Re: WARNING in usb_composite_setup_continue

Kyungtae Kim
2020-11-09T19:30:00Z

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@gmail.com> 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