Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter

From: syzbot
Date: Thu Mar 27 2025 - 17:19:19 EST

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In reply to: K Prateek Nayak: "Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter"
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Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in p9_conn_cancel

==================================================================
BUG: KASAN: slab-use-after-free in p9_conn_cancel+0x900/0x910 net/9p/trans_fd.c:205
Read of size 8 at addr ffff88807b19ea50 by task syz-executor/6595

CPU: 0 UID: 0 PID: 6595 Comm: syz-executor Not tainted 6.13.0-rc1-syzkaller-00017-gaaec5a95d596-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xc3/0x620 mm/kasan/report.c:489
kasan_report+0xd9/0x110 mm/kasan/report.c:602
p9_conn_cancel+0x900/0x910 net/9p/trans_fd.c:205
p9_conn_destroy net/9p/trans_fd.c:927 [inline]
p9_fd_close+0x3c5/0x590 net/9p/trans_fd.c:951
p9_client_destroy+0xce/0x480 net/9p/client.c:1077
v9fs_session_close+0x49/0x2d0 fs/9p/v9fs.c:506
v9fs_kill_super+0x4d/0xa0 fs/9p/vfs_super.c:196
deactivate_locked_super+0xbe/0x1a0 fs/super.c:473
deactivate_super+0xde/0x100 fs/super.c:506
cleanup_mnt+0x222/0x450 fs/namespace.c:1373
task_work_run+0x14e/0x250 kernel/task_work.c:239
exit_task_work include/linux/task_work.h:43 [inline]
do_exit+0xadd/0x2d70 kernel/exit.c:938
do_group_exit+0xd3/0x2a0 kernel/exit.c:1087
get_signal+0x24ed/0x26c0 kernel/signal.c:3017
arch_do_signal_or_restart+0x90/0x7e0 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x150/0x2a0 kernel/entry/common.c:218
do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa1f978bb7c
Code: Unable to access opcode bytes at 0x7fa1f978bb52.
RSP: 002b:00007ffd5c5893b0 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: fffffffffffffe00 RBX: 0000000000000003 RCX: 00007fa1f978bb7c
RDX: 0000000000000030 RSI: 00007ffd5c589470 RDI: 00000000000000f9
RBP: 00007ffd5c58941c R08: 0000000000000000 R09: 0079746972756365
R10: 00007ffd5c588d70 R11: 0000000000000246 R12: 0000000000000258
R13: 00000000000927c0 R14: 0000000000019c1d R15: 00007ffd5c589470
</TASK>

Allocated by task 52:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
kasan_save_track+0x14/0x30 mm/kasan/common.c:68
unpoison_slab_object mm/kasan/common.c:319 [inline]
__kasan_slab_alloc+0x89/0x90 mm/kasan/common.c:345
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4104 [inline]
slab_alloc_node mm/slub.c:4153 [inline]
kmem_cache_alloc_noprof+0x226/0x3d0 mm/slub.c:4160
p9_tag_alloc+0x9c/0x870 net/9p/client.c:281
p9_client_prepare_req+0x19f/0x4d0 net/9p/client.c:644
p9_client_rpc+0x1c3/0xc10 net/9p/client.c:691
p9_client_write+0x31f/0x680 net/9p/client.c:1645
v9fs_issue_write+0xe2/0x180 fs/9p/vfs_addr.c:59
netfs_do_issue_write+0x92/0x110 fs/netfs/write_issue.c:233
netfs_retry_write_stream fs/netfs/write_collect.c:184 [inline]
netfs_retry_writes fs/netfs/write_collect.c:361 [inline]
netfs_collect_write_results fs/netfs/write_collect.c:529 [inline]
netfs_write_collection_worker+0x3e10/0x47d0 fs/netfs/write_collect.c:551
process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3229
process_scheduled_works kernel/workqueue.c:3310 [inline]
worker_thread+0x6c8/0xf00 kernel/workqueue.c:3391
kthread+0x2c1/0x3a0 kernel/kthread.c:389
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Freed by task 5192:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
kasan_save_track+0x14/0x30 mm/kasan/common.c:68
kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:582
poison_slab_object mm/kasan/common.c:247 [inline]
__kasan_slab_free+0x51/0x70 mm/kasan/common.c:264
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2338 [inline]
slab_free_after_rcu_debug+0x115/0x340 mm/slub.c:4648
rcu_do_batch kernel/rcu/tree.c:2567 [inline]
rcu_core+0x79d/0x14d0 kernel/rcu/tree.c:2823
handle_softirqs+0x213/0x8f0 kernel/softirq.c:554
__do_softirq kernel/softirq.c:588 [inline]
invoke_softirq kernel/softirq.c:428 [inline]
__irq_exit_rcu+0x109/0x170 kernel/softirq.c:655
irq_exit_rcu+0x9/0x30 kernel/softirq.c:671
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1049
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

Last potentially related work creation:
kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
__kasan_record_aux_stack+0xba/0xd0 mm/kasan/generic.c:544
slab_free_hook mm/slub.c:2299 [inline]
slab_free mm/slub.c:4598 [inline]
kmem_cache_free+0x305/0x4c0 mm/slub.c:4700
p9_req_put net/9p/client.c:409 [inline]
p9_req_put+0x1c6/0x250 net/9p/client.c:402
p9_client_rpc+0x591/0xc10 net/9p/client.c:761
p9_client_write+0x31f/0x680 net/9p/client.c:1645
v9fs_issue_write+0xe2/0x180 fs/9p/vfs_addr.c:59
netfs_do_issue_write+0x92/0x110 fs/netfs/write_issue.c:233
netfs_retry_write_stream fs/netfs/write_collect.c:184 [inline]
netfs_retry_writes fs/netfs/write_collect.c:361 [inline]
netfs_collect_write_results fs/netfs/write_collect.c:529 [inline]
netfs_write_collection_worker+0x3e10/0x47d0 fs/netfs/write_collect.c:551
process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3229
process_scheduled_works kernel/workqueue.c:3310 [inline]
worker_thread+0x6c8/0xf00 kernel/workqueue.c:3391
kthread+0x2c1/0x3a0 kernel/kthread.c:389
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

The buggy address belongs to the object at ffff88807b19e990
which belongs to the cache p9_req_t of size 208
The buggy address is located 192 bytes inside of
freed 208-byte region [ffff88807b19e990, ffff88807b19ea60)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7b19e
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88814c7a0140 ffffea0001dd70c0 0000000000000006
raw: 0000000000000000 00000000000f000f 00000001f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 6752, tgid 6751 (syz.0.17), ts 91802565462, free_ts 91788017536
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x2d1/0x350 mm/page_alloc.c:1556
prep_new_page mm/page_alloc.c:1564 [inline]
get_page_from_freelist+0xfce/0x2f80 mm/page_alloc.c:3474
__alloc_pages_noprof+0x221/0x2470 mm/page_alloc.c:4751
alloc_pages_mpol_noprof+0x2c9/0x610 mm/mempolicy.c:2265
alloc_slab_page mm/slub.c:2408 [inline]
allocate_slab mm/slub.c:2574 [inline]
new_slab+0x2c9/0x410 mm/slub.c:2627
___slab_alloc+0xda4/0x1880 mm/slub.c:3815
__slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3905
__slab_alloc_node mm/slub.c:3980 [inline]
slab_alloc_node mm/slub.c:4141 [inline]
kmem_cache_alloc_noprof+0xfa/0x3d0 mm/slub.c:4160
p9_tag_alloc+0x9c/0x870 net/9p/client.c:281
p9_client_prepare_req+0x19f/0x4d0 net/9p/client.c:644
p9_client_rpc+0x1c3/0xc10 net/9p/client.c:691
p9_client_version net/9p/client.c:930 [inline]
p9_client_create+0xc65/0x1200 net/9p/client.c:1036
v9fs_session_init+0x1f8/0x1a80 fs/9p/v9fs.c:410
v9fs_mount+0xc6/0xa30 fs/9p/vfs_super.c:122
legacy_get_tree+0x109/0x220 fs/fs_context.c:662
vfs_get_tree+0x8f/0x380 fs/super.c:1814
page last free pid 6750 tgid 6748 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1127 [inline]
free_unref_folios+0xa7b/0x14f0 mm/page_alloc.c:2704
folios_put_refs+0x587/0x7b0 mm/swap.c:962
free_pages_and_swap_cache+0x45f/0x510 mm/swap_state.c:335
__tlb_batch_free_encoded_pages+0xf9/0x290 mm/mmu_gather.c:136
tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
tlb_flush_mmu mm/mmu_gather.c:373 [inline]
tlb_finish_mmu+0x168/0x7b0 mm/mmu_gather.c:465
exit_mmap+0x3df/0xb20 mm/mmap.c:1680
__mmput+0x12a/0x4c0 kernel/fork.c:1353
mmput+0x62/0x70 kernel/fork.c:1375
exit_mm kernel/exit.c:570 [inline]
do_exit+0x9bf/0x2d70 kernel/exit.c:925
do_group_exit+0xd3/0x2a0 kernel/exit.c:1087
get_signal+0x24ed/0x26c0 kernel/signal.c:3017
arch_do_signal_or_restart+0x90/0x7e0 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x150/0x2a0 kernel/entry/common.c:218
do_syscall_64+0xda/0x250 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88807b19e900: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
ffff88807b19e980: fc fc fa fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807b19ea00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
^
ffff88807b19ea80: fc fc fc fc 00 00 00 00 00 00 00 00 00 00 00 00
ffff88807b19eb00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc
==================================================================

Tested on:

commit: aaec5a95 pipe_read: don't wake up the writer if the pi..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=15fafde4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=8d5a2956e94d7972
dashboard link: https://syzkaller.appspot.com/bug?extid=62262fdc0e01d99573fc
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch: https://syzkaller.appspot.com/x/patch.diff?x=110a3804580000

Next message: Jarkko Sakkinen: "Re: [PATCH 4/4] x86/sgx: Implement ENCLS[EUPDATESVN] and opportunistically call it during first EPC page alloc"
Previous message: Ingo Molnar: "Re: [PATCH 4/5] bugs/x86: Augment warnings output by concatenating 'cond_str' with the regular __FILE__ string in _BUG_FLAGS()"
In reply to: K Prateek Nayak: "Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter"
Next in thread: asmadeus: "Re: [syzbot] [netfs?] INFO: task hung in netfs_unbuffered_write_iter"
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