We report a bug (in linux-5.8.13) found by FuzzUSB (a modified version of syzkaller). (corrected analysis) This bug happens while continuing a delayed setup message in mass storage gadget. To be specific, composite_setup() sets FSG_STATE_CONFIG_CHANGE via fsg_set_alt() (line 1793), and followed by cdev->delayed_status++ (line 1798). Meanwile, the mass gadget tries check cdev->delayed_status == 0 through handle_exception() (line 2428), which occurs in between the two operations above. Such a race causes invalid operations eventually. ================================================================== usb_composite_setup_continue: Unexpected call WARNING: CPU: 1 PID: 1882 at drivers/usb/gadget/composite.c:2457 usb_composite_setup_continue+0x1c7/0x220 drivers/usb/gadget/composite.c:2457 Kernel panic - not syncing: panic_on_warn set ... CPU: 1 PID: 1882 Comm: file-storage Not tainted 5.8.13 #4 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0xa7/0xea lib/dump_stack.c:118 panic+0x298/0x521 kernel/panic.c:231 __warn.cold.12+0x25/0x32 kernel/panic.c:600 report_bug+0x1b2/0x260 lib/bug.c:198 handle_bug+0x43/0x70 arch/x86/kernel/traps.c:235 exc_invalid_op+0x18/0x40 arch/x86/kernel/traps.c:255 asm_exc_invalid_op+0x12/0x20 ./arch/x86/include/asm/idtentry.h:540 RIP: 0010:usb_composite_setup_continue+0x1c7/0x220 drivers/usb/gadget/composite.c:2457 Code: 62 48 8b 7b 58 4c 89 fe e8 66 fb ff ff e9 e6 fe ff ff e8 6c 89 87 fd 48 c7 c6 60 c9 41 86 48 c7 c7 60 c6 41 86 e8 78 0c 5c fd <0f> 0b e9 c7 fe ff ff e8 3d a4 ae fd e9 a3 fe ff ff e8 53 a4 ae fd RSP: 0000:ffff8880446dfd38 EFLAGS: 00010086 RAX: 0000000000000000 RBX: ffff888069eee4b0 RCX: 0000000000000000 RDX: 0000000000000027 RSI: 0000000000000004 RDI: ffffed10088dbf9d RBP: ffff8880446dfd60 R08: ffffed100d953fd2 R09: ffffed100d953fd2 R10: ffff88806ca9fe8b R11: ffffed100d953fd1 R12: 0000000000000000 R13: ffff888069eee540 R14: 0000000000000246 R15: ffff888040609310 handle_exception drivers/usb/gadget/function/f_mass_storage.c:2428 [inline] fsg_main_thread+0x12f4/0x59f1 drivers/usb/gadget/function/f_mass_storage.c:2466 kthread+0x374/0x480 kernel/kthread.c:291 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293 Dumping ftrace buffer: (ftrace buffer empty) Kernel Offset: disabled ================================================================== Regards, Kyungtae Kim On Mon, Nov 9, 2020 at 2:08 PM Kyungtae Kim <kt0755@xxxxxxxxx> wrote: > > We report a bug (in linux-5.8.13) found by FuzzUSB (a modified version > of syzkaller). > > The bug happens when the freed object tty->port is accessed in > tty_init_dev (line 1358). > It seems tty->port is freed during the locking (i.e., tty_ldisc_lock) > ahead (line 1355). > > ================================================================== > usb_composite_setup_continue: Unexpected call > WARNING: CPU: 1 PID: 1882 at drivers/usb/gadget/composite.c:2457 usb_composite_setup_continue+0x1c7/0x220 drivers/usb/gadget/composite.c:2457 > Kernel panic - not syncing: panic_on_warn set ... > CPU: 1 PID: 1882 Comm: file-storage Not tainted 5.8.13 #4 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0xa7/0xea lib/dump_stack.c:118 > panic+0x298/0x521 kernel/panic.c:231 > __warn.cold.12+0x25/0x32 kernel/panic.c:600 > report_bug+0x1b2/0x260 lib/bug.c:198 > handle_bug+0x43/0x70 arch/x86/kernel/traps.c:235 > exc_invalid_op+0x18/0x40 arch/x86/kernel/traps.c:255 > asm_exc_invalid_op+0x12/0x20 ./arch/x86/include/asm/idtentry.h:540 > RIP: 0010:usb_composite_setup_continue+0x1c7/0x220 drivers/usb/gadget/composite.c:2457 > Code: 62 48 8b 7b 58 4c 89 fe e8 66 fb ff ff e9 e6 fe ff ff e8 6c 89 87 fd 48 c7 c6 60 c9 41 86 48 c7 c7 60 c6 41 86 e8 78 0c 5c fd <0f> 0b e9 c7 fe ff ff e8 3d a4 ae fd e9 a3 fe ff ff e8 53 a4 ae fd > RSP: 0000:ffff8880446dfd38 EFLAGS: 00010086 > RAX: 0000000000000000 RBX: ffff888069eee4b0 RCX: 0000000000000000 > RDX: 0000000000000027 RSI: 0000000000000004 RDI: ffffed10088dbf9d > RBP: ffff8880446dfd60 R08: ffffed100d953fd2 R09: ffffed100d953fd2 > R10: ffff88806ca9fe8b R11: ffffed100d953fd1 R12: 0000000000000000 > R13: ffff888069eee540 R14: 0000000000000246 R15: ffff888040609310 > handle_exception drivers/usb/gadget/function/f_mass_storage.c:2428 [inline] > fsg_main_thread+0x12f4/0x59f1 drivers/usb/gadget/function/f_mass_storage.c:2466 > kthread+0x374/0x480 kernel/kthread.c:291 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293 > Dumping ftrace buffer: > (ftrace buffer empty) > Kernel Offset: disabled > ================================================================== > > Regards, > Kyungtae Kim
