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KASAN: slab-use-after-free Read in ext4_ext_remove_space

Status: moderation: reported on 2025/02/27 09:06
Subsystems: ext4
[Documentation on labels]
Reported-by: syzbot+1f412d05048013188bc9@syzkaller.appspotmail.com
First crash: 4d13h, last: 4d04h
▶ ▼ Similar bugs (6)
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: out-of-bounds Read in ext4_ext_remove_space origin:upstream missing-backport C error error 7 41d 573d 0/2 upstream: reported C repro on 2023/08/04 22:38
android-5-10 KASAN: out-of-bounds Read in ext4_ext_remove_space C error 3 23d 544d 0/2 upstream: reported C repro on 2023/09/02 13:17
upstream KASAN: out-of-bounds Read in ext4_ext_remove_space ext4 C error done 8 420d 594d 25/28 fixed on 2024/02/16 19:40
android-6-1 KASAN: out-of-bounds Read in ext4_ext_remove_space missing-backport C error error 6 131d 563d 0/2 auto-obsoleted due to no activity on 2025/01/27 17:01
linux-5.15 KASAN: out-of-bounds Read in ext4_ext_remove_space origin:upstream missing-backport C done 5 62d 403d 0/3 upstream: reported C repro on 2024/01/21 16:07
linux-6.1 KASAN: out-of-bounds Read in ext4_ext_remove_space origin:upstream missing-backport C done 4 194d 421d 0/3 upstream: reported C repro on 2024/01/03 15:27

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in ext4_ext_rm_leaf fs/ext4/extents.c:2623 [inline]
BUG: KASAN: slab-use-after-free in ext4_ext_remove_space+0x2ce0/0x4058 fs/ext4/extents.c:2961
Read of size 4 at addr ffff0000dae2c4c8 by task syz.3.297/8071

CPU: 0 UID: 0 PID: 8071 Comm: syz.3.297 Not tainted 6.14.0-rc3-syzkaller-ga1c24ab82279 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:466 (C)
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0xe4/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x198/0x538 mm/kasan/report.c:489
 kasan_report+0xd8/0x138 mm/kasan/report.c:602
 __asan_report_load4_noabort+0x20/0x2c mm/kasan/report_generic.c:380
 ext4_ext_rm_leaf fs/ext4/extents.c:2623 [inline]
 ext4_ext_remove_space+0x2ce0/0x4058 fs/ext4/extents.c:2961
 ext4_ext_truncate+0x134/0x1d4 fs/ext4/extents.c:4466
 ext4_truncate+0x9dc/0x10ac fs/ext4/inode.c:4217
 ext4_setattr+0xdc8/0x173c fs/ext4/inode.c:5542
 notify_change+0x9f0/0xca0 fs/attr.c:552
 do_truncate+0x1c0/0x28c fs/open.c:65
 handle_truncate fs/namei.c:3451 [inline]
 do_open fs/namei.c:3834 [inline]
 path_openat+0x249c/0x2b1c fs/namei.c:3989
 do_filp_open+0x1e8/0x404 fs/namei.c:4016
 do_sys_openat2+0x124/0x1b8 fs/open.c:1428
 do_sys_open fs/open.c:1443 [inline]
 __do_sys_openat fs/open.c:1459 [inline]
 __se_sys_openat fs/open.c:1454 [inline]
 __arm64_sys_openat+0x1f0/0x240 fs/open.c:1454
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:744
 el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:762
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

Allocated by task 6060:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:68
 kasan_save_alloc_info+0x40/0x50 mm/kasan/generic.c:562
 unpoison_slab_object mm/kasan/common.c:319 [inline]
 __kasan_slab_alloc+0x74/0x8c mm/kasan/common.c:345
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4115 [inline]
 slab_alloc_node mm/slub.c:4164 [inline]
 kmem_cache_alloc_noprof+0x254/0x410 mm/slub.c:4171
 getname_flags+0xcc/0x4b4 fs/namei.c:139
 do_readlinkat+0xbc/0x4d4 fs/stat.c:563
 __do_sys_readlinkat fs/stat.c:595 [inline]
 __se_sys_readlinkat fs/stat.c:592 [inline]
 __arm64_sys_readlinkat+0x9c/0xb8 fs/stat.c:592
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:744
 el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:762
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

Freed by task 6060:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:68
 kasan_save_free_info+0x54/0x6c mm/kasan/generic.c:576
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x64/0x8c mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2353 [inline]
 slab_free mm/slub.c:4609 [inline]
 kmem_cache_free+0x198/0x554 mm/slub.c:4711
 putname+0x130/0x184 fs/namei.c:296
 do_readlinkat+0x25c/0x4d4 fs/stat.c:584
 __do_sys_readlinkat fs/stat.c:595 [inline]
 __se_sys_readlinkat fs/stat.c:592 [inline]
 __arm64_sys_readlinkat+0x9c/0xb8 fs/stat.c:592
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:744
 el0t_64_sync_handler+0x84/0x108 arch/arm64/kernel/entry-common.c:762
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:600

The buggy address belongs to the object at ffff0000dae2c400
 which belongs to the cache names_cache of size 4096
The buggy address is located 200 bytes inside of
 freed 4096-byte region [ffff0000dae2c400, ffff0000dae2d400)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11ae28
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x5ffc00000000040(head|node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000040 ffff0000c18a88c0 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000070007 00000000f5000000 0000000000000000
head: 05ffc00000000040 ffff0000c18a88c0 dead000000000122 0000000000000000
head: 0000000000000000 0000000000070007 00000000f5000000 0000000000000000
head: 05ffc00000000003 fffffdffc36b8a01 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000dae2c380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff0000dae2c400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000dae2c480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff0000dae2c500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000dae2c580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/02/23 08:59 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci a1c24ab82279 d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 KASAN: slab-use-after-free Read in ext4_ext_remove_space
2025/02/23 18:28 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci a1c24ab82279 d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 KASAN: use-after-free Read in ext4_ext_remove_space
* Struck through repros no longer work on HEAD.