Hi,
<[email protected]> reported on Bugzilla race bug on SLIP driver, which is
found with syzkaller [1].
[1]: https://bugzilla.kernel.org/show_bug.cgi?id=218713
The full stack trace was:
> ==================================================================
> BUG: KASAN: slab-use-after-free in sl_sync drivers/net/slip/slip.c:732 [inline]
> BUG: KASAN: slab-use-after-free in slip_open+0xed9/0x1210 drivers/net/slip/slip.c:806
> Read of size 4 at addr ffff88801a5fa0a8 by task syz-executor.1/296035
>
> CPU: 0 PID: 296035 Comm: syz-executor.1 Not tainted 6.8.0-rc5-dirty #283
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:88 [inline]
> dump_stack_lvl+0x37/0x50 lib/dump_stack.c:106
> print_address_description mm/kasan/report.c:377 [inline]
> print_report+0xc1/0x5e0 mm/kasan/report.c:488
> kasan_report+0xb0/0xe0 mm/kasan/report.c:601
> sl_sync drivers/net/slip/slip.c:732 [inline]
> slip_open+0xed9/0x1210 drivers/net/slip/slip.c:806
> tty_ldisc_open+0x9f/0x120 drivers/tty/tty_ldisc.c:432
> tty_set_ldisc+0x2e7/0x680 drivers/tty/tty_ldisc.c:557
> tiocsetd drivers/tty/tty_io.c:2439 [inline]
> tty_ioctl+0x5c0/0x1590 drivers/tty/tty_io.c:2739
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:871 [inline]
> __se_sys_ioctl fs/ioctl.c:857 [inline]
> __x64_sys_ioctl+0x12d/0x1a0 fs/ioctl.c:857
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xc0/0x250 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x6f/0x77
> RIP: 0033:0x7fc365c9128f
> Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 77 1f 48 8b 44 24 18 64 48 2b 04 25 28 00
> RSP: 002b:00007fc366a68f90 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 0000006900000000 RCX: 00007fc365c9128f
> RDX: 00007fc366a68ff4 RSI: 0000000000005423 RDI: 000000000000006a
> RBP: 000000000000006a R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000b R14: 00007fc365dee040 R15: 00007fc366a49000
> </TASK>
>
> Allocated by task 296005:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:47
> kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> poison_kmalloc_redzone mm/kasan/common.c:372 [inline]
> __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:389
> kasan_kmalloc include/linux/kasan.h:211 [inline]
> __do_kmalloc_node mm/slub.c:3981 [inline]
> __kmalloc_node+0x208/0x540 mm/slub.c:3988
> kvmalloc include/linux/slab.h:728 [inline]
> kvzalloc include/linux/slab.h:736 [inline]
> alloc_netdev_mqs+0x5f/0x11d0 net/core/dev.c:10826
> sl_alloc drivers/net/slip/slip.c:756 [inline]
> slip_open+0x371/0x1210 drivers/net/slip/slip.c:817
> tty_ldisc_open+0x9f/0x120 drivers/tty/tty_ldisc.c:432
> tty_set_ldisc+0x2e7/0x680 drivers/tty/tty_ldisc.c:557
> tiocsetd drivers/tty/tty_io.c:2439 [inline]
> tty_ioctl+0x5c0/0x1590 drivers/tty/tty_io.c:2739
> vfs_ioctl fs/ioctl.c:51 [inline]
> __do_sys_ioctl fs/ioctl.c:871 [inline]
> __se_sys_ioctl fs/ioctl.c:857 [inline]
> __x64_sys_ioctl+0x12d/0x1a0 fs/ioctl.c:857
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xc0/0x250 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x6f/0x77
>
> Freed by task 296004:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:47
> kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> kasan_save_free_info+0x3f/0x60 mm/kasan/generic.c:640
> poison_slab_object mm/kasan/common.c:241 [inline]
> poison_slab_object+0x102/0x190 mm/kasan/common.c:212
> __kasan_slab_free+0x37/0x80 mm/kasan/common.c:257
> kasan_slab_free include/linux/kasan.h:184 [inline]
> slab_free_hook mm/slub.c:2121 [inline]
> slab_free mm/slub.c:4299 [inline]
> kfree+0xfb/0x350 mm/slub.c:4409
> device_release+0x97/0x210 drivers/base/core.c:2499
> kobject_cleanup lib/kobject.c:689 [inline]
> kobject_release lib/kobject.c:720 [inline]
> kref_put include/linux/kref.h:65 [inline]
> kobject_put+0x143/0x3f0 lib/kobject.c:737
> netdev_run_todo+0x535/0xd40 net/core/dev.c:10581
> slip_close drivers/net/slip/slip.c:906 [inline]
> slip_hangup+0x165/0x1c0 drivers/net/slip/slip.c:912
> tty_ldisc_hangup+0x1dd/0x700 drivers/tty/tty_ldisc.c:699
> __tty_hangup.part.0+0x4d4/0x9b0 drivers/tty/tty_io.c:630
> __tty_hangup drivers/tty/tty_io.c:585 [inline]
> tty_vhangup+0x21/0x30 drivers/tty/tty_io.c:700
> pty_close+0x3a3/0x4f0 drivers/tty/pty.c:79
> tty_release+0x3a2/0x1390 drivers/tty/tty_io.c:1760
> __fput+0x1fb/0xa90 fs/file_table.c:376
> __do_sys_close fs/open.c:1554 [inline]
> __se_sys_close fs/open.c:1539 [inline]
> __x64_sys_close+0x78/0xd0 fs/open.c:1539
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xc0/0x250 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x6f/0x77
>
> The buggy address belongs to the object at ffff88801a5fa000
> which belongs to the cache kmalloc-cg-4k of size 4096
> The buggy address is located 168 bytes inside of
> freed 4096-byte region [ffff88801a5fa000, ffff88801a5fb000)
>
> The buggy address belongs to the physical page:
> page:ffffea0000697e00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1a5f8
> head:ffffea0000697e00 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> memcg:ffff888026f825c1
> flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
> page_type: 0xffffffff()
> raw: 00fff00000000840 ffff888010c4e500 ffffea00005eb600 0000000000000002
> raw: 0000000000000000 0000000000040004 00000001ffffffff ffff888026f825c1
> page dumped because: kasan: bad access detected
> page_owner tracks the page as allocated
> page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 5568, tgid 5568 (systemd-udevd), ts 937169338299, free_ts 937110171114
> set_page_owner include/linux/page_owner.h:31 [inline]
> post_alloc_hook+0x2dd/0x350 mm/page_alloc.c:1533
> prep_new_page mm/page_alloc.c:1540 [inline]
> get_page_from_freelist+0xd0a/0x3570 mm/page_alloc.c:3311
> __alloc_pages+0x21f/0x1f30 mm/page_alloc.c:4567
> __alloc_pages_node include/linux/gfp.h:238 [inline]
> alloc_pages_node include/linux/gfp.h:261 [inline]
> alloc_slab_page mm/slub.c:2190 [inline]
> allocate_slab mm/slub.c:2354 [inline]
> new_slab+0xd3/0x3b0 mm/slub.c:2407
> ___slab_alloc+0x679/0xba0 mm/slub.c:3540
> __slab_alloc mm/slub.c:3625 [inline]
> __slab_alloc_node mm/slub.c:3678 [inline]
> slab_alloc_node mm/slub.c:3850 [inline]
> __do_kmalloc_node mm/slub.c:3980 [inline]
> __kmalloc_node+0x39e/0x540 mm/slub.c:3988
> kvmalloc include/linux/slab.h:728 [inline]
> seq_buf_alloc fs/seq_file.c:38 [inline]
> seq_read_iter+0x6b0/0x10c0 fs/seq_file.c:210
> call_read_iter include/linux/fs.h:2079 [inline]
> new_sync_read fs/read_write.c:395 [inline]
> vfs_read+0x4e9/0x8c0 fs/read_write.c:476
> ksys_read+0xec/0x1c0 fs/read_write.c:619
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xc0/0x250 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x6f/0x77
> page last free pid 0 tgid 0 stack trace:
> reset_page_owner include/linux/page_owner.h:24 [inline]
> free_pages_prepare mm/page_alloc.c:1140 [inline]
> free_unref_page_prepare+0x5b8/0xbd0 mm/page_alloc.c:2346
> free_unref_page+0x33/0x360 mm/page_alloc.c:2486
> rcu_do_batch kernel/rcu/tree.c:2190 [inline]
> rcu_core+0xe20/0x1930 kernel/rcu/tree.c:2465
> __do_softirq+0x1a2/0x629 kernel/softirq.c:553
>
> Memory state around the buggy address:
> ffff88801a5f9f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88801a5fa000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff88801a5fa080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff88801a5fa100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88801a5fa180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
He also posted C reproducers:
> slip_open calls sl_sync.
>
> ```c
> static int slip_open(struct tty_struct *tty)
> {
> struct slip *sl;
> int err;
>
> if (!capable(CAP_NET_ADMIN))
> return -EPERM;
>
> if (tty->ops->write == NULL)
> return -EOPNOTSUPP;
>
> /* RTnetlink lock is misused here to serialize concurrent
> opens of slip channels. There are better ways, but it is
> the simplest one.
> */
> rtnl_lock();
>
> /* Collect hanged up channels. */
> sl_sync();
> ...
>
> ```
>
> sl_sync declares the dev variable by referencing the global variable slip_devs. There is no lock to safely access the global variable.
>
> ```c
>
> /* Collect hanged up channels */
> static void sl_sync(void)
> {
> int i;
> struct net_device *dev;
> struct slip *sl;
>
> for (i = 0; i < slip_maxdev; i++) {
> dev = slip_devs[i];
> if (dev == NULL)
> break;
>
> sl = netdev_priv(dev);
> if (sl->tty || sl->leased)//[1]
> continue;
> if (dev->flags & IFF_UP)
> dev_close(dev);
> }
> }
> ```
>
>
> slip_close call netdev_run_todo.
> [1] : call __rtnl_unlock
> [2] : call sl_free_netdev. sl_free_netdev set slip_devs[i] to NULL;
> [3] : free slip_devs[i]
> ```c
> void netdev_run_todo(void)
> {
> struct net_device *dev, *tmp;
> struct list_head list;
> #ifdef CONFIG_LOCKDEP
> struct list_head unlink_list;
>
> list_replace_init(&net_unlink_list, &unlink_list);
>
> while (!list_empty(&unlink_list)) {
> struct net_device *dev = list_first_entry(&unlink_list,
> struct net_device,
> unlink_list);
> list_del_init(&dev->unlink_list);
> dev->nested_level = dev->lower_level - 1;
> }
> #endif
>
> /* Snapshot list, allow later requests */
> list_replace_init(&net_todo_list, &list);
>
> __rtnl_unlock();//[1]
>
> while (!list_empty(&list)) {
> ...
> if (dev->priv_destructor)//[2]
> dev->priv_destructor(dev);
> if (dev->needs_free_netdev)
> free_netdev(dev);
>
> if (atomic_dec_and_test(&dev_net(dev)->dev_unreg_count))
> wake_up(&netdev_unregistering_wq);
>
> /* Free network device */
> kobject_put(&dev->dev.kobj);//[3]
> }
> }
> ```
Thanks.
--
An old man doll... just what I always wanted! - Clara