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Thu, 05 Nov 2026 23:35:40 -0800 (PST) Date: Thu, 05 Nov 2026 23:35:40 -0800 X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6aed834c.dadc8e63.45095.0003.GAE@google.com> Subject: [syzbot] [usb?] general protection fault in mct_u232_open From: syzbot To: gregkh@linuxfoundation.org, johan@kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" Hello, syzbot found the following issue on: HEAD commit: ddfe51b0a0f5 Add linux-next specific files for 20261105 git tree: linux-next console+strace: https://syzkaller.appspot.com/x/log.txt?x=12627abe580000 kernel config: https://syzkaller.appspot.com/x/.config?x=3dffa811bfeed6b4 dashboard link: https://syzkaller.appspot.com/bug?extid=58b2d8b19cd6761a395b compiler: Debian clang version 22.1.8 (1~deb13u4), Debian LLD 22.1.8 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14f5f2be580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16627abe580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/181043a4bd52/disk-ddfe51b0.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/a69d8b670c38/vmlinux-ddfe51b0.xz kernel image: https://storage.googleapis.com/syzbot-assets/906d515c0893/bzImage-ddfe51b0.xz AI-generated root cause summary: In mct_u232_open(), if submitting the read URB via usb_submit_urb(priv->read_urb, GFP_KERNEL) fails, the driver logs an error message referencing port->read_urb->pipe instead of priv->read_urb->pipe. Because the MCT U232 adapter uses interrupt-in endpoints instead of bulk-in endpoints, port->read_urb is never allocated or set up by the usb-serial core and remains NULL. Dereferencing port->read_urb->pipe in the error path results in a NULL-pointer dereference at offset 0x50 (the offset of the pipe field in struct urb), crashing the kernel with an oops. full analysis: https://syzkaller.appspot.com/x/ai_root_cause?x=58b2d8b19cd6761a395b IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+58b2d8b19cd6761a395b@syzkaller.appspotmail.com mct_u232 ttyUSB0: Set MODEM CTRL 0xb failed (error = -71) mct_u232 ttyUSB0: Set LINE CTRL 0x3 failed (error = -71) mct_u232 ttyUSB0: Get MODEM STATus failed (error = -19) Oops: general protection fault, probably for non-canonical address 0xdffffc000000000a: 0000 [#1] SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057] CPU: 0 UID: 0 PID: 5718 Comm: syz-executor711 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026 RIP: 0010:mct_u232_open+0x39c/0x680 drivers/usb/serial/mct_u232.c:460 Code: 8d 9e 20 04 00 00 48 89 d8 48 c1 e8 03 42 80 3c 38 00 74 08 48 89 df e8 62 c3 6e fa 48 8b 1b 48 83 c3 50 48 89 d8 48 c1 e8 03 <42> 0f b6 04 38 84 c0 0f 85 a7 01 00 00 8b 13 49 81 c6 40 05 00 00 RSP: 0018:ffffc90003b7f760 EFLAGS: 00010206 RAX: 000000000000000a RBX: 0000000000000050 RCX: ffff88802e889f40 RDX: 0000000000000000 RSI: 00000000ffffffed RDI: 0000000000000000 RBP: 00000000ffffffed R08: ffffffff91e120bf R09: 1ffffffff23c2417 R10: dffffc0000000000 R11: fffffbfff23c2418 R12: 1ffff11005c8bf50 R13: dffffc0000000000 R14: ffff888034df4000 R15: dffffc0000000000 FS: 0000555579e9e400(0000) GS:ffff888123159000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f2cf0c571bc CR3: 0000000037ff2000 CR4: 00000000003526f0 Call Trace: serial_port_activate+0x151/0x250 drivers/usb/serial/usb-serial.c:268 tty_port_open+0x1df/0x2d0 drivers/tty/tty_port.c:798 tty_open+0x48a/0xd80 drivers/tty/tty_io.c:2112 chrdev_open+0x4d9/0x600 fs/char_dev.c:413 do_dentry_open+0x80e/0x1360 fs/open.c:1000 vfs_open_consume+0x4a/0x350 fs/open.c:1131 do_open fs/namei.c:4851 [inline] path_openat+0x16fc/0x20f0 fs/namei.c:5016 do_file_open+0x23e/0x4a0 fs/namei.c:5045 do_sys_openat2+0x115/0x200 fs/open.c:1443 do_sys_open fs/open.c:1449 [inline] __do_sys_openat fs/open.c:1789 [inline] __se_sys_openat fs/open.c:1784 [inline] __x64_sys_openat+0x138/0x170 fs/open.c:1784 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline] do_syscall_64+0x16a/0x530 arch/x86/entry/syscall_64.c:89 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x00007f2cf0bf0079 Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffe3866ad58 EFLAGS: 00000246 ORIG_RAX: 0000000000000101 RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f2cf0bf0079 RDX: 0000000000000000 RSI: 0000200000000200 RDI: 00000000ffffff9c RBP: 00000000000f4240 R08: 0000000000000009 R09: 0000000000000009 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000014f37 R13: 00007ffe3866ad6c R14: 00007ffe3866ad80 R15: 00007ffe3866ad70 Modules linked in: ---[ end trace 0000000000000000 ]--- RIP: 0010:mct_u232_open+0x39c/0x680 drivers/usb/serial/mct_u232.c:460 Code: 8d 9e 20 04 00 00 48 89 d8 48 c1 e8 03 42 80 3c 38 00 74 08 48 89 df e8 62 c3 6e fa 48 8b 1b 48 83 c3 50 48 89 d8 48 c1 e8 03 <42> 0f b6 04 38 84 c0 0f 85 a7 01 00 00 8b 13 49 81 c6 40 05 00 00 RSP: 0018:ffffc90003b7f760 EFLAGS: 00010206 RAX: 000000000000000a RBX: 0000000000000050 RCX: ffff88802e889f40 RDX: 0000000000000000 RSI: 00000000ffffffed RDI: 0000000000000000 RBP: 00000000ffffffed R08: ffffffff91e120bf R09: 1ffffffff23c2417 R10: dffffc0000000000 R11: fffffbfff23c2418 R12: 1ffff11005c8bf50 R13: dffffc0000000000 R14: ffff888034df4000 R15: dffffc0000000000 FS: 0000555579e9e400(0000) GS:ffff888123159000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f2cf0c92680 CR3: 0000000037ff2000 CR4: 00000000003526f0 ---------------- Code disassembly (best guess): 0: 8d 9e 20 04 00 00 lea 0x420(%rsi),%ebx 6: 48 89 d8 mov %rbx,%rax 9: 48 c1 e8 03 shr $0x3,%rax d: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1) 12: 74 08 je 0x1c 14: 48 89 df mov %rbx,%rdi 17: e8 62 c3 6e fa call 0xfa6ec37e 1c: 48 8b 1b mov (%rbx),%rbx 1f: 48 83 c3 50 add $0x50,%rbx 23: 48 89 d8 mov %rbx,%rax 26: 48 c1 e8 03 shr $0x3,%rax * 2a: 42 0f b6 04 38 movzbl (%rax,%r15,1),%eax <-- trapping instruction 2f: 84 c0 test %al,%al 31: 0f 85 a7 01 00 00 jne 0x1de 37: 8b 13 mov (%rbx),%edx 39: 49 81 c6 40 05 00 00 add $0x540,%r14 --- 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