4.9-stable review patch. If anyone has any objections, please let me know.
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From: John Keeping john@metanate.com
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") Signed-off-by: John Keeping john@metanate.com Signed-off-by: Felipe Balbi felipe.balbi@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/usb/gadget/function/f_fs.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
--- 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 ff 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;