[v6.6] KASAN: slab-use-after-free Write in nfsd_create_serv
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syzbot
Jul 27, 2026, 7:02:40 PMJul 27
to syzkaller...@googlegroups.com
Hello,
syzbot found the following issue on:
HEAD commit: c5596480c50e Linux 6.6.145
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13d69632580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=d5a0bec1fa88dd2ce67b
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eb5cda0a8020/disk-c5596480.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ca05ff2fc502/vmlinux-c5596480.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6daf3255b985/bzImage-c5596480.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d5a0be...@syzkaller.appspotmail.com
==================================================================
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_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: slab-use-after-free in __refcount_add include/linux/refcount.h:193 [inline]
BUG: KASAN: slab-use-after-free in __refcount_inc include/linux/refcount.h:250 [inline]
BUG: KASAN: slab-use-after-free in refcount_inc include/linux/refcount.h:267 [inline]
BUG: KASAN: slab-use-after-free in kref_get include/linux/kref.h:45 [inline]
BUG: KASAN: slab-use-after-free in svc_get include/linux/sunrpc/svc.h:109 [inline]
BUG: KASAN: slab-use-after-free in nfsd_create_serv+0x116/0x5c0 fs/nfsd/nfssvc.c:666
Write of size 4 at addr ffff88801c39d850 by task syz.1.24/5917
CPU: 1 PID: 5917 Comm: syz.1.24 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:468
kasan_report+0x117/0x150 mm/kasan/report.c:581
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x241/0x290 mm/kasan/generic.c:187
instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
__refcount_add include/linux/refcount.h:193 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
kref_get include/linux/kref.h:45 [inline]
svc_get include/linux/sunrpc/svc.h:109 [inline]
nfsd_create_serv+0x116/0x5c0 fs/nfsd/nfssvc.c:666
nfsd_svc+0x183/0xab0 fs/nfsd/nfssvc.c:801
write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f9e4ef9de99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9e4fe50028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9e4f226180 RCX: 00007f9e4ef9de99
RDX: 0000000000000002 RSI: 0000200000000240 RDI: 0000000000000004
RBP: 00007f9e4f033eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9e4f226218 R14: 00007f9e4f226180 R15: 00007ffd7ac37928
</TASK>
Allocated by task 5915:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
____kasan_kmalloc mm/kasan/common.c:375 [inline]
__kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
__svc_create+0x60/0xa20 net/sunrpc/svc.c:464
svc_create_pooled+0x66a/0x7e0 net/sunrpc/svc.c:556
nfsd_create_serv+0x29f/0x5c0 fs/nfsd/nfssvc.c:672
__write_ports_addfd fs/nfsd/nfsctl.c:712 [inline]
__write_ports fs/nfsd/nfsctl.c:788 [inline]
write_ports+0x698/0xfa0 fs/nfsd/nfsctl.c:844
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
Freed by task 5915:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x28/0x40 mm/kasan/generic.c:522
____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1811 [inline]
slab_free_freelist_hook+0x130/0x1a0 mm/slub.c:1837
slab_free mm/slub.c:3830 [inline]
__kmem_cache_free+0xba/0x1f0 mm/slub.c:3843
kref_put include/linux/kref.h:65 [inline]
svc_put include/linux/sunrpc/svc.h:124 [inline]
__write_ports_addfd fs/nfsd/nfsctl.c:724 [inline]
__write_ports fs/nfsd/nfsctl.c:788 [inline]
write_ports+0xb1a/0xfa0 fs/nfsd/nfsctl.c:844
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
The buggy address belongs to the object at ffff88801c39d800
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 80 bytes inside of
freed 512-byte region [ffff88801c39d800, ffff88801c39da00)
The buggy address belongs to the physical page:
page:ffffea000070e700 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1c39c
head:ffffea000070e700 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017c41c80 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 7985870575, free_ts 0
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
prep_new_page mm/page_alloc.c:1589 [inline]
get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
__alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
alloc_page_interleave+0x24/0x1e0 mm/mempolicy.c:2118
alloc_slab_page+0x5d/0x180 mm/slub.c:1881
allocate_slab mm/slub.c:2028 [inline]
new_slab+0x87/0x2d0 mm/slub.c:2081
___slab_alloc+0xc5c/0x12f0 mm/slub.c:3253
__slab_alloc mm/slub.c:3339 [inline]
__slab_alloc_node mm/slub.c:3392 [inline]
slab_alloc_node mm/slub.c:3485 [inline]
__kmem_cache_alloc_node+0x11f/0x250 mm/slub.c:3534
kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
device_private_init drivers/base/core.c:3530 [inline]
device_add+0xb6/0xc40 drivers/base/core.c:3581
tty_register_device_attr+0x425/0x950 drivers/tty/tty_io.c:3251
tty_register_device drivers/tty/tty_io.c:3186 [inline]
tty_register_driver+0x598/0xb30 drivers/tty/tty_io.c:3449
legacy_pty_init+0x3a6/0x600 drivers/tty/pty.c:579
pty_init+0xe/0x20 drivers/tty/pty.c:943
do_one_initcall+0x242/0x790 init/main.c:1249
do_initcall_level+0x13d/0x1f0 init/main.c:1311
page_owner free stack trace missing
Memory state around the buggy address:
ffff88801c39d700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801c39d780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801c39d800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88801c39d880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88801c39d900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
---
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 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
syzbot found the following issue on:
HEAD commit: c5596480c50e Linux 6.6.145
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=13d69632580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=d5a0bec1fa88dd2ce67b
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/eb5cda0a8020/disk-c5596480.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ca05ff2fc502/vmlinux-c5596480.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6daf3255b985/bzImage-c5596480.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d5a0be...@syzkaller.appspotmail.com
==================================================================
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_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: slab-use-after-free in __refcount_add include/linux/refcount.h:193 [inline]
BUG: KASAN: slab-use-after-free in __refcount_inc include/linux/refcount.h:250 [inline]
BUG: KASAN: slab-use-after-free in refcount_inc include/linux/refcount.h:267 [inline]
BUG: KASAN: slab-use-after-free in kref_get include/linux/kref.h:45 [inline]
BUG: KASAN: slab-use-after-free in svc_get include/linux/sunrpc/svc.h:109 [inline]
BUG: KASAN: slab-use-after-free in nfsd_create_serv+0x116/0x5c0 fs/nfsd/nfssvc.c:666
Write of size 4 at addr ffff88801c39d850 by task syz.1.24/5917
CPU: 1 PID: 5917 Comm: syz.1.24 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:468
kasan_report+0x117/0x150 mm/kasan/report.c:581
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x241/0x290 mm/kasan/generic.c:187
instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
__refcount_add include/linux/refcount.h:193 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
kref_get include/linux/kref.h:45 [inline]
svc_get include/linux/sunrpc/svc.h:109 [inline]
nfsd_create_serv+0x116/0x5c0 fs/nfsd/nfssvc.c:666
nfsd_svc+0x183/0xab0 fs/nfsd/nfssvc.c:801
write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f9e4ef9de99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9e4fe50028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9e4f226180 RCX: 00007f9e4ef9de99
RDX: 0000000000000002 RSI: 0000200000000240 RDI: 0000000000000004
RBP: 00007f9e4f033eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9e4f226218 R14: 00007f9e4f226180 R15: 00007ffd7ac37928
</TASK>
Allocated by task 5915:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
____kasan_kmalloc mm/kasan/common.c:375 [inline]
__kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
__svc_create+0x60/0xa20 net/sunrpc/svc.c:464
svc_create_pooled+0x66a/0x7e0 net/sunrpc/svc.c:556
nfsd_create_serv+0x29f/0x5c0 fs/nfsd/nfssvc.c:672
__write_ports_addfd fs/nfsd/nfsctl.c:712 [inline]
__write_ports fs/nfsd/nfsctl.c:788 [inline]
write_ports+0x698/0xfa0 fs/nfsd/nfsctl.c:844
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
Freed by task 5915:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x28/0x40 mm/kasan/generic.c:522
____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1811 [inline]
slab_free_freelist_hook+0x130/0x1a0 mm/slub.c:1837
slab_free mm/slub.c:3830 [inline]
__kmem_cache_free+0xba/0x1f0 mm/slub.c:3843
kref_put include/linux/kref.h:65 [inline]
svc_put include/linux/sunrpc/svc.h:124 [inline]
__write_ports_addfd fs/nfsd/nfsctl.c:724 [inline]
__write_ports fs/nfsd/nfsctl.c:788 [inline]
write_ports+0xb1a/0xfa0 fs/nfsd/nfsctl.c:844
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
The buggy address belongs to the object at ffff88801c39d800
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 80 bytes inside of
freed 512-byte region [ffff88801c39d800, ffff88801c39da00)
The buggy address belongs to the physical page:
page:ffffea000070e700 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1c39c
head:ffffea000070e700 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017c41c80 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 7985870575, free_ts 0
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
prep_new_page mm/page_alloc.c:1589 [inline]
get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
__alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
alloc_page_interleave+0x24/0x1e0 mm/mempolicy.c:2118
alloc_slab_page+0x5d/0x180 mm/slub.c:1881
allocate_slab mm/slub.c:2028 [inline]
new_slab+0x87/0x2d0 mm/slub.c:2081
___slab_alloc+0xc5c/0x12f0 mm/slub.c:3253
__slab_alloc mm/slub.c:3339 [inline]
__slab_alloc_node mm/slub.c:3392 [inline]
slab_alloc_node mm/slub.c:3485 [inline]
__kmem_cache_alloc_node+0x11f/0x250 mm/slub.c:3534
kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
device_private_init drivers/base/core.c:3530 [inline]
device_add+0xb6/0xc40 drivers/base/core.c:3581
tty_register_device_attr+0x425/0x950 drivers/tty/tty_io.c:3251
tty_register_device drivers/tty/tty_io.c:3186 [inline]
tty_register_driver+0x598/0xb30 drivers/tty/tty_io.c:3449
legacy_pty_init+0x3a6/0x600 drivers/tty/pty.c:579
pty_init+0xe/0x20 drivers/tty/pty.c:943
do_one_initcall+0x242/0x790 init/main.c:1249
do_initcall_level+0x13d/0x1f0 init/main.c:1311
page_owner free stack trace missing
Memory state around the buggy address:
ffff88801c39d700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88801c39d780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801c39d800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88801c39d880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88801c39d900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
---
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 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
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