Re: [syzbot] [netfs?] WARNING: refcount bug in netfs_put_subrequest

[syzbot <syzbot+d9890527385ab9767e03@syzkaller.appspotmail.com>]

Hello,

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

netfs: Couldn't get user pages (rc=-14)
==================================================================
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_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:264 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:307 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:325 [inline]
BUG: KASAN: slab-use-after-free in iocb_put fs/aio.c:1208 [inline]
BUG: KASAN: slab-use-after-free in io_submit_one+0x4e5/0x1da0 fs/aio.c:2055
Write of size 4 at addr ffff88802e13ae88 by task syz.1.40/6596

CPU: 3 UID: 0 PID: 6596 Comm: syz.1.40 Not tainted 6.14.0-rc2-syzkaller-g128c8f96eb86-dirty #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
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
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:264 [inline]
 __refcount_dec_and_test include/linux/refcount.h:307 [inline]
 refcount_dec_and_test include/linux/refcount.h:325 [inline]
 iocb_put fs/aio.c:1208 [inline]
 io_submit_one+0x4e5/0x1da0 fs/aio.c:2055
 __do_sys_io_submit fs/aio.c:2111 [inline]
 __se_sys_io_submit fs/aio.c:2081 [inline]
 __x64_sys_io_submit+0x1b2/0x340 fs/aio.c:2081
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8f53d8cde9
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:00007f8f54b7f038 EFLAGS: 00000246 ORIG_RAX: 00000000000000d1
RAX: ffffffffffffffda RBX: 00007f8f53fa5fa0 RCX: 00007f8f53d8cde9
RDX: 00004000000002c0 RSI: 0000000000000001 RDI: 00007f8f54b5e000
RBP: 00007f8f53e0e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f8f53fa5fa0 R15: 00007ffeeb0594c8
 </TASK>

Allocated by task 6596:
 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:4115 [inline]
 slab_alloc_node mm/slub.c:4164 [inline]
 kmem_cache_alloc_noprof+0x226/0x3d0 mm/slub.c:4171
 aio_get_req fs/aio.c:1058 [inline]
 io_submit_one+0x123/0x1da0 fs/aio.c:2048
 __do_sys_io_submit fs/aio.c:2111 [inline]
 __se_sys_io_submit fs/aio.c:2081 [inline]
 __x64_sys_io_submit+0x1b2/0x340 fs/aio.c:2081
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6596:
 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:576
 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:2353 [inline]
 slab_free mm/slub.c:4609 [inline]
 kmem_cache_free+0x2e2/0x4d0 mm/slub.c:4711
 iocb_destroy fs/aio.c:1110 [inline]
 iocb_put fs/aio.c:1210 [inline]
 iocb_put fs/aio.c:1206 [inline]
 aio_complete_rw+0x3ec/0x7b0 fs/aio.c:1507
 netfs_rreq_assess_dio fs/netfs/read_collect.c:379 [inline]
 netfs_read_collection+0x30fa/0x3cf0 fs/netfs/read_collect.c:442
 netfs_wait_for_pause+0x31c/0x3e0 fs/netfs/read_collect.c:693
 netfs_dispatch_unbuffered_reads fs/netfs/direct_read.c:106 [inline]
 netfs_unbuffered_read fs/netfs/direct_read.c:144 [inline]
 netfs_unbuffered_read_iter_locked+0xb50/0x1610 fs/netfs/direct_read.c:229
 netfs_unbuffered_read_iter+0xc5/0x100 fs/netfs/direct_read.c:264
 v9fs_file_read_iter+0xbf/0x100 fs/9p/vfs_file.c:361
 aio_read+0x313/0x4e0 fs/aio.c:1602
 __io_submit_one fs/aio.c:2003 [inline]
 io_submit_one+0x1580/0x1da0 fs/aio.c:2052
 __do_sys_io_submit fs/aio.c:2111 [inline]
 __se_sys_io_submit fs/aio.c:2081 [inline]
 __x64_sys_io_submit+0x1b2/0x340 fs/aio.c:2081
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88802e13adc0
 which belongs to the cache aio_kiocb of size 216
The buggy address is located 200 bytes inside of
 freed 216-byte region [ffff88802e13adc0, ffff88802e13ae98)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88802e13af00 pfn:0x2e13a
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 ffff888020025cc0 dead000000000122 0000000000000000
raw: ffff88802e13af00 0000000080190010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff888020025cc0 dead000000000122 0000000000000000
head: ffff88802e13af00 0000000080190010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffea0000b84e81 ffffffffffffffff 0000000000000000
head: 0000000000000002 0000000000000000 00000000ffffffff 0000000000000000
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 6485, tgid 6484 (syz.1.20), ts 73097474485, free_ts 73096375881
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x181/0x1b0 mm/page_alloc.c:1551
 prep_new_page mm/page_alloc.c:1559 [inline]
 get_page_from_freelist+0xfce/0x2f80 mm/page_alloc.c:3477
 __alloc_frozen_pages_noprof+0x221/0x2470 mm/page_alloc.c:4739
 alloc_pages_mpol+0x1fc/0x540 mm/mempolicy.c:2270
 alloc_slab_page mm/slub.c:2423 [inline]
 allocate_slab mm/slub.c:2587 [inline]
 new_slab+0x23d/0x330 mm/slub.c:2640
 ___slab_alloc+0xc5d/0x1720 mm/slub.c:3826
 __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3916
 __slab_alloc_node mm/slub.c:3991 [inline]
 slab_alloc_node mm/slub.c:4152 [inline]
 kmem_cache_alloc_noprof+0xfa/0x3d0 mm/slub.c:4171
 aio_get_req fs/aio.c:1058 [inline]
 io_submit_one+0x123/0x1da0 fs/aio.c:2048
 __do_sys_io_submit fs/aio.c:2111 [inline]
 __se_sys_io_submit fs/aio.c:2081 [inline]
 __x64_sys_io_submit+0x1b2/0x340 fs/aio.c:2081
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 34 tgid 34 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1127 [inline]
 free_frozen_pages+0x6db/0xfb0 mm/page_alloc.c:2660
 rcu_do_batch kernel/rcu/tree.c:2546 [inline]
 rcu_core+0x79d/0x14d0 kernel/rcu/tree.c:2802
 handle_softirqs+0x213/0x8f0 kernel/softirq.c:561
 run_ksoftirqd kernel/softirq.c:950 [inline]
 run_ksoftirqd+0x3a/0x60 kernel/softirq.c:942
 smpboot_thread_fn+0x661/0xa30 kernel/smpboot.c:164
 kthread+0x3af/0x750 kernel/kthread.c:464
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Memory state around the buggy address:
 ffff88802e13ad80: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
 ffff88802e13ae00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88802e13ae80: fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc fc
                      ^
 ffff88802e13af00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88802e13af80: fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc fc
==================================================================


Tested on:

commit:         128c8f96 Merge tag 'drm-fixes-2025-02-14' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17c659b0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c09dc55ba7f798e3
dashboard link: https://syzkaller.appspot.com/bug?extid=d9890527385ab9767e03
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=102087df980000