linux-kernel - [Bug] WARNING in vt_do_diacrit in Linux Kernel v6.14

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Message-ID: <CALm_T+2AUcGgb+ukfGg5a3=ibQzRe93gHAzjh6XUubCePk=Mig@mail.gmail.com>
Date: Tue, 8 Jul 2025 15:21:36 +0800
From: Luka <luka.2016.cs@...il.com>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: [Bug] WARNING in vt_do_diacrit in Linux Kernel v6.14

Dear Linux Kernel Maintainers,

I hope this message finds you well.

I am writing to report a potential vulnerability I encountered during
testing of the Linux Kernel version v6.14.

Git Commit: 38fec10eb60d687e30c8c6b5420d86e8149f7557 (tag: v6.14)

Bug Location: drivers/tty/vt/keyboard.c

Bug report: https://pastebin.com/yuVJpati

Complete log: https://pastebin.com/qKnipvvK

Entire kernel config: https://pastebin.com/MRWGr3nv

Root Cause Analysis:
The vt_do_diacrit() function in the virtual terminal subsystem
performs a write to a user-space pointer via __put_user_4() without
ensuring that the destination address is mapped and accessible.
Under conditions such as memory allocation failure or page table
unavailability, this leads to a fault during execution of the mov
%eax, (%rcx) instruction.

At present, I have not yet obtained a minimal reproducer for this
issue. However, I am actively working on reproducing it, and I will
promptly share any additional findings or a working reproducer as soon
as it becomes available.

Thank you very much for your time and attention to this matter. I
truly appreciate the efforts of the Linux kernel community.

Best regards,
Luka