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(Upstream commit 50896c410354432e8e7baf97fcdd7df265e683ae.) The syzkaller USB fuzzer identified a failure mode in which dummy-hcd would never give back an unlinked URB. This causes usb_kill_urb() to hang, leading to WARNINGs and unkillable threads. In dummy-hcd, all URBs are given back by the dummy_timer() routine as it scans through the list of pending URBS. Failure to give back URBs can be caused by failure to start or early exit from the scanning loop. The code currently has two such pathways: One is triggered when an unsupported bus transfer speed is encountered, and the other by exhausting the simulated bandwidth for USB transfers during a frame. This patch removes those two paths, thereby allowing all unlinked URBs to be given back in a timely manner. It adds a check for the bus speed when the gadget first starts running, so that dummy_timer() will never thereafter encounter an unsupported speed. And it prevents the loop from exiting as soon as the total bandwidth has been used up (the scanning loop continues, giving back unlinked URBs as they are found, but not transferring any more data). Thanks to Andrey Konovalov for manually running the syzkaller fuzzer to help track down the source of the bug. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-and-tested-by: syzbot+d919b0f29d7b5a4994b9@syzkaller.appspotmail.com CC: <stable@vger.kernel.org> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com> Signed-off-by: Andrey Konovalov <andreyknvl@google.com> Bug: 147413187 Change-Id: I67f054e708130e1c7f252395bc560d6ec0760b24
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.