linux-kernel - Re: [PATCH] fs: exfat: fix improper check of dentry.stream.valid

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Message-ID: <CAKYAXd-OSYg3fVoxDKVQm6r2kQDJuR-UfL26_ijoCPMsxX=L8Q@mail.gmail.com>
Date: Wed, 15 Oct 2025 14:39:42 +0900
From: Namjae Jeon <linkinjeon@...nel.org>
To: Jaehun Gou <p22gone@...il.com>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Seunghun Han <kkamagui@...il.com>, Jihoon Kwon <jimmyxyz010315@...il.com>
Subject: Re: [PATCH] fs: exfat: fix improper check of dentry.stream.valid_size

On Tue, Oct 14, 2025 at 10:02 PM Jaehun Gou <p22gone@...il.com> wrote:
>
> We found an infinite loop bug in the exFAT file system that can lead to a
> Denial-of-Service (DoS) condition. When a dentry in an exFAT filesystem is
> malformed, the following system calls — SYS_openat, SYS_ftruncate, and
> SYS_pwrite64 — can cause the kernel to hang.
>
> Root cause analysis shows that the size validation code in exfat_find()
> does not check whether dentry.stream.valid_size is negative. As a result,
> the system calls mentioned above can succeed and eventually trigger the DoS
> issue.
>
> This patch adds a check for negative dentry.stream.valid_size to prevent
> this vulnerability.
>
> Co-developed-by: Seunghun Han <kkamagui@...il.com>
> Signed-off-by: Seunghun Han <kkamagui@...il.com>
> Co-developed-by: Jihoon Kwon <jimmyxyz010315@...il.com>
> Signed-off-by: Jihoon Kwon <jimmyxyz010315@...il.com>
> Signed-off-by: Jaehun Gou <p22gone@...il.com>
Applied it to #dev.
Thanks!