KASAN: slab-use-after-free Read in str_to_user

Status: closed as invalid on 2026/05/19 14:07
Subsystems: input
Labels: prio:normal
[Documentation on labels]
First crash: 167d, last: 123d
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ID Workflow Result Correct Bug Created Started Finished Revision
72f25e53 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in str_to_user 2026/05/13 01:02 2026/05/13 01:02 2026/05/13 01:40 ac1aeadb
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 KASAN: slab-use-after-free Read in str_to_user 19 1 18d 18d 0/2 upstream: reported on 2026/08/05 01:22
upstream KASAN: slab-use-after-free Read in str_to_user (2) prio:high actionable input 19 2 18d 48d 0/29 upstream: reported on 2026/07/06 01:19

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in strlen+0x85/0xa0 lib/string.c:420
Read of size 1 at addr ffff88811b0c2a20 by task syz.4.3947/21992

CPU: 1 UID: 0 PID: 21992 Comm: syz.4.3947 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 strlen+0x85/0xa0 lib/string.c:420
 __fortify_strlen include/linux/fortify-string.h:266 [inline]
 str_to_user+0x26/0xa0 drivers/input/evdev.c:769
 evdev_do_ioctl+0x1529/0x1b60 drivers/input/evdev.c:1172
 evdev_ioctl_handler drivers/input/evdev.c:1270 [inline]
 evdev_ioctl+0x16f/0x1a0 drivers/input/evdev.c:1279
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0x7f0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbe21bec819
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:00007fbe20647028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fbe21e65fa0 RCX: 00007fbe21bec819
RDX: 00002000000011c0 RSI: 0000000080404507 RDI: 0000000000000003
RBP: 00007fbe21c82c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbe21e66038 R14: 00007fbe21e65fa0 R15: 00007fff15d42058
 </TASK>

Allocated by task 2863:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5295 [inline]
 __kvmalloc_node_noprof+0x323/0x950 mm/slub.c:6828
 bucket_table_alloc.isra.0+0x88/0x460 lib/rhashtable.c:186
 rhashtable_init_noprof+0x43b/0x7d0 lib/rhashtable.c:1076
 simple_xattrs_init fs/xattr.c:1618 [inline]
 simple_xattrs_alloc+0x5c/0xd0 fs/xattr.c:1641
 class_simple_xattrs_constructor include/linux/xattr.h:165 [inline]
 shmem_initxattrs+0x7d/0x6c0 mm/shmem.c:4237
 security_inode_init_security+0x23f/0x360 security/security.c:1370
 shmem_mknod+0x17b/0x2e0 mm/shmem.c:3868
 lookup_open.isra.0+0xc47/0x11b0 fs/namei.c:4511
 open_last_lookups fs/namei.c:4611 [inline]
 path_openat+0x2291/0x31a0 fs/namei.c:4855
 do_file_open+0x20e/0x430 fs/namei.c:4887
 do_sys_openat2+0x10d/0x1e0 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0x12d/0x210 fs/open.c:1381
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0x7f0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 2863:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x43/0x70 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2689 [inline]
 slab_free mm/slub.c:6246 [inline]
 kfree+0x204/0x650 mm/slub.c:6561
 rhashtable_free_and_destroy+0x16c/0x9b0 lib/rhashtable.c:1174
 shmem_evict_inode+0x1ae/0xc30 mm/shmem.c:1429
 evict+0x3c2/0xad0 fs/inode.c:841
 iput_final fs/inode.c:1960 [inline]
 iput fs/inode.c:2009 [inline]
 iput+0x79d/0xce0 fs/inode.c:1972
 filename_unlinkat+0x3b8/0x700 fs/namei.c:5572
 __do_sys_unlink fs/namei.c:5603 [inline]
 __se_sys_unlink fs/namei.c:5600 [inline]
 __x64_sys_unlink+0x46/0x70 fs/namei.c:5600
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0x7f0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88811b0c2800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 544 bytes inside of
 freed 1024-byte region [ffff88811b0c2800, ffff88811b0c2c00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88811b0c0000 pfn:0x11b0c0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x200000000000240(workingset|head|node=0|zone=2)
page_type: f5(slab)
raw: 0200000000000240 ffff888100041dc0 ffffea00046d8210 ffffea00044baa10
raw: ffff88811b0c0000 000000080010000f 00000000f5000000 0000000000000000
head: 0200000000000240 ffff888100041dc0 ffffea00046d8210 ffffea00044baa10
head: ffff88811b0c0000 000000080010000f 00000000f5000000 0000000000000000
head: 0200000000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 3900, tgid 3900 (kworker/u8:10), ts 73561085395, free_ts 73271380536
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x153/0x170 mm/page_alloc.c:1858
 prep_new_page mm/page_alloc.c:1866 [inline]
 get_page_from_freelist+0xf34/0x3a90 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x273/0x28a0 mm/page_alloc.c:5226
 alloc_slab_page mm/slub.c:3278 [inline]
 allocate_slab mm/slub.c:3467 [inline]
 new_slab+0xa6/0x6b0 mm/slub.c:3525
 refill_objects+0x277/0x420 mm/slub.c:7251
 refill_sheaf mm/slub.c:2816 [inline]
 __pcs_replace_empty_main+0x375/0x650 mm/slub.c:4651
 alloc_from_pcs mm/slub.c:4749 [inline]
 slab_alloc_node mm/slub.c:4883 [inline]
 __do_kmalloc_node mm/slub.c:5294 [inline]
 __kmalloc_noprof+0x645/0x810 mm/slub.c:5307
 kmalloc_noprof include/linux/slab.h:954 [inline]
 load_elf_phdrs+0x102/0x210 fs/binfmt_elf.c:540
 load_elf_binary+0x1561/0x50d0 fs/binfmt_elf.c:969
 search_binary_handler fs/exec.c:1664 [inline]
 exec_binprm fs/exec.c:1696 [inline]
 bprm_execve fs/exec.c:1748 [inline]
 bprm_execve+0x8ef/0x15e0 fs/exec.c:1724
 kernel_execve+0x31e/0x3a0 fs/exec.c:1892
 call_usermodehelper_exec_async+0x239/0x4b0 kernel/umh.c:109
 ret_from_fork+0x69a/0xc80 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page last free pid 3883 tgid 3883 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1402 [inline]
 __free_frozen_pages+0x692/0xf10 mm/page_alloc.c:2943
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x47/0xf0 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x4e/0x70 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4569 [inline]
 slab_alloc_node mm/slub.c:4898 [inline]
 kmem_cache_alloc_noprof+0x2e7/0x6a0 mm/slub.c:4905
 vm_area_dup+0x25/0x6e0 mm/vma_init.c:123
 __split_vma+0x18c/0xd60 mm/vma.c:516
 split_vma mm/vma.c:599 [inline]
 vma_modify+0x11ab/0x2290 mm/vma.c:1699
 vma_modify_flags+0x1f2/0x360 mm/vma.c:1719
 mprotect_fixup+0x27a/0xe30 mm/mprotect.c:789
 do_mprotect_pkey+0xa4b/0xef0 mm/mprotect.c:967
 __do_sys_mprotect mm/mprotect.c:988 [inline]
 __se_sys_mprotect mm/mprotect.c:985 [inline]
 __x64_sys_mprotect+0x78/0xc0 mm/mprotect.c:985
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0x7f0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88811b0c2900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88811b0c2980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88811b0c2a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88811b0c2a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88811b0c2b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/21 19:37 https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing c1f49dea2b8f 0b6ab7ec .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-usb KASAN: slab-use-after-free Read in str_to_user
2026/03/25 11:29 https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing 84db3719d273 8ee77f7d .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-usb KASAN: slab-use-after-free Read in str_to_user
2026/03/09 03:25 https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing bb375c251ab4 5cb44a80 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-usb KASAN: slab-use-after-free Read in str_to_user
* Struck through repros no longer work on HEAD.