================================================================== 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 ==================================================================
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] } } ```
I found this bug with a custom syzkaller, but failed to reproduce it as it is a race condition vulnerability, so my analysis may be wrong.
(In reply to j51569436 from comment #2) > I found this bug with a custom syzkaller What do you mean by custom? Do you have some additional syscall/ioctl definitions?
Yes. I added a few syscalls to fuzz the tty ldisc.