linux-kernel - Re: [PATCH v2] exfat: fix out-of-bounds in exfat_nls_to

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAKYAXd_2VUniUHgstfATfdjDfLokqfjCGm+P=_72EPM2HEi0Ew@mail.gmail.com>
Date: Sat, 11 Oct 2025 14:40:36 +0900
From: Namjae Jeon <linkinjeon@...nel.org>
To: Jeongjun Park <aha310510@...il.com>
Cc: Sungjong Seo <sj1557.seo@...sung.com>, Yuezhang Mo <yuezhang.mo@...y.com>, 
	Al Viro <viro@...iv.linux.org.uk>, pali@...nel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
	syzbot+98cc76a76de46b3714d4@...kaller.appspotmail.com
Subject: Re: [PATCH v2] exfat: fix out-of-bounds in exfat_nls_to_ucs2()

On Fri, Oct 10, 2025 at 2:04 PM Jeongjun Park <aha310510@...il.com> wrote:
>
> In exfat_nls_to_ucs2(), if there is no NLS loss and the char-to-ucs2
> conversion is successfully completed, the variable "i" will have the same
> value as len.
>
> However, exfat_nls_to_ucs2() checks p_cstring[i] to determine whether nls
> is lost immediately after the while loop ends, so if len is FSLABEL_MAX,
> "i" will also be FSLABEL_MAX immediately after the while loop ends,
> resulting in an out-of-bounds read of 1 byte from the p_cstring stack
> memory.
>
> Therefore, to prevent this and properly determine whether nls has been
> lost, it should be modified to check if "i" and len are equal, rather than
> dereferencing p_cstring.
>
> Cc: <stable@...r.kernel.org>
> Reported-by: syzbot+98cc76a76de46b3714d4@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=98cc76a76de46b3714d4
> Fixes: 370e812b3ec1 ("exfat: add nls operations")
> Signed-off-by: Jeongjun Park <aha310510@...il.com>
> ---
>  fs/exfat/nls.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/exfat/nls.c b/fs/exfat/nls.c
> index 8243d94ceaf4..de06abe426d7 100644
> --- a/fs/exfat/nls.c
> +++ b/fs/exfat/nls.c
> @@ -616,7 +616,7 @@ static int exfat_nls_to_ucs2(struct super_block *sb,
>                 unilen++;
>         }
>
> -       if (p_cstring[i] != '\0')
> +       if (i != len)
>                 lossy |= NLS_NAME_OVERLEN;
As I said before, the core problem is passing an incorrect length in the ioctl
FS_IOC_SETFSLABEL call. While your change may fix the symptom,
it doesn't fix the root cause.
Furthermore, NLS_NAME_OVERLEN macro is unnecessary.
That will result in different errors when creating a file with trailing periods
with utf8 and the other iocharset.
Please remove it and make the same error handling for maximum length
consistent with exfat_utf8_to_utf16().

>
>         *uniname = '\0';
> --