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    Subject[PATCH AUTOSEL 4.14 16/33] USB: core: Avoid WARNings for 0-length descriptor requests
    Date
    From: Alan Stern <stern@rowland.harvard.edu>

    [ Upstream commit 60dfe484cef45293e631b3a6e8995f1689818172 ]

    The USB core has utility routines to retrieve various types of
    descriptors. These routines will now provoke a WARN if they are asked
    to retrieve 0 bytes (USB "receive" requests must not have zero
    length), so avert this by checking the size argument at the start.

    CC: Johan Hovold <johan@kernel.org>
    Reported-and-tested-by: syzbot+7dbcd9ff34dc4ed45240@syzkaller.appspotmail.com
    Reviewed-by: Johan Hovold <johan@kernel.org>
    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    Link: https://lore.kernel.org/r/20210607152307.GD1768031@rowland.harvard.edu
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/usb/core/message.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
    index 7337d8f317aa..ff785b52da99 100644
    --- a/drivers/usb/core/message.c
    +++ b/drivers/usb/core/message.c
    @@ -645,6 +645,9 @@ int usb_get_descriptor(struct usb_device *dev, unsigned char type,
    int i;
    int result;

    + if (size <= 0) /* No point in asking for no data */
    + return -EINVAL;
    +
    memset(buf, 0, size); /* Make sure we parse really received data */

    for (i = 0; i < 3; ++i) {
    @@ -693,6 +696,9 @@ static int usb_get_string(struct usb_device *dev, unsigned short langid,
    int i;
    int result;

    + if (size <= 0) /* No point in asking for no data */
    + return -EINVAL;
    +
    for (i = 0; i < 3; ++i) {
    /* retry on length 0 or stall; some devices are flakey */
    result = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
    --
    2.30.2
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