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BUG: KASAN: slab-out-of-bounds in afs_split_string fs/afs/addr_prefs.c:51 [inline]
BUG: KASAN: slab-out-of-bounds in afs_proc_addr_prefs_write+0x13a9/0x15f0 fs/afs/addr_prefs.c:415
Read of size 1 at addr ffff88801b861ec7 by task syz.2.3491/27234

CPU: 1 UID: 0 PID: 27234 Comm: syz.2.3491 Not tainted 6.16.0-rc2-syzkaller-00082-gfb4d33ab452e #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
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:408 [inline]
 print_report+0xcd/0x680 mm/kasan/report.c:521
 kasan_report+0xe0/0x110 mm/kasan/report.c:634
 afs_split_string fs/afs/addr_prefs.c:51 [inline]
 afs_proc_addr_prefs_write+0x13a9/0x15f0 fs/afs/addr_prefs.c:415
 proc_simple_write+0x114/0x1b0 fs/proc/generic.c:825
 pde_write fs/proc/inode.c:330 [inline]
 proc_reg_write+0x240/0x330 fs/proc/inode.c:342
 do_loop_readv_writev fs/read_write.c:850 [inline]
 do_loop_readv_writev fs/read_write.c:835 [inline]
 vfs_writev+0x5dc/0xde0 fs/read_write.c:1059
 do_writev+0x132/0x340 fs/read_write.c:1103
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f686bb8e929
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:00007f686cadd038 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f686bdb5fa0 RCX: 00007f686bb8e929
RDX: 0000000000000003 RSI: 0000200000000080 RDI: 000000000000000b
RBP: 00007f686bc10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f686bdb5fa0 R15: 00007ffe97d93138
 </TASK>

Allocated by task 27234:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4328 [inline]
 __kmalloc_node_track_caller_noprof+0x221/0x510 mm/slub.c:4347
 memdup_user_nul+0x2b/0x120 mm/util.c:302
 proc_simple_write+0xc7/0x1b0 fs/proc/generic.c:822
 pde_write fs/proc/inode.c:330 [inline]
 proc_reg_write+0x240/0x330 fs/proc/inode.c:342
 do_loop_readv_writev fs/read_write.c:850 [inline]
 do_loop_readv_writev fs/read_write.c:835 [inline]
 vfs_writev+0x5dc/0xde0 fs/read_write.c:1059
 do_writev+0x132/0x340 fs/read_write.c:1103
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x490 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88801b861ec0
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes to the right of
 allocated 7-byte region [ffff88801b861ec0, ffff88801b861ec7)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1b861
anon flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88801b841500 0000000000000000 dead000000000001
raw: 0000000000000000 0000000080800080 00000000f5000000 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 0x0(), pid 0, tgid 0 (swapper), ts 1525669728, free_ts 0
 create_dummy_stack mm/page_owner.c:94 [inline]
 register_early_stack+0x89/0xd0 mm/page_owner.c:110
 init_page_owner+0x52/0x7e0 mm/page_owner.c:120
 invoke_init_callbacks mm/page_ext.c:148 [inline]
 page_ext_init+0x703/0xb00 mm/page_ext.c:497
 mm_core_init+0x13c/0x220 mm/mm_init.c:2783
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88801b861d80: fa fc fc fc 05 fc fc fc 05 fc fc fc 05 fc fc fc
 ffff88801b861e00: fa fc fc fc 05 fc fc fc 05 fc fc fc fa fc fc fc
>ffff88801b861e80: 05 fc fc fc 05 fc fc fc 07 fc fc fc 05 fc fc fc
                                           ^
 ffff88801b861f00: fa fc fc fc fa fc fc fc fa fc fc fc 00 fc fc fc
 ffff88801b861f80: 00 fc fc fc 00 fc fc fc fa fc fc fc 05 fc fc fc
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