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Andrey Konovalov reports that fuzz testing with syzkaller causes a KASAN use-after-free bug report in gadgetfs: BUG: KASAN: use-after-free in gadgetfs_setup+0x208a/0x20e0 at addr ffff88003dfe5bf2 Read of size 2 by task syz-executor0/22994 CPU: 3 PID: 22994 Comm: syz-executor0 Not tainted 4.9.0-rc7+ #16 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 ffff88006df06a18 ffffffff81f96aba ffffffffe0528500 1ffff1000dbe0cd6 ffffed000dbe0cce ffff88006df068f0 0000000041b58ab3 ffffffff8598b4c8 ffffffff81f96828 1ffff1000dbe0ccd ffff88006df06708 ffff88006df06748 Call Trace: <IRQ> [ 201.343209] [< inline >] __dump_stack lib/dump_stack.c:15 <IRQ> [ 201.343209] [<ffffffff81f96aba>] dump_stack+0x292/0x398 lib/dump_stack.c:51 [<ffffffff817e4dec>] kasan_object_err+0x1c/0x70 mm/kasan/report.c:159 [< inline >] print_address_description mm/kasan/report.c:197 [<ffffffff817e5080>] kasan_report_error+0x1f0/0x4e0 mm/kasan/report.c:286 [< inline >] kasan_report mm/kasan/report.c:306 [<ffffffff817e562a>] __asan_report_load_n_noabort+0x3a/0x40 mm/kasan/report.c:337 [< inline >] config_buf drivers/usb/gadget/legacy/inode.c:1298 [<ffffffff8322c8fa>] gadgetfs_setup+0x208a/0x20e0 drivers/usb/gadget/legacy/inode.c:1368 [<ffffffff830fdcd0>] dummy_timer+0x11f0/0x36d0 drivers/usb/gadget/udc/dummy_hcd.c:1858 [<ffffffff814807c1>] call_timer_fn+0x241/0x800 kernel/time/timer.c:1308 [< inline >] expire_timers kernel/time/timer.c:1348 [<ffffffff81482de6>] __run_timers+0xa06/0xec0 kernel/time/timer.c:1641 [<ffffffff814832c1>] run_timer_softirq+0x21/0x80 kernel/time/timer.c:1654 [<ffffffff84f4af8b>] __do_softirq+0x2fb/0xb63 kernel/softirq.c:284 The cause of the bug is subtle. The dev_config() routine gets called twice by the fuzzer. The first time, the user data contains both a full-speed configuration descriptor and a high-speed config descriptor, causing dev->hs_config to be set. But it also contains an invalid device descriptor, so the buffer containing the descriptors is deallocated and dev_config() returns an error. The second time dev_config() is called, the user data contains only a full-speed config descriptor. But dev->hs_config still has the stale pointer remaining from the first call, causing the routine to think that there is a valid high-speed config. Later on, when the driver dereferences the stale pointer to copy that descriptor, we get a use-after-free access. The fix is simple: Clear dev->hs_config if the passed-in data does not contain a high-speed config descriptor. 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.