Kernel bug: KASAN: slab-use-after-free Write in iommufd_eventq_fops_release
Subsystem: iommu
Status: fixed

Crash report:
R13: 00007fb44b1d5fa0 R14: 00007fb44b1d5fa0 R15: 0000000000000003
 </TASK>
==================================================================
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_dec include/linux/refcount.h:455 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec include/linux/refcount.h:476 [inline]
BUG: KASAN: slab-use-after-free in iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376
Write of size 4 at addr ffff888059c97804 by task syz.0.46/6164

CPU: 0 UID: 0 PID: 6164 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 check_region_inline mm/kasan/generic.c:183 [inline]
 kasan_check_range+0x100/0x1b0 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_dec include/linux/refcount.h:455 [inline]
 refcount_dec include/linux/refcount.h:476 [inline]
 iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376
 __fput+0x402/0xb70 fs/file_table.c:468
 task_work_run+0x14d/0x240 kernel/task_work.c:227
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x41c/0x4c0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb44af8eba9
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:00007ffc3d692818 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: fffffffffffffff2 RBX: 00007fb44b1d5fa0 RCX: 00007fb44af8eba9
RDX: 0000000000000004 RSI: 0000000000003b8e RDI: 0000000000000006
RBP: 00007ffc3d692870 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fb44b1d5fa0 R14: 00007fb44b1d5fa0 R15: 0000000000000003
 </TASK>

Allocated by task 6164:
 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:388 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:405
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4376 [inline]
 __kmalloc_noprof+0x223/0x510 mm/slub.c:4388
 kmalloc_noprof include/linux/slab.h:909 [inline]
 kzalloc_noprof include/linux/slab.h:1039 [inline]
 _iommufd_object_alloc+0x23/0x1a0 drivers/iommu/iommufd/main.c:40
 _iommufd_object_alloc_ucmd+0xb2/0x160 drivers/iommu/iommufd/main.c:84
 iommufd_fault_alloc+0x93/0x420 drivers/iommu/iommufd/eventq.c:430
 iommufd_fops_ioctl+0x34d/0x540 drivers/iommu/iommufd/main.c:508
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl fs/ioctl.c:584 [inline]
 __x64_sys_ioctl+0x18b/0x210 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6164:
 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:243 [inline]
 __kasan_slab_free+0x60/0x70 mm/kasan/common.c:275
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2422 [inline]
 slab_free mm/slub.c:4695 [inline]
 kfree+0x2b4/0x4d0 mm/slub.c:4894
 iommufd_object_abort+0x10c/0x170 drivers/iommu/iommufd/main.c:124
 iommufd_fops_ioctl+0x381/0x540 drivers/iommu/iommufd/main.c:512
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl fs/ioctl.c:584 [inline]
 __x64_sys_ioctl+0x18b/0x210 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888059c97800
 which belongs to the cache kmalloc-cg-512 of size 512
The buggy address is located 4 bytes inside of
 freed 512-byte region [ffff888059c97800, ffff888059c97a00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x59c94
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888026413e01
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b84b140 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000100010 00000000f5000000 ffff888026413e01
head: 00fff00000000040 ffff88801b84b140 dead000000000122 0000000000000000
head: 0000000000000000 0000000000100010 00000000f5000000 ffff888026413e01
head: 00fff00000000002 ffffea0001672501 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
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 5224, tgid 5224 (klogd), ts 132635729272, free_ts 132529818110
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1851
 prep_new_page mm/page_alloc.c:1859 [inline]
 get_page_from_freelist+0x132b/0x38e0 mm/page_alloc.c:3858
 __alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:5148
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
 alloc_slab_page mm/slub.c:2492 [inline]
 allocate_slab mm/slub.c:2660 [inline]
 new_slab+0x247/0x330 mm/slub.c:2714
 ___slab_alloc+0xcf2/0x1750 mm/slub.c:3901
 __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3992
 __slab_alloc_node mm/slub.c:4067 [inline]
 slab_alloc_node mm/slub.c:4228 [inline]
 __do_kmalloc_node mm/slub.c:4375 [inline]
 __kmalloc_node_track_caller_noprof+0x2ee/0x510 mm/slub.c:4395
 kmalloc_reserve+0xef/0x2c0 net/core/skbuff.c:600
 __alloc_skb+0x166/0x380 net/core/skbuff.c:669
 alloc_skb include/linux/skbuff.h:1336 [inline]
 alloc_skb_with_frags+0xe0/0x860 net/core/skbuff.c:6665
 sock_alloc_send_pskb+0x7fb/0x990 net/core/sock.c:2958
 unix_dgram_sendmsg+0x3e9/0x17f0 net/unix/af_unix.c:2153
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 __sys_sendto+0x4a3/0x520 net/socket.c:2228
 __do_sys_sendto net/socket.c:2235 [inline]
 __se_sys_sendto net/socket.c:2231 [inline]
 __x64_sys_sendto+0xe0/0x1c0 net/socket.c:2231
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
page last free pid 5980 tgid 5980 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0x7d5/0x10f0 mm/page_alloc.c:2895
 discard_slab mm/slub.c:2758 [inline]
 __put_partials+0x165/0x1c0 mm/slub.c:3223
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x4d/0x120 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:340
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4191 [inline]
 slab_alloc_node mm/slub.c:4240 [inline]
 kmem_cache_alloc_noprof+0x1cb/0x3b0 mm/slub.c:4247
 getname_flags.part.0+0x4c/0x550 fs/namei.c:146
 getname_flags include/linux/audit.h:322 [inline]
 getname include/linux/fs.h:2919 [inline]
 __do_sys_unlink fs/namei.c:4696 [inline]
 __se_sys_unlink fs/namei.c:4694 [inline]
 __x64_sys_unlink+0xb0/0x110 fs/namei.c:4694
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888059c97700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888059c97780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888059c97800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888059c97880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888059c97900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================