================================================================== BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:102 [inline] BUG: KASAN: use-after-free in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline] BUG: KASAN: use-after-free in __refcount_add include/linux/refcount.h:193 [inline] BUG: KASAN: use-after-free in __refcount_inc include/linux/refcount.h:250 [inline] BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:267 [inline] BUG: KASAN: use-after-free in kref_get include/linux/kref.h:45 [inline] BUG: KASAN: use-after-free in svc_get include/linux/sunrpc/svc.h:108 [inline] BUG: KASAN: use-after-free in nfsd_create_serv+0x104/0x6a4 fs/nfsd/nfssvc.c:661 Write of size 4 at addr ffff0000f31bd450 by task syz.4.146/6464 CPU: 0 PID: 6464 Comm: syz.4.146 Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026 Call trace: dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:158 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165 __dump_stack+0x30/0x40 lib/dump_stack.c:88 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106 print_address_description+0x88/0x218 mm/kasan/report.c:316 print_report+0x50/0x68 mm/kasan/report.c:420 kasan_report+0xa8/0xfc mm/kasan/report.c:524 check_region_inline mm/kasan/generic.c:-1 [inline] kasan_check_range+0x258/0x290 mm/kasan/generic.c:189 __kasan_check_write+0x2c/0x3c mm/kasan/shadow.c:37 instrument_atomic_read_write include/linux/instrumented.h:102 [inline] atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [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:108 [inline] nfsd_create_serv+0x104/0x6a4 fs/nfsd/nfssvc.c:661 nfsd_svc+0x168/0x948 fs/nfsd/nfssvc.c:796 write_threads+0x2b4/0x310 fs/nfsd/nfsctl.c:424 nfsctl_transaction_write+0x114/0x164 fs/nfsd/nfsctl.c:114 vfs_write+0x2a8/0x7c8 fs/read_write.c:582 ksys_write+0x12c/0x228 fs/read_write.c:637 __do_sys_write fs/read_write.c:649 [inline] __se_sys_write fs/read_write.c:646 [inline] __arm64_sys_write+0x7c/0x90 fs/read_write.c:646 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585 Allocated by task 6464: kasan_save_stack mm/kasan/common.c:46 [inline] kasan_set_track+0x4c/0x80 mm/kasan/common.c:53 kasan_save_alloc_info+0x24/0x30 mm/kasan/generic.c:505 ____kasan_kmalloc mm/kasan/common.c:375 [inline] __kasan_kmalloc+0xa0/0xb8 mm/kasan/common.c:384 kasan_kmalloc include/linux/kasan.h:211 [inline] kmalloc_trace+0x7c/0x94 mm/slab_common.c:1031 kmalloc include/linux/slab.h:563 [inline] kzalloc include/linux/slab.h:699 [inline] __svc_create+0x80/0x89c net/sunrpc/svc.c:491 svc_create_pooled+0x648/0x7d8 net/sunrpc/svc.c:579 nfsd_create_serv+0x284/0x6a4 fs/nfsd/nfssvc.c:667 __write_ports_addxprt fs/nfsd/nfsctl.c:750 [inline] __write_ports fs/nfsd/nfsctl.c:794 [inline] write_ports+0x3e0/0x9f0 fs/nfsd/nfsctl.c:847 nfsctl_transaction_write+0x114/0x164 fs/nfsd/nfsctl.c:114 vfs_write+0x2a8/0x7c8 fs/read_write.c:582 ksys_write+0x12c/0x228 fs/read_write.c:637 __do_sys_write fs/read_write.c:649 [inline] __se_sys_write fs/read_write.c:646 [inline] __arm64_sys_write+0x7c/0x90 fs/read_write.c:646 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585 Freed by task 6464: kasan_save_stack mm/kasan/common.c:46 [inline] kasan_set_track+0x4c/0x80 mm/kasan/common.c:53 kasan_save_free_info+0x38/0x5c mm/kasan/generic.c:516 ____kasan_slab_free+0x148/0x1b0 mm/kasan/common.c:237 __kasan_slab_free+0x18/0x28 mm/kasan/common.c:245 kasan_slab_free include/linux/kasan.h:177 [inline] slab_free_hook mm/slub.c:1729 [inline] slab_free_freelist_hook+0x16c/0x1e8 mm/slub.c:1755 slab_free mm/slub.c:3687 [inline] __kmem_cache_free+0xbc/0x21c mm/slub.c:3700 kfree+0xd0/0x1a8 mm/slab_common.c:988 svc_destroy+0x144/0x184 net/sunrpc/svc.c:613 kref_put include/linux/kref.h:65 [inline] svc_put include/linux/sunrpc/svc.h:123 [inline] __write_ports_addxprt fs/nfsd/nfsctl.c:780 [inline] __write_ports fs/nfsd/nfsctl.c:794 [inline] write_ports+0x6ec/0x9f0 fs/nfsd/nfsctl.c:847 nfsctl_transaction_write+0x114/0x164 fs/nfsd/nfsctl.c:114 vfs_write+0x2a8/0x7c8 fs/read_write.c:582 ksys_write+0x12c/0x228 fs/read_write.c:637 __do_sys_write fs/read_write.c:649 [inline] __se_sys_write fs/read_write.c:646 [inline] __arm64_sys_write+0x7c/0x90 fs/read_write.c:646 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585 The buggy address belongs to the object at ffff0000f31bd400 which belongs to the cache kmalloc-512 of size 512 The buggy address is located 80 bytes inside of 512-byte region [ffff0000f31bd400, ffff0000f31bd600) The buggy address belongs to the physical page: page:000000005abdb4ec refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1331bc head:000000005abdb4ec order:2 compound_mapcount:0 compound_pincount:0 flags: 0x5ffc00000010200(slab|head|node=0|zone=2|lastcpupid=0x7ff) raw: 05ffc00000010200 0000000000000000 dead000000000001 ffff0000c0002600 raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff0000f31bd300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff0000f31bd380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >ffff0000f31bd400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff0000f31bd480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ffff0000f31bd500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ================================================================== ------------[ cut here ]------------ refcount_t: addition on 0; use-after-free. WARNING: CPU: 0 PID: 6464 at lib/refcount.c:25 refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25 Modules linked in: CPU: 0 PID: 6464 Comm: syz.4.146 Tainted: G B syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026 pstate: 62400005 (nZCv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=--) pc : refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25 lr : refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25 sp : ffff800020f47780 x29: ffff800020f47780 x28: dfff800000000000 x27: 1fffe0001b4f6058 x26: ffff0000da7b02c0 x25: ffff800020f477c0 x24: dfff800000000000 x23: ffff7000041e8ef8 x22: ffff80001c772000 x21: ffff0000d6421c40 x20: ffff0000f31bd450 x19: ffff800017d98000 x18: 1fffe00033e6997e x17: ffff8000153bd000 x16: ffff800008043b30 x15: 0000000040000000 x14: 0000000000000001 x13: 1fffe00033e6c070 x12: 0000000000000000 x11: ff00800008048e14 x10: 0000000040000002 x9 : c107c6bfc1fb4100 x8 : c107c6bfc1fb4100 x7 : ffff800011d1c160 x6 : ffff80000825ab20 x5 : 0000000000000000 x4 : 0000000000000001 x3 : 0000000000000000 x2 : ffff800020f47340 x1 : 0000000000000000 x0 : ffff80000825abb4 Call trace: refcount_warn_saturate+0x134/0x1f8 lib/refcount.c:25 __refcount_add include/linux/refcount.h:-1 [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:108 [inline] nfsd_create_serv+0x510/0x6a4 fs/nfsd/nfssvc.c:661 nfsd_svc+0x168/0x948 fs/nfsd/nfssvc.c:796 write_threads+0x2b4/0x310 fs/nfsd/nfsctl.c:424 nfsctl_transaction_write+0x114/0x164 fs/nfsd/nfsctl.c:114 vfs_write+0x2a8/0x7c8 fs/read_write.c:582 ksys_write+0x12c/0x228 fs/read_write.c:637 __do_sys_write fs/read_write.c:649 [inline] __se_sys_write fs/read_write.c:646 [inline] __arm64_sys_write+0x7c/0x90 fs/read_write.c:646 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585 irq event stamp: 2395 hardirqs last enabled at (2395): [] raw_spin_rq_unlock_irq kernel/sched/sched.h:1374 [inline] hardirqs last enabled at (2395): [] finish_lock_switch+0xb0/0x1c8 kernel/sched/core.c:5005 hardirqs last disabled at (2394): [] __schedule+0x294/0x1a6c kernel/sched/core.c:6461 softirqs last enabled at (1754): [] local_bh_enable+0x10/0x34 include/linux/bottom_half.h:32 softirqs last disabled at (1752): [] local_bh_disable+0x10/0x34 include/linux/bottom_half.h:19 ---[ end trace 0000000000000000 ]--- Internal error: SP/PC alignment exception: 000000008a000000 [#1] PREEMPT SMP Modules linked in: CPU: 0 PID: 6464 Comm: syz.4.146 Tainted: G B W syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026 pstate: 02400805 (nzcv daif +PAN -UAO +TCO -DIT -SSBS BTYPE=-c) pc : 0xffffffffffffffff x26: 0000000000000000 x25: 0000000000000000 x24: 1fffe0001b316232 x23: ffff0000d98b1180 x22: ffff0000d6421c40 x21: 0000000000000011 x20: 0000000000000801 x19: 1fffe0001b316238 x18: 0000000000000060 x17: 0000000000001000 x16: ffff800008043b30 x15: 0000000000000000 x14: 00000000ffff8000 x13: 00000000778d7487 x12: 0000000000080000 x11: ff00800010f3079c x10: 0000000000000002 x9 : ffff80001c635b50 x8 : ffffffffffffffff x7 : 0000000000000000 x6 : 000000000000003f x5 : 0000000000000801 x4 : 0000000000000011 x3 : 0000000000000002 x2 : 0000000000000000 x1 : ffff0000d98b1180 x0 : ffff0000d6421c40 Call trace: 0xffffffffffffffff svc_setup_socket+0x118/0xe5c net/sunrpc/svcsock.c:1308 svc_create_socket+0x590/0x874 net/sunrpc/svcsock.c:1464 svc_udp_create+0x4c/0x64 net/sunrpc/svcsock.c:627 __svc_xpo_create net/sunrpc/svc_xprt.c:244 [inline] _svc_xprt_create+0x28c/0x76c net/sunrpc/svc_xprt.c:307 svc_xprt_create+0x5c/0xd8 net/sunrpc/svc_xprt.c:345 nfsd_init_socks fs/nfsd/nfssvc.c:295 [inline] nfsd_startup_net fs/nfsd/nfssvc.c:411 [inline] nfsd_svc+0x350/0x948 fs/nfsd/nfssvc.c:801 write_threads+0x2b4/0x310 fs/nfsd/nfsctl.c:424 nfsctl_transaction_write+0x114/0x164 fs/nfsd/nfsctl.c:114 vfs_write+0x2a8/0x7c8 fs/read_write.c:582 ksys_write+0x12c/0x228 fs/read_write.c:637 __do_sys_write fs/read_write.c:649 [inline] __se_sys_write fs/read_write.c:646 [inline] __arm64_sys_write+0x7c/0x90 fs/read_write.c:646 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] invoke_syscall+0x98/0x290 arch/arm64/kernel/syscall.c:52 el0_svc_common+0x13c/0x258 arch/arm64/kernel/syscall.c:140 do_el0_svc+0x5c/0x134 arch/arm64/kernel/syscall.c:204 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585 Code: bad PC value ---[ end trace 0000000000000000 ]---