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BUG: KASAN: slab-use-after-free in vma_multi_allowed+0x172/0x1b0
Read of size 8 at addr ffff88800d070198 by task syz-executor.2/5523

CPU: 0 UID: 0 PID: 5523 Comm: syz-executor.2 Not tainted 6.17.0-rc1-next-20250815 #1 PREEMPT(voluntary) 
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0xca/0x120
 print_report+0xcb/0x610
 kasan_report+0xca/0x100
 vma_multi_allowed+0x172/0x1b0
 __do_sys_mremap+0xcb7/0x1410
 do_syscall_64+0xbf/0x360
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd9b3f5fb19
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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd9b14d5188 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
RAX: ffffffffffffffda RBX: 00007fd9b4072f60 RCX: 00007fd9b3f5fb19
RDX: 0000000000004000 RSI: 0000000000004000 RDI: 0000000020ffc000
RBP: 00007fd9b3fb9f6d R08: 0000000020ff4000 R09: 0000000000000000
R10: 0000000000000007 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fff4c86e9ef R14: 00007fd9b14d5300 R15: 0000000000022000
 </TASK>

Allocated by task 5523:
 kasan_save_stack+0x24/0x50
 kasan_save_track+0x14/0x30
 __kasan_slab_alloc+0x59/0x70
 kmem_cache_alloc_noprof+0x13c/0x3d0
 vm_area_dup+0x25/0x6f0
 __split_vma+0x179/0xde0
 vms_gather_munmap_vmas+0x178/0xc70
 __mmap_region+0x44e/0x2670
 mmap_region+0x314/0x3e0
 do_mmap+0xa36/0x11d0
 do_shmat+0xfac/0x1310
 __x64_sys_shmat+0xcf/0x160
 do_syscall_64+0xbf/0x360
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 14:
 kasan_save_stack+0x24/0x50
 kasan_save_track+0x14/0x30
 kasan_save_free_info+0x3a/0x60
 __kasan_slab_free+0x3f/0x50
 slab_free_after_rcu_debug+0xd6/0x290
 rcu_core+0x7c8/0x1800
 handle_softirqs+0x1b1/0x770
 run_ksoftirqd+0x2e/0x60
 smpboot_thread_fn+0x41d/0x9d0
 kthread+0x3c8/0x740
 ret_from_fork+0x34b/0x430
 ret_from_fork_asm+0x1a/0x30

Last potentially related work creation:
 kasan_save_stack+0x24/0x50
 kasan_record_aux_stack+0x89/0xa0
 kmem_cache_free+0x145/0x460
 vms_complete_munmap_vmas+0x549/0x9f0
 do_vmi_align_munmap+0x3db/0x550
 do_vmi_munmap+0x1eb/0x3c0
 do_munmap+0xbd/0x100
 mremap_to+0x242/0x450
 __do_sys_mremap+0xca2/0x1410
 do_syscall_64+0xbf/0x360
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88800d070140
 which belongs to the cache vm_area_struct of size 256
The buggy address is located 88 bytes inside of
 freed 256-byte region [ffff88800d070140, ffff88800d070240)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xd070
memcg:ffff88801677da81
flags: 0x100000000000000(node=0|zone=1)
page_type: f5(slab)
raw: 0100000000000000 ffff888008fffc80 ffffea0000336fc0 dead000000000002
raw: 0000000000000000 00000000800c000c 00000000f5000000 ffff88801677da81
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88800d070080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88800d070100: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
>ffff88800d070180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff88800d070200: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff88800d070280: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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