Re: net/kcm: use-after-free in kcm_wq

On Fri, Mar 3, 2017 at 2:11 AM, Dmitry Vyukov [off-list ref] wrote:

Also like this one:

==================================================================
BUG: KASAN: use-after-free in atomic_long_read
include/linux/compiler.h:254 [inline] at addr ffff8800538aba60
BUG: KASAN: use-after-free in get_work_pool+0x2f2/0x340
kernel/workqueue.c:709 at addr ffff8800538aba60
Read of size 8 by task syz-executor6/7965
CPU: 2 PID: 7965 Comm: syz-executor6 Not tainted 4.10.0+ #248
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:15 [inline]
 dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
 kasan_object_err+0x1c/0x70 mm/kasan/report.c:166
 print_address_description mm/kasan/report.c:204 [inline]
 kasan_report_error mm/kasan/report.c:288 [inline]
 kasan_report.part.2+0x198/0x440 mm/kasan/report.c:310
 kasan_report mm/kasan/report.c:331 [inline]
 __asan_report_load8_noabort+0x29/0x30 mm/kasan/report.c:331
 atomic_long_read include/linux/compiler.h:254 [inline]
 get_work_pool+0x2f2/0x340 kernel/workqueue.c:709
 __queue_work+0x2b3/0x1210 kernel/workqueue.c:1401
 queue_work_on+0x2e9/0x330 kernel/workqueue.c:1486
 queue_work include/linux/workqueue.h:487 [inline]
 strp_check_rcv+0x25/0x30 net/strparser/strparser.c:494

It is not kcm_wq, it is strp_wq, and the work struct is strp->rx_work
which lives in struct kcm_psock. The work is cancelled by strp_done(),
it seems get queued again after strp_done()...

 kcm_attach net/kcm/kcmsock.c:1434 [inline]
 kcm_attach_ioctl net/kcm/kcmsock.c:1455 [inline]
 kcm_ioctl+0x8bb/0x1800 net/kcm/kcmsock.c:1690
 sock_do_ioctl+0x65/0xb0 net/socket.c:895
 sock_ioctl+0x2c2/0x440 net/socket.c:993
 vfs_ioctl fs/ioctl.c:43 [inline]
 do_vfs_ioctl+0x1bf/0x1790 fs/ioctl.c:683
 SYSC_ioctl fs/ioctl.c:698 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x4458d9
RSP: 002b:00007f1dce9d1b58 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000024 RCX: 00000000004458d9
RDX: 0000000020b68000 RSI: 00000000000089e0 RDI: 0000000000000024
RBP: 00000000006e0220 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000007080a8
R13: 0000000000000000 R14: 00007f1dce9d29c0 R15: 00007f1dce9d2700
Object at ffff8800538ab940, in cache kcm_psock_cache size: 616
Allocated:
PID = 7965
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:502
 set_track mm/kasan/kasan.c:514 [inline]
 kasan_kmalloc+0xaa/0xd0 mm/kasan/kasan.c:605
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:544
 kmem_cache_alloc+0x102/0x680 mm/slab.c:3571
 kmem_cache_zalloc include/linux/slab.h:653 [inline]
 kcm_attach net/kcm/kcmsock.c:1384 [inline]
 kcm_attach_ioctl net/kcm/kcmsock.c:1455 [inline]
 kcm_ioctl+0x303/0x1800 net/kcm/kcmsock.c:1690
 sock_do_ioctl+0x65/0xb0 net/socket.c:895
 sock_ioctl+0x2c2/0x440 net/socket.c:993
 vfs_ioctl fs/ioctl.c:43 [inline]
 do_vfs_ioctl+0x1bf/0x1790 fs/ioctl.c:683
 SYSC_ioctl fs/ioctl.c:698 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
 entry_SYSCALL_64_fastpath+0x1f/0xc2
Freed:
PID = 7982
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
 save_stack+0x43/0xd0 mm/kasan/kasan.c:502
 set_track mm/kasan/kasan.c:514 [inline]
 kasan_slab_free+0x6f/0xb0 mm/kasan/kasan.c:578
 __cache_free mm/slab.c:3513 [inline]
 kmem_cache_free+0x71/0x240 mm/slab.c:3773
 kcm_unattach+0xee7/0x1520 net/kcm/kcmsock.c:1558
 kcm_unattach_ioctl net/kcm/kcmsock.c:1603 [inline]
 kcm_ioctl+0xfae/0x1800 net/kcm/kcmsock.c:1700
 sock_do_ioctl+0x65/0xb0 net/socket.c:895
 sock_ioctl+0x2c2/0x440 net/socket.c:993
 vfs_ioctl fs/ioctl.c:43 [inline]
 do_vfs_ioctl+0x1bf/0x1790 fs/ioctl.c:683
 SYSC_ioctl fs/ioctl.c:698 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
 entry_SYSCALL_64_fastpath+0x1f/0xc2
Memory state around the buggy address:
 ffff8800538ab900: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
 ffff8800538ab980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

quoted

ffff8800538aba00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

                                                       ^
 ffff8800538aba80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8800538abb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================