[syzbot] KASAN: slab-use-after-free Read in ntfs_show_options

[syzbot] KASAN: slab-use-after-free Read in ntfs_show_options

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    0d8395707651 Merge tag 'soc-fixes-7.2-2' of git://git.kern..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1783bcc6580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cb17729fb04b1e3a
dashboard link: https://syzkaller.appspot.com/bug?extid=4c22f022eb39c86b9d19
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15f877b9580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4c22f022eb39c86b9d19@syzkaller.appspotmail.com

==================================================================
==================================================================
BUG: KASAN: slab-use-after-free in ntfs_show_options+0x656/0x800 fs/ntfs3/super.c:762
Read of size 2 at addr ffff888030028d1c by task syz-executor377/6018

CPU: 0 UID: 0 PID: 6018 Comm: syz-executor377 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 ntfs_show_options+0x656/0x800 fs/ntfs3/super.c:762
 show_vfsmnt+0x637/0x780 fs/proc_namespace.c:129
 seq_read_iter+0x8d6/0xcb0 fs/seq_file.c:273
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x59e/0xa90 fs/read_write.c:574
 ksys_read+0x156/0x270 fs/read_write.c:716
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f12f25c661e
Code: 08 0f 85 f5 e2 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 90 41 57 41 56 4d 89 c6 41 55 4d 89 cd 41 54 55 53 48 83 ec 08
RSP: 002b:00007f12ef560198 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f12ef5616c0 RCX: 00007f12f25c661e
RDX: 0000000000001000 RSI: 00007f12ef560200 RDI: 0000000000000005
RBP: 00007f12f260b03e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f12ef560200
R13: 0000000000000000 R14: 00007fff2ed6d880 R15: 00007fff2ed6d968
 </TASK>

Allocated by task 6027:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x3d2/0x6b0 mm/slub.c:5489
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 ntfs_init_fs_context+0x55/0x570 fs/ntfs3/super.c:1862
 alloc_fs_context+0x9a3/0xd00 fs/fs_context.c:295
 do_remount fs/namespace.c:3392 [inline]
 path_mount+0xc5e/0x1040 fs/namespace.c:4153
 do_mount fs/namespace.c:4174 [inline]
 __do_sys_mount fs/namespace.c:4390 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4367
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6026:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2677 [inline]
 slab_free mm/slub.c:6377 [inline]
 kfree+0x1c5/0x6c0 mm/slub.c:6692
 put_fs_context+0x123/0xb00 fs/fs_context.c:498
 do_remount fs/namespace.c:3419 [inline]
 path_mount+0xef9/0x1040 fs/namespace.c:4153
 do_mount fs/namespace.c:4174 [inline]
 __do_sys_mount fs/namespace.c:4390 [inline]
 __se_sys_mount+0x31d/0x420 fs/namespace.c:4367
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888030028d00
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 28 bytes inside of
 freed 32-byte region [ffff888030028d00, ffff888030028d20)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x30028
flags: 0x80000000000000(node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000000 ffff88813ffb2780 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800400040 00000000f5000000 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 0xd2800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 2774, tgid 2774 (kworker/u8:4), ts 16704250728, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1859
 prep_new_page mm/page_alloc.c:1867 [inline]
 get_page_from_freelist+0x262a/0x26a0 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
 alloc_slab_page mm/slub.c:3266 [inline]
 allocate_slab+0x79/0x5e0 mm/slub.c:3380
 new_slab mm/slub.c:3426 [inline]
 refill_objects+0x2d8/0x350 mm/slub.c:7310
 refill_sheaf mm/slub.c:2804 [inline]
 __pcs_replace_empty_main+0x330/0x690 mm/slub.c:4675
 alloc_from_pcs mm/slub.c:4773 [inline]
 slab_alloc_node mm/slub.c:4905 [inline]
 __kmalloc_cache_noprof+0x468/0x6b0 mm/slub.c:5485
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 slab_free_hook mm/slub.c:2629 [inline]
 slab_free mm/slub.c:6377 [inline]
 kmem_cache_free+0x156/0x6c0 mm/slub.c:6504
 __fput_deferred+0x2df/0x3e0 fs/file_table.c:567
 fput_close+0x11f/0x240 fs/file_table.c:629
 path_openat+0x30d5/0x3850 fs/namei.c:4872
 do_file_open+0x23e/0x4a0 fs/namei.c:4892
 do_open_execat+0x12b/0x590 fs/exec.c:785
 alloc_bprm+0x24/0x640 fs/exec.c:1431
 class_bprm_constructor fs/exec.c:1497 [inline]
 kernel_execve+0x85/0x9c0 fs/exec.c:1889
 call_usermodehelper_exec_async+0x212/0x360 kernel/umh.c:109
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888030028c00: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
 ffff888030028c80: 00 00 00 fc fc fc fc fc fa fb fb fb fc fc fc fc
>ffff888030028d00: fa fb fb fb fc fc fc fc 00 00 04 fc fc fc fc fc
                            ^
 ffff888030028d80: 00 00 07 fc fc fc fc fc 00 00 07 fc fc fc fc fc
 ffff888030028e00: 00 00 00 fc fc fc fc fc 00 00 00 fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] KASAN: slab-use-after-free Read in ntfs_show_options

[Edward Adam Davis]

#syz test: upstream master

diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
index 3305fe406cb2..58540491e68b 100644
--- a/fs/ntfs3/super.c
+++ b/fs/ntfs3/super.c
@@ -461,7 +461,7 @@ static int ntfs_fs_reconfigure(struct fs_context *fc)
 	}
 
 	sync_filesystem(sb);
-	swap(sbi->options, fc->fs_private);
+	memcpy(sbi->options, fc->fs_private, sizeof(*sbi->options));
 
 	return 0;
 }

Re: [syzbot] KASAN: slab-use-after-free Read in ntfs_show_options

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+4c22f022eb39c86b9d19@syzkaller.appspotmail.com
Tested-by: syzbot+4c22f022eb39c86b9d19@syzkaller.appspotmail.com

Tested on:

commit:         06cf6189 Merge tag 'x86-urgent-2026-08-08' of git://gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1735e132580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6ddb3079499f48cb
dashboard link: https://syzkaller.appspot.com/bug?extid=4c22f022eb39c86b9d19
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=143fbfb9580000

Note: testing is done by a robot and is best-effort only.

[PATCH] ntfs3: Update only the member values without replacing the opts pointer

[Edward Adam Davis]

There is a potential race condition when accessing options during remount
and read operations. This would trigger a uaf [1].

CPU0: remount				CPU1: read options
==================================	==================
do_remount()
reconfigure_super()
 ntfs_fs_reconfigure()
  sbi->options = fc->fs_private
put_fs_context()
 ntfs_fs_free()
  put_mount_options()			ntfs_show_options()
   kfree(sbi->options)			 opts = sbi->options
				         opts->dmask //trigger uaf

The fix involves not updating the sbi->options pointer during
reconfiguration, but instead using fc->fs_private to update the
corresponding member values.

[1]
BUG: KASAN: slab-use-after-free in ntfs_show_options+0x656/0x800 fs/ntfs3/super.c:762
Call Trace:
 ntfs_show_options+0x656/0x800 fs/ntfs3/super.c:762
 show_vfsmnt+0x637/0x780 fs/proc_namespace.c:129
 seq_read_iter+0x8d6/0xcb0 fs/seq_file.c:273
 new_sync_read fs/read_write.c:493 [inline]
 vfs_read+0x59e/0xa90 fs/read_write.c:574

Allocated by task 6027:
 ntfs_init_fs_context+0x55/0x570 fs/ntfs3/super.c:1862
 alloc_fs_context+0x9a3/0xd00 fs/fs_context.c:295
 do_remount fs/namespace.c:3392 [inline]
 path_mount+0xc5e/0x1040 fs/namespace.c:4153
 do_mount fs/namespace.c:4174 [inline]

Freed by task 6026:
 kfree+0x1c5/0x6c0 mm/slub.c:6692
 put_fs_context+0x123/0xb00 fs/fs_context.c:498
 do_remount fs/namespace.c:3419 [inline]
 path_mount+0xef9/0x1040 fs/namespace.c:4153
 do_mount fs/namespace.c:4174 [inline]

Fixes: cd39981fb92a ("fs/ntfs3: Fix double free on remount")
Reported-by: syzbot+4c22f022eb39c86b9d19@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4c22f022eb39c86b9d19
Tested-by: syzbot+4c22f022eb39c86b9d19@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/ntfs3/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
index 3305fe406cb2..58540491e68b 100644
--- a/fs/ntfs3/super.c
+++ b/fs/ntfs3/super.c
@@ -461,7 +461,7 @@ static int ntfs_fs_reconfigure(struct fs_context *fc)
 	}
 
 	sync_filesystem(sb);
-	swap(sbi->options, fc->fs_private);
+	memcpy(sbi->options, fc->fs_private, sizeof(*sbi->options));
 
 	return 0;
 }
-- 
2.43.0