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Date: Thu, 28 Apr 2022 11:19:46 +0800
From: Minh Yuan <yuanmingbuaa@...il.com>
To: oss-security@...ts.openwall.com
Subject: Linux kernel: A concurrency use-after-free in floppy's raw_cmd
Hi,
We recently discovered a concurrency uaf between raw_cmd_ioctl and
seek_interrupt in the latest kernel version (5.17.4 for now).
The root cause is that after deallocating raw_cmd in raw_cmd_ioctl,
seek_interrupt still holds the freed raw_cmd and accesses it in
floppy_ready or start_motor concurrently.
PoC (generated by syzkaller) is in the attachment, and here is the KASAN
report:
BUG: KASAN: use-after-free in start_motor+0x31b/0x3f0
drivers/block/floppy.c:1908
Read of size 4 at addr ffff888127331c00 by task kworker/u16:9/15911
CPU: 5 PID: 15911 Comm: kworker/u16:9 Not tainted 5.16.2 #20
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
Workqueue: floppy floppy_work_workfn
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
print_address_description.constprop.0.cold+0x8d/0x320 mm/kasan/report.c:247
__kasan_report mm/kasan/report.c:433 [inline]
kasan_report.cold+0x83/0xdf mm/kasan/report.c:450
start_motor+0x31b/0x3f0 drivers/block/floppy.c:1908
floppy_ready+0x83/0x1850 drivers/block/floppy.c:1935
seek_interrupt+0x326/0x420 drivers/block/floppy.c:1567
process_one_work+0x9b2/0x1660 kernel/workqueue.c:2317
worker_thread+0x65d/0x1130 kernel/workqueue.c:2465
kthread+0x405/0x4f0 kernel/kthread.c:327
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
Allocated by task 22033:
kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc mm/kasan/common.c:513 [inline]
____kasan_kmalloc mm/kasan/common.c:472 [inline]
__kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:522
kmalloc include/linux/slab.h:590 [inline]
raw_cmd_copyin drivers/block/floppy.c:3100 [inline]
raw_cmd_ioctl drivers/block/floppy.c:3167 [inline]
fd_locked_ioctl+0x100e/0x2820 drivers/block/floppy.c:3535
fd_ioctl+0x35/0x50 drivers/block/floppy.c:3562
blkdev_ioctl+0x37a/0x800 block/ioctl.c:609
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
Freed by task 22033:
kasan_save_stack+0x1e/0x50 mm/kasan/common.c:38
kasan_set_track+0x21/0x30 mm/kasan/common.c:46
kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:370
____kasan_slab_free mm/kasan/common.c:366 [inline]
____kasan_slab_free mm/kasan/common.c:328 [inline]
__kasan_slab_free+0xff/0x130 mm/kasan/common.c:374
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:1723 [inline]
slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1749
slab_free mm/slub.c:3513 [inline]
kfree+0xf6/0x560 mm/slub.c:4561
raw_cmd_free+0x8a/0x1c0 drivers/block/floppy.c:3086
raw_cmd_ioctl drivers/block/floppy.c:3187 [inline]
fd_locked_ioctl+0x206d/0x2820 drivers/block/floppy.c:3535
fd_ioctl+0x35/0x50 drivers/block/floppy.c:3562
blkdev_ioctl+0x37a/0x800 block/ioctl.c:609
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
The new patch can been seen at
https://github.com/torvalds/linux/commit/233087ca063686964a53c829d547c7571e3f67bf
.
Regards,
Yuan Ming from Tsinghua University
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