(d->Reserved2); ++i)
 			if (d->Reserved2[i])
 				return -EINVAL;
-- 
2.15.0

Re: [PATCH] usb: f_fs: Drop check on Reserved1 field on OS_DESC_EXT_COMPAT

[Felipe Balbi]

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Hi,

John Keeping <john@metanate.com> writes:
> On Mon, 13 Nov 2017 12:57:21 +0200, Felipe Balbi wrote:
>> Good point. Then how about we just force the value to 1 in f_fs.c and
>> remove the check?
>
> That seems reasonable.  Something like this?
>
> -- >8 --
> Subject: [PATCH] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT
>
> The specification says that the Reserved1 field in OS_DESC_EXT_COMPAT
> must have the value "1", but when this feature was first implemented we
> rejected any non-zero values.
>
> This was adjusted to accept all non-zero values (while now rejecting
> zero) in commit 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on
> reserved1 of OS_DESC_EXT_COMPAT"), but that breaks any userspace
> programs that worked previously by returning EINVAL when Reserved1 == 0
> which was previously the only value that succeeded!
>
> If we just set the field to "1" ourselves, both old and new userspace
> programs continue to work correctly and, as a bonus, old programs are
> now compliant with the specification without having to fix anything
> themselves.
>
> Fixes: 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 of OS_DESC_EXT_COMPAT")
> Cc: stable@vger.kernel.org
> Signed-off-by: John Keeping <john@metanate.com>
> ---
>  drivers/usb/gadget/function/f_fs.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 652397eda6d6..520a96e7ef9a 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -2282,9 +2282,18 @@ 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;
> +		if (d->Reserved1 != 1) {
> +			/*
> +			 * According to the spec, Reserved1 must be set to 1
> +			 * but older kernels incorrectly rejected non-zero
> +			 * values.  We fix it here to avoid returning EINVAL
> +			 * in response to values we used to accept.
> +			 */
> +			pr_debug("usb_ext_compat_desc::Reserved1 forced to 1\n");
> +			d->Reserved1 = 1;
> +		}

exactly like that. Care to send as a formal patch so I can apply?

-- 
balbi

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[PATCH v2] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT

[John Keeping]

The specification says that the Reserved1 field in OS_DESC_EXT_COMPAT
must have the value "1", but when this feature was first implemented we
rejected any non-zero values.

This was adjusted to accept all non-zero values (while now rejecting
zero) in commit 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on
reserved1 of OS_DESC_EXT_COMPAT"), but that breaks any userspace
programs that worked previously by returning EINVAL when Reserved1 == 0
which was previously the only value that succeeded!

If we just set the field to "1" ourselves, both old and new userspace
programs continue to work correctly and, as a bonus, old programs are
now compliant with the specification without having to fix anything
themselves.

Fixes: 53642399aa71 ("usb: gadget: f_fs: Fix wrong check on reserved1 of OS_DESC_EXT_COMPAT")
Cc: stable@vger.kernel.org
Signed-off-by: John Keeping <john@metanate.com>
---
 drivers/usb/gadget/function/f_fs.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

On Mon, 27 Nov 2017 13:34:20 +0200, Felipe Balbi wrote:

> exactly like that. Care to send as a formal patch so I can apply?

Here it is.

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 97ea059a7aa4..7537cc1a7d79 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2282,9 +2282,18 @@ 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;
+		if (d->Reserved1 != 1) {
+			/*
+			 * According to the spec, Reserved1 must be set to 1
+			 * but older kernels incorrectly rejected non-zero
+			 * values.  We fix it here to avoid returning EINVAL
+			 * in response to values we used to accept.
+			 */
+			pr_debug("usb_ext_compat_desc::Reserved1 forced to 1\n");
+			d->Reserved1 = 1;
+		}
 		for (i = 0; i < ARRAY_SIZE(d->Reserved2); ++i)
 			if (d->Reserved2[i])
 				return -EINVAL;
-- 
2.15.0