[syzbot] [nbd?] KASAN: slab-use-after-free Write in recv_work (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 98bd8b16ae57 Add linux-next specific files for 20251031
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16802292580000
kernel config: https://syzkaller.appspot.com/x/.config?x=55e89517f3847929
dashboard link: https://syzkaller.appspot.com/bug?extid=56fbf4c7ddf65e95c7cc
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=152a5012580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=108dee14580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f5d0f0fd772a/disk-98bd8b16.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ead68b596c79/vmlinux-98bd8b16.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6722387b293d/bzImage-98bd8b16.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+56fbf4...@syzkaller.appspotmail.com

block nbd0: Receive control failed (result -32)
block nbd0: shutting down sockets
==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: slab-use-after-free in atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline]
BUG: KASAN: slab-use-after-free in recv_work+0x1b78/0x1c60 drivers/block/nbd.c:1028
Write of size 4 at addr ffff88802f2bee78 by task kworker/u9:1/5145

CPU: 0 UID: 0 PID: 5145 Comm: kworker/u9:1 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: nbd0-recv recv_work
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:200
instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline]
recv_work+0x1b78/0x1c60 drivers/block/nbd.c:1028
process_one_work+0x94a/0x15d0 kernel/workqueue.c:3267
process_scheduled_works kernel/workqueue.c:3350 [inline]
worker_thread+0x9b0/0xee0 kernel/workqueue.c:3431
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 5998:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
poison_kmalloc_redzone mm/kasan/common.c:397 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:414
kasan_kmalloc include/linux/kasan.h:262 [inline]
__kmalloc_cache_noprof+0x3e2/0x700 mm/slub.c:5771
kmalloc_noprof include/linux/slab.h:957 [inline]
kzalloc_noprof include/linux/slab.h:1094 [inline]
nbd_alloc_and_init_config+0x88/0x260 drivers/block/nbd.c:1683
nbd_genl_connect+0x9d7/0x18f0 drivers/block/nbd.c:2145
genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:746
____sys_sendmsg+0x505/0x830 net/socket.c:2634
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2688
__sys_sendmsg net/socket.c:2720 [inline]
__do_sys_sendmsg net/socket.c:2725 [inline]
__se_sys_sendmsg net/socket.c:2723 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2723
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5145:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:252 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284
kasan_slab_free include/linux/kasan.h:234 [inline]
slab_free_hook mm/slub.c:2547 [inline]
slab_free mm/slub.c:6638 [inline]
kfree+0x19a/0x6d0 mm/slub.c:6845
nbd_config_put+0x4a1/0x580 drivers/block/nbd.c:1463
recv_work+0x1b62/0x1c60 drivers/block/nbd.c:1027
process_one_work+0x94a/0x15d0 kernel/workqueue.c:3267
process_scheduled_works kernel/workqueue.c:3350 [inline]
worker_thread+0x9b0/0xee0 kernel/workqueue.c:3431
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff88802f2bee00
which belongs to the cache kmalloc-256 of size 256
The buggy address is located 120 bytes inside of
freed 256-byte region [ffff88802f2bee00, ffff88802f2bef00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2f2be
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b026b40 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b026b40 dead000000000122 0000000000000000
head: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffea0000bcaf81 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5937, tgid 5937 (syz-executor), ts 108999640718, free_ts 108976063617
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3920
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5214
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2479
alloc_slab_page mm/slub.c:3063 [inline]
allocate_slab+0x96/0x350 mm/slub.c:3236
new_slab mm/slub.c:3290 [inline]
___slab_alloc+0xe94/0x18a0 mm/slub.c:4659
__slab_alloc+0x65/0x100 mm/slub.c:4778
__slab_alloc_node mm/slub.c:4854 [inline]
slab_alloc_node mm/slub.c:5276 [inline]
__do_kmalloc_node mm/slub.c:5649 [inline]
__kmalloc_noprof+0x47d/0x800 mm/slub.c:5662
kmalloc_noprof include/linux/slab.h:961 [inline]
kmalloc_array_noprof include/linux/slab.h:1003 [inline]
genl_family_rcv_msg_attrs_parse+0xa3/0x2a0 net/netlink/genetlink.c:940
genl_family_rcv_msg_doit+0xb8/0x300 net/netlink/genetlink.c:1093
genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:746
page last free pid 5937 tgid 5937 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbc8/0xd30 mm/page_alloc.c:2948
__slab_free+0x2e7/0x390 mm/slub.c:5970
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:349
kasan_slab_alloc include/linux/kasan.h:252 [inline]
slab_post_alloc_hook mm/slub.c:4978 [inline]
slab_alloc_node mm/slub.c:5288 [inline]
kmem_cache_alloc_noprof+0x37d/0x700 mm/slub.c:5295
__kernfs_new_node+0xd7/0x7e0 fs/kernfs/dir.c:637
kernfs_new_node+0x102/0x210 fs/kernfs/dir.c:713
__kernfs_create_file+0x4b/0x2e0 fs/kernfs/file.c:1057
sysfs_add_file_mode_ns+0x238/0x300 fs/sysfs/file.c:313
sysfs_merge_group+0x177/0x310 fs/sysfs/group.c:376
dpm_sysfs_add+0xd2/0x270 drivers/base/power/sysfs.c:704
device_add+0x4d8/0xb80 drivers/base/core.c:3649
wiphy_register+0x1d2e/0x2d20 net/wireless/core.c:1035
ieee80211_register_hw+0x34a7/0x4110 net/mac80211/main.c:1591
mac80211_hwsim_new_radio+0x2f85/0x5340 drivers/net/wireless/virtual/mac80211_hwsim.c:5804

Memory state around the buggy address:
ffff88802f2bed00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802f2bed80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802f2bee00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88802f2bee80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88802f2bef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Lizhi Xu]

#syz test

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index a853c65ac65d..215fc18115b7 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1024,9 +1024,9 @@ static void recv_work(struct work_struct *work)
nbd_mark_nsock_dead(nbd, nsock, 1);
mutex_unlock(&nsock->tx_lock);

- nbd_config_put(nbd);
atomic_dec(&config->recv_threads);
wake_up(&config->recv_wq);
+ nbd_config_put(nbd);
kfree(args);
}

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in get_data

------------[ cut here ]------------
WARNING: kernel/printk/printk_ringbuffer.c:1278 at get_data+0x48a/0x840 kernel/printk/printk_ringbuffer.c:1278, CPU#1: syz.0.527/8152
Modules linked in:
CPU: 1 UID: 0 PID: 8152 Comm: syz.0.527 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025

RIP: 0010:get_data+0x48a/0x840 kernel/printk/printk_ringbuffer.c:1278
Code: 83 c4 f8 48 b8 00 00 00 00 00 fc ff df 41 0f b6 04 07 84 c0 0f 85 ee 01 00 00 44 89 65 00 49 83 c5 08 eb 13 e8 b7 d6 1e 00 90 <0f> 0b 90 eb 05 e8 ac d6 1e 00 45 31 ed 4c 89 e8 48 83 c4 28 5b 41
RSP: 0018:ffffc9000d8f6760 EFLAGS: 00010293
RAX: ffffffff81a1ff09 RBX: 00003fffffffffff RCX: ffff888027288000
RDX: 0000000000000000 RSI: 00003fffffffffff RDI: 0000000000000000
RBP: 0000000000000012 R08: 00000000000010f0 R09: 00000030039f1912
R10: 00000030039f1912 R11: 00001fd8c200001e R12: 0000000000000012
R13: 0000000000000000 R14: ffffc9000d8f68a8 R15: 1ffffffff1c4ab06
FS: 00007f678b3656c0(0000) GS:ffff888125b9c000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f678b343f98 CR3: 000000002b512000 CR4: 00000000003526f0
Call Trace:
<TASK>
copy_data kernel/printk/printk_ringbuffer.c:1857 [inline]
prb_read kernel/printk/printk_ringbuffer.c:1966 [inline]
_prb_read_valid+0x672/0xa90 kernel/printk/printk_ringbuffer.c:2143
prb_read_valid+0x3c/0x60 kernel/printk/printk_ringbuffer.c:2215
printk_get_next_message+0x15c/0x7b0 kernel/printk/printk.c:2978
console_emit_next_record kernel/printk/printk.c:3062 [inline]
console_flush_one_record kernel/printk/printk.c:3194 [inline]
console_flush_all+0x4cc/0xb10 kernel/printk/printk.c:3268
__console_flush_and_unlock kernel/printk/printk.c:3298 [inline]
console_unlock+0xbb/0x190 kernel/printk/printk.c:3338
vprintk_emit+0x4c5/0x590 kernel/printk/printk.c:2423
dev_vprintk_emit+0x337/0x3f0 drivers/base/core.c:4914
dev_printk_emit+0xe0/0x130 drivers/base/core.c:4925
_dev_info+0x10a/0x160 drivers/base/core.c:4983
nbd_genl_reconfigure+0x106d/0x1a50 drivers/block/nbd.c:2439

genl_family_rcv_msg_doit+0x215/0x300 net/netlink/genetlink.c:1115
genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
genl_rcv_msg+0x60e/0x790 net/netlink/genetlink.c:1210
netlink_rcv_skb+0x208/0x470 net/netlink/af_netlink.c:2550
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x21c/0x270 net/socket.c:746
____sys_sendmsg+0x505/0x830 net/socket.c:2634
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2688
__sys_sendmsg net/socket.c:2720 [inline]
__do_sys_sendmsg net/socket.c:2725 [inline]
__se_sys_sendmsg net/socket.c:2723 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2723
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f678a58efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f678b365038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f678a7e5fa0 RCX: 00007f678a58efc9
RDX: 0000000000000000 RSI: 00002000000002c0 RDI: 0000000000000008
RBP: 00007f678a611f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f678a7e6038 R14: 00007f678a7e5fa0 R15: 00007fffd7aaf958
</TASK>


Tested on:

commit: 98bd8b16 Add linux-next specific files for 20251031
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15ad4532580000

kernel config: https://syzkaller.appspot.com/x/.config?x=55e89517f3847929
dashboard link: https://syzkaller.appspot.com/bug?extid=56fbf4c7ddf65e95c7cc
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=153ba012580000

[Lizhi Xu]

#syz test

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c

index a853c65ac65d..d5de9bac68f1 100644

--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1024,9 +1024,9 @@ static void recv_work(struct work_struct *work)
nbd_mark_nsock_dead(nbd, nsock, 1);
mutex_unlock(&nsock->tx_lock);

- nbd_config_put(nbd);
atomic_dec(&config->recv_threads);
wake_up(&config->recv_wq);
+ nbd_config_put(nbd);
kfree(args);
}

@@ -1540,7 +1540,10 @@ static int nbd_start_device(struct nbd_device *nbd)
args->index = i;
queue_work(nbd->recv_workq, &args->work);
}
- return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
+ error = nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
+ if (error)
+ flush_workqueue(nbd->recv_workq);
+ return error;
}

static int nbd_start_device_ioctl(struct nbd_device *nbd)
@@ -2355,6 +2358,7 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
}
mutex_unlock(&nbd_index_mutex);

+ mutex_lock(&nbd->config_lock);
config = nbd_get_config_unlocked(nbd);
if (!config) {
dev_err(nbd_to_dev(nbd),
@@ -2363,7 +2367,6 @@ static int nbd_genl_reconfigure(struct sk_buff *skb, struct genl_info *info)
return -EINVAL;
}

- mutex_lock(&nbd->config_lock);
if (!test_bit(NBD_RT_BOUND, &config->runtime_flags) ||
!nbd->pid) {
dev_err(nbd_to_dev(nbd),

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "64" "ARCH=x86_64" "LLVM=1" "bzImage"]: exit status 2


Tested on:

commit: 98231209 Add linux-next specific files for 20251103
git tree: linux-next

kernel config: https://syzkaller.appspot.com/x/.config?x=55e89517f3847929
dashboard link: https://syzkaller.appspot.com/bug?extid=56fbf4c7ddf65e95c7cc
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=169fd704580000

[Lizhi Xu]

[syzbot]

patch: https://syzkaller.appspot.com/x/patch.diff?x=17d41e14580000