Re: [Bug] WARNING in vt_do_diacrit in Linux Kernel v6.14

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Jul 08, 2025 at 03:21:36PM +0800, Luka wrote:
> 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.

Where?  I see calls to put_user() happening in that function, and the
return value is properly checked.  What lines exactly show the issue?

> Under conditions such as memory allocation failure or page table
> unavailability, this leads to a fault during execution of the mov
> %eax, (%rcx) instruction.

Again, a normal call to put_user() should be catching this.  Are you
sure you are looking at the latest kernel tree?

> 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.

Please do.

thanks,

greg k-h