[syzbot] [fuse?] general protection fault in fuse_opt_fd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 95c541ddfb08 Add linux-next specific files for 20260316
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16193d52580000
kernel config: https://syzkaller.appspot.com/x/.config?x=bcbfd105f37ac57
dashboard link: https://syzkaller.appspot.com/bug?extid=3c38f696edf9e331cd53
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=10b378da580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16b162d6580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b0922a82fd2b/disk-95c541dd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/869dec734b46/vmlinux-95c541dd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/def78cc5a6eb/bzImage-95c541dd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3c38f6...@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000009: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000048-0x000000000000004f]
CPU: 1 UID: 0 PID: 6045 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:fuse_opt_fd+0x49/0x220 fs/fuse/inode.c:807
Code: 4c 8d bb 98 00 00 00 4c 89 f8 48 c1 e8 03 80 3c 28 00 74 08 4c 89 ff e8 15 f7 e4 fe 4d 8b 3f 4d 8d 66 48 4c 89 e0 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 e7 e8 f9 f6 e4 fe 49 81 3c 24 00 2b 29 8c
RSP: 0018:ffffc90002dd7a68 EFLAGS: 00010206
RAX: 0000000000000009 RBX: ffff88807a954a00 RCX: ffff888031dbdb80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807a954a00
RBP: dffffc0000000000 R08: ffffffff824b518a R09: ffffffff8eb5d6a0
R10: 0000000000000009 R11: 0000000000000000 R12: 0000000000000048
R13: 0000000000000002 R14: 0000000000000000 R15: ffff88801ebe3080
FS: 00005555945e4500(0000) GS:ffff888124ee2000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000003000 CR3: 000000007ae84000 CR4: 00000000003526f0
Call Trace:
<TASK>
fuse_parse_param+0x69b/0xa80 fs/fuse/inode.c:865
vfs_parse_fs_param+0x1a9/0x420 fs/fs_context.c:132
vfs_parse_fs_qstr fs/fs_context.c:173 [inline]
vfs_parse_fs_string include/linux/fs_context.h:142 [inline]
vfs_parse_monolithic_sep+0x283/0x360 fs/fs_context.c:213
do_new_mount+0x304/0xd30 fs/namespace.c:3836
do_mount fs/namespace.c:4173 [inline]
__do_sys_mount fs/namespace.c:4372 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4349
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0932d9c799
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:00007fffbe74bc28 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f0933015fa0 RCX: 00007f0932d9c799
RDX: 0000200000002100 RSI: 00002000000020c0 RDI: 0000000000000000
RBP: 00007f0932e32c99 R08: 0000200000002140 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0933015fac R14: 00007f0933015fa0 R15: 00007f0933015fa0
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:fuse_opt_fd+0x49/0x220 fs/fuse/inode.c:807
Code: 4c 8d bb 98 00 00 00 4c 89 f8 48 c1 e8 03 80 3c 28 00 74 08 4c 89 ff e8 15 f7 e4 fe 4d 8b 3f 4d 8d 66 48 4c 89 e0 48 c1 e8 03 <80> 3c 28 00 74 08 4c 89 e7 e8 f9 f6 e4 fe 49 81 3c 24 00 2b 29 8c
RSP: 0018:ffffc90002dd7a68 EFLAGS: 00010206
RAX: 0000000000000009 RBX: ffff88807a954a00 RCX: ffff888031dbdb80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807a954a00
RBP: dffffc0000000000 R08: ffffffff824b518a R09: ffffffff8eb5d6a0
R10: 0000000000000009 R11: 0000000000000000 R12: 0000000000000048
R13: 0000000000000002 R14: 0000000000000000 R15: ffff88801ebe3080
FS: 00005555945e4500(0000) GS:ffff888124ee2000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000003000 CR3: 000000007ae84000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
0: 4c 8d bb 98 00 00 00 lea 0x98(%rbx),%r15
7: 4c 89 f8 mov %r15,%rax
a: 48 c1 e8 03 shr $0x3,%rax
e: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1)
12: 74 08 je 0x1c
14: 4c 89 ff mov %r15,%rdi
17: e8 15 f7 e4 fe call 0xfee4f731
1c: 4d 8b 3f mov (%r15),%r15
1f: 4d 8d 66 48 lea 0x48(%r14),%r12
23: 4c 89 e0 mov %r12,%rax
26: 48 c1 e8 03 shr $0x3,%rax
* 2a: 80 3c 28 00 cmpb $0x0,(%rax,%rbp,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 4c 89 e7 mov %r12,%rdi
33: e8 f9 f6 e4 fe call 0xfee4f731
38: 49 81 3c 24 00 2b 29 cmpq $0xffffffff8c292b00,(%r12)
3f: 8c


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