linux-kernel - Re: [PATCH 1/5] fs/filesystems: Fix potential unsigned integer underflow in fs

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Message-ID: <2425260.1744385645@warthog.procyon.org.uk>
Date: Fri, 11 Apr 2025 16:34:05 +0100
From: David Howells <dhowells@...hat.com>
To: Zijun Hu <zijun_hu@...oud.com>
Cc: dhowells@...hat.com, Alexander Viro <viro@...iv.linux.org.uk>,
    Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
    linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
    Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH 1/5] fs/filesystems: Fix potential unsigned integer underflow in fs_name()

Zijun Hu <zijun_hu@...oud.com> wrote:

> fs_name() has @index as unsigned int, so there is underflow risk for
> operation '@...ex--'.
> 
> Fix by breaking the for loop when '@...ex == 0' which is also more proper
> than '@...ex <= 0' for unsigned integer comparison.

There isn't really a risk.  The list walked by "tmp" and the checks that this
is or is not NULL will prevent a problem.

I also feel that breaking out of the loop with "<= 0" - even if the variable
is unsigned - is safer, on the off chance that someone in the future changes
the signedness of the variable.

David