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The dummy-hcd HCD/UDC emulator tries not to do too much work during each timer interrupt. But it doesn't try very hard; currently all it does is limit the total amount of bulk data transferred. Other transfer types aren't limited, and URBs that transfer no data (because of an error, perhaps) don't count toward the limit, even though on a real USB bus they would consume at least a minimum overhead. This means it's possible to get the driver stuck in an infinite loop, for example, if the host class driver resubmits an URB every time it completes (which is common for interrupt URBs). Each time the URB is resubmitted it gets added to the end of the pending-URBs list, and dummy-hcd doesn't stop until that list is empty. Andrey Konovalov was able to trigger this failure mode using the syzkaller fuzzer. This patch fixes the infinite-loop problem by restricting the URBs handled during each timer interrupt to those that were already on the pending list when the interrupt routine started. Newly added URBs won't be processed until the next timer interrupt. The problem of properly accounting for non-bulk bandwidth (as well as packet and transaction overhead) is not addressed here. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-by: Andrey Konovalov <andreyknvl@google.com> Tested-by: Andrey Konovalov <andreyknvl@google.com> CC: <stable@vger.kernel.org> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
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.