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A NULL-pointer dereference bug in gadgetfs was uncovered by syzkaller: > kasan: GPF could be caused by NULL-ptr deref or user memory access > general protection fault: 0000 [#1] SMP KASAN > Dumping ftrace buffer: > (ftrace buffer empty) > Modules linked in: > CPU: 2 PID: 4820 Comm: syz-executor0 Not tainted 4.12.0-rc4+ #5 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > task: ffff880039542dc0 task.stack: ffff88003bdd0000 > RIP: 0010:__list_del_entry_valid+0x7e/0x170 lib/list_debug.c:51 > RSP: 0018:ffff88003bdd6e50 EFLAGS: 00010246 > RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000010000 > RDX: 0000000000000000 RSI: ffffffff86504948 RDI: ffffffff86504950 > RBP: ffff88003bdd6e68 R08: ffff880039542dc0 R09: ffffffff8778ce00 > R10: ffff88003bdd6e68 R11: dffffc0000000000 R12: 0000000000000000 > R13: dffffc0000000000 R14: 1ffff100077badd2 R15: ffffffff864d2e40 > FS: 0000000000000000(0000) GS:ffff88006dc00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 000000002014aff9 CR3: 0000000006022000 CR4: 00000000000006e0 > Call Trace: > __list_del_entry include/linux/list.h:116 [inline] > list_del include/linux/list.h:124 [inline] > usb_gadget_unregister_driver+0x166/0x4c0 drivers/usb/gadget/udc/core.c:1387 > dev_release+0x80/0x160 drivers/usb/gadget/legacy/inode.c:1187 > __fput+0x332/0x7f0 fs/file_table.c:209 > ____fput+0x15/0x20 fs/file_table.c:245 > task_work_run+0x19b/0x270 kernel/task_work.c:116 > exit_task_work include/linux/task_work.h:21 [inline] > do_exit+0x18a3/0x2820 kernel/exit.c:878 > do_group_exit+0x149/0x420 kernel/exit.c:982 > get_signal+0x77f/0x1780 kernel/signal.c:2318 > do_signal+0xd2/0x2130 arch/x86/kernel/signal.c:808 > exit_to_usermode_loop+0x1a7/0x240 arch/x86/entry/common.c:157 > prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline] > syscall_return_slowpath+0x3ba/0x410 arch/x86/entry/common.c:263 > entry_SYSCALL_64_fastpath+0xbc/0xbe > RIP: 0033:0x4461f9 > RSP: 002b:00007fdac2b1ecf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca > RAX: fffffffffffffe00 RBX: 00000000007080c8 RCX: 00000000004461f9 > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000007080c8 > RBP: 00000000007080a8 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > R13: 0000000000000000 R14: 00007fdac2b1f9c0 R15: 00007fdac2b1f700 > Code: 00 00 00 00 ad de 49 39 c4 74 6a 48 b8 00 02 00 00 00 00 ad de > 48 89 da 48 39 c3 74 74 48 c1 ea 03 48 b8 00 00 00 00 00 fc ff df <80> > 3c 02 00 0f 85 92 00 00 00 48 8b 13 48 39 f2 75 66 49 8d 7c > RIP: __list_del_entry_valid+0x7e/0x170 lib/list_debug.c:51 RSP: ffff88003bdd6e50 > ---[ end trace 30e94b1eec4831c8 ]--- > Kernel panic - not syncing: Fatal exception The bug was caused by dev_release() failing to turn off its gadget_registered flag after unregistering the gadget driver. As a result, when a later user closed the device file before writing a valid set of descriptors, dev_release() thought the gadget had been registered and tried to unregister it, even though it had not been. This led to the NULL pointer dereference. The fix is simple: turn off the flag when the gadget is unregistered. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-and-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.