Message-ID: <5ae45813.3235.194db3d35f5.Coremail.stitch@zju.edu.cn>
Date: Thu, 6 Feb 2025 20:30:09 +0800 (GMT+08:00)
From: "Jiacheng Xu" <stitch@....edu.cn>
To: andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org
Cc: wolffd@...p.nus.edu.sg
Subject: [BUG] KASAN: slab-use-after-free in slip_open

Hi developers:

We are reporting a Linux issue using a modified version of Syzkaller.

HEAD commit: 4bbf9020 6.13.0-rc4
git tree: upstream
kernel config: https://github.com/google/syzkaller/blob/master/dashboard/config/linux/upstream-apparmor-kasan.config
syz repro: https://drive.google.com/file/d/1XV9WHwMvK4eZIPuyjiWoTpyQ0FpDaUpT/view?usp=sharing
C reproducer: As this is a race condition, a stable C reproducer is not available yet.

Environment:
Ubuntu 22.04 on Linux 5.15
QEMU emulator version 6.2.0
qemu-system-x86_64 \
-m 2G \
-smp 2 \
-kernel /home/wd/bzImage \
-append "console=ttyS0 root=/dev/sda earlyprintk=serial net.ifnames=0" \
-drive file=/home/wd/bullseye.img,format=raw \
-net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \
-net nic,model=e1000 \
-enable-kvm \
-nographic \
-pidfile vm.pid \
2>&1 | tee vm.log

Steps to reproduce:
1. Setup a vm on given kernel.
2. Execute the syz reproducer with `./syz-execprog -executor=./syz-executor -repeat=20000 -procs=8 -cover=0 ~/repro.prog`

Description:
The SLIP driver suffers from a Use-After-Free issue in sl_sync() due to unsynchronized access to net_device pointers stored in slip_devs[]. When a device is being freed (for example, via tty_release()/netdev_run_todo()), sl_sync() may access it after it has been freed.

Patch:
We try to write a patch for the crash. And after applying the patch, the crash can no longer be triggered with the PoC.

--- slip.c      2025-02-06 12:26:25.690890378 +0000
+++ slip.c      2025-02-06 12:29:30.554820899 +0000
@@ -721,8 +721,9 @@
        struct net_device *dev;
        struct slip       *sl;

+       rcu_read_lock();
        for (i = 0; i < slip_maxdev; i++) {
-               dev = slip_devs[i];
+               dev = rcu_dereference(slip_devs[i]);
                if (dev == NULL)
                        break;

@@ -732,6 +733,7 @@
                if (dev->flags & IFF_UP)
                        dev_close(dev);
        }
+       rcu_read_unlock();
 }


If you fix this issue, please add the following tag to the commit:
Reported-by: Jiacheng Xu <stitch@....edu.cn>, Dylan Wolff <wolffd@...p.nus.edu.sg>
==================================================================
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+0x293/0x1330 drivers/net/slip/slip.c:806
Read of size 4 at addr ffff88805cfca0b0 by task syz-executor.2/46673


CPU: 0 UID: 0 PID: 46673 Comm: syz-executor.2 Not tainted 6.13.0-rc4 #2


Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014

Sched_ext: serialise (enabled+all), task: runnable_at=-30ms
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x229/0x350 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x164/0x530 mm/kasan/report.c:489
 kasan_report+0x147/0x180 mm/kasan/report.c:602
 sl_sync drivers/net/slip/slip.c:732 [inline]
 slip_open+0x293/0x1330 drivers/net/slip/slip.c:806
 tty_ldisc_open+0xbd/0x120 drivers/tty/tty_ldisc.c:432
 tty_set_ldisc+0x32b/0x5c0 drivers/tty/tty_ldisc.c:563
 tiocsetd+0x126/0x170 drivers/tty/tty_io.c:2439
 tty_ioctl+0xe5c/0x1090 drivers/tty/tty_io.c:2739
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0x266/0x350 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fed56a903ad
Code: c3 e8 a7 2b 00 00 0f 1f 80 00 00 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fed578b20c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fed56bcbf80 RCX: 00007fed56a903ad
RDX: 0000000020000080 RSI: 0000000000005423 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fed578b2640
R13: 000000000000000e R14: 00007fed56a4fc90 R15: 00007fed578aa000
 </TASK>


Allocated by task 46683:


 kasan_save_stack mm/kasan/common.c:47 [inline]

 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0x89/0xa0 mm/kasan/common.c:394
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4298 [inline]
 __kmalloc_node_noprof+0x28c/0x530 mm/slub.c:4304
 __kvmalloc_node_noprof+0x70/0x180 mm/util.c:650
 alloc_netdev_mqs+0xa7/0x1870 net/core/dev.c:11209
 sl_alloc drivers/net/slip/slip.c:756 [inline]
 slip_open+0x483/0x1330 drivers/net/slip/slip.c:817
 tty_ldisc_open+0xbd/0x120 drivers/tty/tty_ldisc.c:432
 tty_set_ldisc+0x32b/0x5c0 drivers/tty/tty_ldisc.c:563
 tiocsetd+0x126/0x170 drivers/tty/tty_io.c:2439
 tty_ioctl+0xe5c/0x1090 drivers/tty/tty_io.c:2739
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0x266/0x350 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f


Freed by task 46682:


 kasan_save_stack mm/kasan/common.c:47 [inline]

 kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:582
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x5a/0x70 mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2353 [inline]
 slab_free mm/slub.c:4613 [inline]
 kfree+0x196/0x450 mm/slub.c:4761
 device_release+0xcd/0x240
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x248/0x490 lib/kobject.c:737
 netdev_run_todo+0x10e0/0x1280 net/core/dev.c:10924
 tty_ldisc_kill+0xbf/0x150 drivers/tty/tty_ldisc.c:613
 tty_ldisc_release+0x1ae/0x210 drivers/tty/tty_ldisc.c:781
 tty_release_struct+0x2a/0x100 drivers/tty/tty_io.c:1690
 tty_release+0xe4d/0x1460 drivers/tty/tty_io.c:1861
 __fput+0x2ba/0xa80 fs/file_table.c:450
 __fput_sync+0x180/0x1e0 fs/file_table.c:535
 __do_sys_close fs/open.c:1554 [inline]
 __se_sys_close fs/open.c:1539 [inline]
 __x64_sys_close+0x93/0x120 fs/open.c:1539
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf6/0x210 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f


The buggy address belongs to the object at ffff88805cfca000


 which belongs to the cache kmalloc-cg-4k of size 4096

The buggy address is located 176 bytes inside of
 freed 4096-byte region [ffff88805cfca000, ffff88805cfcb000)


The buggy address belongs to the physical page:


page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5cfc8

head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888075c64a01
flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000040 ffff88801d44f500 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000040004 00000001f5000000 ffff888075c64a01
head: 04fff00000000040 ffff88801d44f500 dead000000000100 dead000000000122
head: 0000000000000000 0000000000040004 00000001f5000000 ffff888075c64a01
head: 04fff00000000003 ffffea000173f201 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 9660, tgid 9660 (syz-executor.1), ts 93383578089, free_ts 93076565836
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f6/0x240 mm/page_alloc.c:1558
 prep_new_page mm/page_alloc.c:1566 [inline]
 get_page_from_freelist+0x3586/0x36d0 mm/page_alloc.c:3476
 __alloc_pages_noprof+0x260/0x680 mm/page_alloc.c:4753
 alloc_pages_mpol_noprof+0x3c8/0x650 mm/mempolicy.c:2269
 alloc_slab_page+0x6a/0x110 mm/slub.c:2423
 allocate_slab+0x5f/0x2b0 mm/slub.c:2589
 new_slab mm/slub.c:2642 [inline]
 ___slab_alloc+0xbdf/0x1490 mm/slub.c:3830
 __slab_alloc mm/slub.c:3920 [inline]
 __slab_alloc_node mm/slub.c:3995 [inline]
 slab_alloc_node mm/slub.c:4156 [inline]
 __do_kmalloc_node mm/slub.c:4297 [inline]
 __kmalloc_node_track_caller_noprof+0x30f/0x520 mm/slub.c:4317
 kmemdup_noprof+0x2b/0x60 mm/util.c:135
 __addrconf_sysctl_register+0xb1/0x430 net/ipv6/addrconf.c:7221
 addrconf_sysctl_register+0x1bd/0x220 net/ipv6/addrconf.c:7287
 ipv6_add_dev+0xe13/0x13e0 net/ipv6/addrconf.c:456
 addrconf_notify+0x6d8/0x1170 net/ipv6/addrconf.c:3674
 notifier_call_chain+0x1c6/0x410 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2034 [inline]
 call_netdevice_notifiers+0xd3/0x110 net/core/dev.c:2048
 register_netdevice+0x190c/0x1da0 net/core/dev.c:10632
page last free pid 100 tgid 100 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 free_unref_folios+0xe03/0x1860 mm/page_alloc.c:2706
 shrink_folio_list+0x4698/0x5c80 mm/vmscan.c:1483
 evict_folios+0x3b12/0x5610 mm/vmscan.c:4593
 try_to_shrink_lruvec+0x941/0xc10 mm/vmscan.c:4789
 shrink_one+0x20e/0x870 mm/vmscan.c:4834
 shrink_many mm/vmscan.c:4897 [inline]
 lru_gen_shrink_node mm/vmscan.c:4975 [inline]
 shrink_node+0x3862/0x3f20 mm/vmscan.c:5956
 kswapd_shrink_node mm/vmscan.c:6785 [inline]
 balance_pgdat mm/vmscan.c:6977 [inline]
 kswapd+0x1c9f/0x36f0 mm/vmscan.c:7246
 kthread+0x2c3/0x360 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244


Memory state around the buggy address:


 ffff88805cfc9f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

 ffff88805cfca000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88805cfca080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                     ^
 ffff88805cfca100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88805cfca180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Hi developers:


We are reporting a Linux issue using a modified version of Syzkaller.


HEAD commit: 4bbf9020 6.13.0-rc4

git tree: upstream
kernel config: https://github.com/google/syzkaller/blob/master/dashboard/config/linux/upstream-apparmor-kasan.config
syz repro: https://drive.google.com/file/d/1XV9WHwMvK4eZIPuyjiWoTpyQ0FpDaUpT/view?usp=sharing
C reproducer: As this is a race condition, we cannot obtain a stable C reproducer.


Description:

The SLIP driver suffers from a concurrent Use-After-Free issue in sl_sync() due to
unsynchronized access to net_device pointers stored in slip_devs[]. When a
device is being freed (for example, via tty_release()/netdev_run_todo()),
sl_sync() may access it after it has been freed.

Steps to reproducer:

1. Setup a vm on the given kernel.
2. Use syzkaller to run syz repro with `./syz-execprog -executor=./syz-executor -repeat=20000 -procs=8 -cover=0 ~/repro.prog`.


Environment:

Ubuntu 22.04 on Linux 5.15
QEMU emulator version 6.2.0
qemu-system-x86_64 \
-m 2G \
-smp 2 \
-kernel /home/wd/bzImage \
-append "console=ttyS0 root=/dev/sda earlyprintk=serial net.ifnames=0" \
-drive file=/home/wd/bullseye.img,format=raw \
-net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \
-net nic,model=e1000 \
-enable-kvm \
-nographic \
-pidfile vm.pid \
2>&1 | tee vm.log

If you fix this issue, please add the following tag to the commit:

Reported-by: Jiacheng Xu <stitch@....edu.cn>

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