Re: [PATCH] USB: core: Fix incorrect pipe calculation in do_proc_control()

On Mon, Jul 12, 2021 at 02:54:36PM -0400, Alan Stern wrote:

When the user submits a control URB via usbfs, the user supplies the
bRequestType value and the kernel uses it to compute the pipe value.
However, do_proc_control() performs this computation incorrectly in
the case where the bRequestType direction bit is set to USB_DIR_IN and
the URB's transfer length is 0: The pipe's direction is also set to IN
but it should be OUT, which is the direction the actual transfer will
use regardless of bRequestType.

Commit 5cc59c418fde ("USB: core: WARN if pipe direction != setup
packet direction") added a check to compare the direction bit in the
pipe value to a control URB's actual direction and to WARN if they are
different.  This can be triggered by the incorrect computation
mentioned above, as found by syzbot.

This patch fixes the computation, thus avoiding the WARNing.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: syzbot+72af3105289dcb4c055b@syzkaller.appspotmail.com

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Greg, I'm not sure which -stable kernels, if any, need this.  It should 
go into any kernel which contains 5cc59c418fde.

That's just 5.14-rc1, I asked for AUTOSEL to not take it so we should be
fine.

Thanks for the fix, I'll queue it up now.

greg k-h