[Android 6.1] general protection fault in mnt_want_write (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c298d33764cb Revert "ANDROID: add vendor hooks to override..
git tree: android14-6.1
console output: https://syzkaller.appspot.com/x/log.txt?x=177073fa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1a1f62b86d1c1c1
dashboard link: https://syzkaller.appspot.com/bug?extid=e6a450b0aa827202a250
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10f073fa580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=146c979a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c40a40eade8a/disk-c298d337.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/eb78b4e7505f/vmlinux-c298d337.xz
kernel image: https://storage.googleapis.com/syzbot-assets/cf620a0257ca/bzImage-c298d337.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e6a450...@syzkaller.appspotmail.com

incfs: Can't find or create .incomplete dir in ./file0
incfs: mount failed -22
incfs: ino conflict with backing FS 2
general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 1 PID: 377 Comm: syz.2.18 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:mnt_want_write+0x2f/0x300 fs/namespace.c:402
Code: 57 41 56 41 55 41 54 53 50 48 89 fb 49 bd 00 00 00 00 00 fc ff df e8 b0 2f aa ff 48 89 5d d0 4c 8d 73 08 4c 89 f3 48 c1 eb 03 <42> 80 3c 2b 00 74 08 4c 89 f7 e8 02 5c ef ff 4d 8b 3e 4d 8d a7 a8
RSP: 0018:ffffc90000967a68 EFLAGS: 00010202
RAX: ffffffff81c71a10 RBX: 0000000000000001 RCX: ffff8881151e3cc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000967a98 R08: 0000000000000003 R09: 0000000000000004
R10: 0000000000000000 R11: fffff5200012cf2a R12: ffff8881150f1400
R13: dffffc0000000000 R14: 0000000000000008 R15: dffffc0000000000
FS: 000055555fe8a500(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33863fff CR3: 000000012df29000 CR4: 00000000003506a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
ovl_want_write+0x92/0xa0 fs/overlayfs/util.c:22
ovl_setattr+0x9a/0x540 fs/overlayfs/inode.c:33
notify_change+0xcc3/0xf80 fs/attr.c:499
incfs_setattr+0x260/0x3e0 fs/incfs/vfs.c:1688
notify_change+0xcc3/0xf80 fs/attr.c:499
chmod_common+0x223/0x3c0 fs/open.c:607
do_fchmodat+0xd4/0x1a0 fs/open.c:646
__do_sys_chmod fs/open.c:664 [inline]
__se_sys_chmod fs/open.c:662 [inline]
__x64_sys_chmod+0x60/0x70 fs/open.c:662
x64_sys_call+0x760/0x9a0 arch/x86/include/generated/asm/syscalls_64.h:91
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc5e259acb9
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:00007ffff9f5e8f8 EFLAGS: 00000246 ORIG_RAX: 000000000000005a
RAX: ffffffffffffffda RBX: 00007fc5e2815fa0 RCX: 00007fc5e259acb9
RDX: 0000000000000000 RSI: 0000000000000054 RDI: 0000200000000000
RBP: 00007fc5e2608bf7 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc5e2815fac R14: 00007fc5e2815fa0 R15: 00007fc5e2815fa0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:mnt_want_write+0x2f/0x300 fs/namespace.c:402
Code: 57 41 56 41 55 41 54 53 50 48 89 fb 49 bd 00 00 00 00 00 fc ff df e8 b0 2f aa ff 48 89 5d d0 4c 8d 73 08 4c 89 f3 48 c1 eb 03 <42> 80 3c 2b 00 74 08 4c 89 f7 e8 02 5c ef ff 4d 8b 3e 4d 8d a7 a8
RSP: 0018:ffffc90000967a68 EFLAGS: 00010202
RAX: ffffffff81c71a10 RBX: 0000000000000001 RCX: ffff8881151e3cc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000967a98 R08: 0000000000000003 R09: 0000000000000004
R10: 0000000000000000 R11: fffff5200012cf2a R12: ffff8881150f1400
R13: dffffc0000000000 R14: 0000000000000008 R15: dffffc0000000000
FS: 000055555fe8a500(0000) GS:ffff8881f7000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c007056000 CR3: 000000012df29000 CR4: 00000000003506b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
0: 57 push %rdi
1: 41 56 push %r14
3: 41 55 push %r13
5: 41 54 push %r12
7: 53 push %rbx
8: 50 push %rax
9: 48 89 fb mov %rdi,%rbx
c: 49 bd 00 00 00 00 00 movabs $0xdffffc0000000000,%r13
13: fc ff df
16: e8 b0 2f aa ff call 0xffaa2fcb
1b: 48 89 5d d0 mov %rbx,-0x30(%rbp)
1f: 4c 8d 73 08 lea 0x8(%rbx),%r14
23: 4c 89 f3 mov %r14,%rbx
26: 48 c1 eb 03 shr $0x3,%rbx
* 2a: 42 80 3c 2b 00 cmpb $0x0,(%rbx,%r13,1) <-- trapping instruction
2f: 74 08 je 0x39
31: 4c 89 f7 mov %r14,%rdi
34: e8 02 5c ef ff call 0xffef5c3b
39: 4d 8b 3e mov (%r14),%r15
3c: 4d rex.WRB
3d: 8d .byte 0x8d
3e: a7 cmpsl %es:(%rdi),%ds:(%rsi)
3f: a8 .byte 0xa8


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[syzbot]

Bug presence analysis results: the bug reproduces only on Android 6.1.

syzbot has run the reproducer on other relevant kernel trees and got
the following results:

android14-6.1 (commit c298d33764cb) on 2026/01/21:
general protection fault in mnt_want_write
Report: https://syzkaller.appspot.com/x/report.txt?x=17b2f852580000

lts (commit f6e38ae624cf) on 2026/01/21:
Didn't crash.

upstream (commit cf38b2340c0e) on 2026/01/21:
Didn't crash.

More details can be found at:
https://syzkaller.appspot.com/bug?extid=e6a450b0aa827202a250