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

Status: upstream: reported C repro on 2023/07/23 09:04
Subsystems: mm
[Documentation on labels]
Reported-by: syzbot+173cc8cfdfbbef6dd755@syzkaller.appspotmail.com
Fix commit: mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock(): fix
Patched on: [ci-upstream-linux-next-kasan-gce-root], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci-upstream-rust-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 1102d, last: 1097d
Cause bisection: failed (error log, bisect log)
  
▶ ▼ ✨ AI Jobs (6)
ID Workflow Result Correct Bug Created Started Finished Revision Error
f58a92ff assessment-security 💥 KASAN: slab-use-after-free Read in madvise_collapse 2026/07/05 05:06 2026/07/05 05:06 2026/07/05 05:27 93f57954 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/3d5252f3447edc39d3...
truncated to first 200 bytes; open job for full error
bcc960ff assessment-security 💥 KASAN: slab-use-after-free Read in madvise_collapse 2026/06/18 04:37 2026/06/18 04:37 2026/06/18 04:54 b62b3ded 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/3d5252f3447edc39d3...
truncated to first 200 bytes; open job for full error
36ae27cd assessment-security 💥 KASAN: slab-use-after-free Read in madvise_collapse 2026/06/10 00:40 2026/06/10 00:40 2026/06/10 01:01 c36c07f6 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/3d5252f3447edc39d3...
truncated to first 200 bytes; open job for full error
fa026309 assessment-security 💥 KASAN: slab-use-after-free Read in madvise_collapse 2026/06/04 02:42 2026/06/04 02:42 2026/06/04 02:55 62fe1528 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/3d5252f3447edc39d3...
truncated to first 200 bytes; open job for full error
5d07c424 assessment-security 💥 KASAN: slab-use-after-free Read in madvise_collapse 2026/06/01 17:36 2026/06/01 17:36 2026/06/01 17:50 386cc6da 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/3d5252f3447edc39d3...
truncated to first 200 bytes; open job for full error
8d979f77 assessment-security 💥 KASAN: slab-use-after-free Read in madvise_collapse 2026/05/17 05:34 2026/05/17 05:34 2026/05/17 05:54 de5aae85 
failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/3d5252f3447edc39d3...
truncated to first 200 bytes; open job for full error
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[syzbot] [mm?] KASAN: slab-use-after-free Read in madvise_collapse 1 (2) 2023/07/23 22:43
[PATCH v3 10/13 fix] mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock(): fix 1 (1) 2023/07/23 22:32

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in madvise_collapse+0xa6c/0xb50 mm/khugepaged.c:2723
Read of size 8 at addr ffff88802b4e6588 by task syz-executor296/5046

CPU: 0 PID: 5046 Comm: syz-executor296 Not tainted 6.5.0-rc2-next-20230721-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xc4/0x620 mm/kasan/report.c:475
 kasan_report+0xda/0x110 mm/kasan/report.c:588
 madvise_collapse+0xa6c/0xb50 mm/khugepaged.c:2723
 madvise_vma_behavior+0x200/0x1e60 mm/madvise.c:1094
 madvise_walk_vmas+0x1cf/0x2c0 mm/madvise.c:1268
 do_madvise+0x333/0x660 mm/madvise.c:1448
 __do_sys_madvise mm/madvise.c:1461 [inline]
 __se_sys_madvise mm/madvise.c:1459 [inline]
 __x64_sys_madvise+0xaa/0x110 mm/madvise.c:1459
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f7ec298d359
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 51 18 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7ec292d238 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007f7ec2a17318 RCX: 00007f7ec298d359
RDX: 0000000000000019 RSI: 000000000060005f RDI: 0000000020000000
RBP: 00007f7ec2a17310 R08: 00007fffd329edf7 R09: 00007f7ec292d6c0
R10: 0000000000000000 R11: 0000000000000246 R12: b635773f07ebbeea
R13: 000000000000006e R14: 00007fffd329ed10 R15: 00007fffd329edf8
 </TASK>

Allocated by task 5033:
 kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 __kasan_slab_alloc+0x81/0x90 mm/kasan/common.c:328
 kasan_slab_alloc include/linux/kasan.h:186 [inline]
 slab_post_alloc_hook mm/slab.h:762 [inline]
 slab_alloc_node mm/slub.c:3478 [inline]
 slab_alloc mm/slub.c:3486 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3493 [inline]
 kmem_cache_alloc+0x172/0x3b0 mm/slub.c:3502
 vm_area_alloc+0x1f/0x220 kernel/fork.c:485
 mmap_region+0x386/0x2640 mm/mmap.c:2717
 do_mmap+0x87c/0xed0 mm/mmap.c:1353
 vm_mmap_pgoff+0x1a6/0x3b0 mm/util.c:543
 ksys_mmap_pgoff+0x7d/0x5b0 mm/mmap.c:1399
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Freed by task 5035:
 kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:522
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x15e/0x1b0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:162 [inline]
 slab_free_hook mm/slub.c:1800 [inline]
 slab_free_freelist_hook+0x114/0x1e0 mm/slub.c:1826
 slab_free mm/slub.c:3809 [inline]
 kmem_cache_free+0xf0/0x490 mm/slub.c:3831
 rcu_do_batch kernel/rcu/tree.c:2139 [inline]
 rcu_core+0x7fb/0x1bb0 kernel/rcu/tree.c:2403
 __do_softirq+0x218/0x965 kernel/softirq.c:553

Last potentially related work creation:
 kasan_save_stack+0x33/0x50 mm/kasan/common.c:45
 __kasan_record_aux_stack+0xbc/0xd0 mm/kasan/generic.c:492
 __call_rcu_common.constprop.0+0x9a/0x790 kernel/rcu/tree.c:2653
 remove_vma+0x140/0x170 mm/mmap.c:148
 remove_mt mm/mmap.c:2285 [inline]
 do_vmi_align_munmap+0xf75/0x1710 mm/mmap.c:2547
 do_vmi_munmap+0x20e/0x450 mm/mmap.c:2611
 mmap_region+0x194/0x2640 mm/mmap.c:2661
 do_mmap+0x87c/0xed0 mm/mmap.c:1353
 vm_mmap_pgoff+0x1a6/0x3b0 mm/util.c:543
 ksys_mmap_pgoff+0x7d/0x5b0 mm/mmap.c:1399
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

The buggy address belongs to the object at ffff88802b4e6500
 which belongs to the cache vm_area_struct of size 192
The buggy address is located 136 bytes inside of
 freed 192-byte region [ffff88802b4e6500, ffff88802b4e65c0)

The buggy address belongs to the physical page:
page:ffffea0000ad3980 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2b4e6
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000200 ffff888014674b40 ffffea0001dce680 dead000000000002
raw: 0000000000000000 0000000000100010 00000001ffffffff 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 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 4724, tgid 4724 (dhcpcd-run-hook), ts 33134643925, free_ts 33125953991
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x2d2/0x350 mm/page_alloc.c:1569
 prep_new_page mm/page_alloc.c:1576 [inline]
 get_page_from_freelist+0x10d7/0x31b0 mm/page_alloc.c:3256
 __alloc_pages+0x1d0/0x4a0 mm/page_alloc.c:4512
 alloc_pages+0x1a9/0x270 mm/mempolicy.c:2279
 alloc_slab_page mm/slub.c:1870 [inline]
 allocate_slab+0x24e/0x380 mm/slub.c:2017
 new_slab mm/slub.c:2070 [inline]
 ___slab_alloc+0x8bc/0x1570 mm/slub.c:3223
 __slab_alloc.constprop.0+0x56/0xa0 mm/slub.c:3322
 __slab_alloc_node mm/slub.c:3375 [inline]
 slab_alloc_node mm/slub.c:3468 [inline]
 slab_alloc mm/slub.c:3486 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3493 [inline]
 kmem_cache_alloc+0x392/0x3b0 mm/slub.c:3502
 vm_area_alloc+0x1f/0x220 kernel/fork.c:485
 mmap_region+0x386/0x2640 mm/mmap.c:2717
 do_mmap+0x87c/0xed0 mm/mmap.c:1353
 vm_mmap_pgoff+0x1a6/0x3b0 mm/util.c:543
 ksys_mmap_pgoff+0x422/0x5b0 mm/mmap.c:1399
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1160 [inline]
 free_unref_page_prepare+0x508/0xb90 mm/page_alloc.c:2383
 free_unref_page+0x33/0x3b0 mm/page_alloc.c:2478
 vfree+0x181/0x7a0 mm/vmalloc.c:2842
 delayed_vfree_work+0x56/0x70 mm/vmalloc.c:2763
 process_one_work+0xaa2/0x16f0 kernel/workqueue.c:2600
 worker_thread+0x687/0x1110 kernel/workqueue.c:2751
 kthread+0x33a/0x430 kernel/kthread.c:389
 ret_from_fork+0x2c/0x70 arch/x86/kernel/process.c:145
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:296

Memory state around the buggy address:
 ffff88802b4e6480: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
 ffff88802b4e6500: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88802b4e6580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
                      ^
 ffff88802b4e6600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88802b4e6680: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================

Crashes (5):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2023/07/23 09:04 linux-next ae867bc97b71 27cbe77f .config console log report syz C [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in madvise_collapse
2023/07/24 00:30 linux-next ae867bc97b71 27cbe77f .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in madvise_collapse
2023/07/22 17:41 linux-next ae867bc97b71 27cbe77f .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in madvise_collapse
2023/07/18 23:57 linux-next aeba456828b4 022df2bb .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in madvise_collapse
2023/07/18 23:37 linux-next aeba456828b4 022df2bb .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in madvise_collapse
* Struck through repros no longer work on HEAD.