* [PATCH/backport-4.9] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT
@ 2017-12-11 11:02 John Keeping
2017-12-12 8:23 ` Greg KH
0 siblings, 1 reply; 2+ messages in thread
From: John Keeping @ 2017-12-11 11:02 UTC (permalink / raw)
To: stable; +Cc: gregkh, John Keeping, Felipe Balbi
commit a3acc696085e112733d191a77b106e67a4fa110b upstream.
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>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.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 4fce83266926..346a630cebd5 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -2262,9 +2262,18 @@ 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;
--
2.15.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH/backport-4.9] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT
2017-12-11 11:02 [PATCH/backport-4.9] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT John Keeping
@ 2017-12-12 8:23 ` Greg KH
0 siblings, 0 replies; 2+ messages in thread
From: Greg KH @ 2017-12-12 8:23 UTC (permalink / raw)
To: John Keeping; +Cc: stable, Felipe Balbi
On Mon, Dec 11, 2017 at 11:02:51AM +0000, John Keeping wrote:
> commit a3acc696085e112733d191a77b106e67a4fa110b upstream.
Thanks for the backport!
greg k-h
^ permalink raw reply [flat|nested] 2+ messages in thread
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2017-12-11 11:02 [PATCH/backport-4.9] usb: f_fs: Force Reserved1=1 in OS_DESC_EXT_COMPAT John Keeping
2017-12-12 8:23 ` Greg KH
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