linux-ext4 - Re: [PATCH v3 08/16] xfs: Report case sensitivity in fileattr

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

Message-ID: <20260113160223.GA15522@frogsfrogsfrogs>
Date: Tue, 13 Jan 2026 08:02:23 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: Chuck Lever <cel@...nel.org>
Cc: vira@....codeaurora.org, Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
	linux-cifs@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net, hirofumi@...l.parknet.co.jp,
	linkinjeon@...nel.org, sj1557.seo@...sung.com, yuezhang.mo@...y.com,
	almaz.alexandrovich@...agon-software.com, slava@...eyko.com,
	glaubitz@...sik.fu-berlin.de, frank.li@...o.com, tytso@....edu,
	adilger.kernel@...ger.ca, cem@...nel.org, sfrench@...ba.org,
	pc@...guebit.org, ronniesahlberg@...il.com, sprasad@...rosoft.com,
	trondmy@...nel.org, anna@...nel.org, jaegeuk@...nel.org,
	chao@...nel.org, hansg@...nel.org, senozhatsky@...omium.org,
	Chuck Lever <chuck.lever@...cle.com>, Neal Gompa <neal@...pa.dev>
Subject: Re: [PATCH v3 08/16] xfs: Report case sensitivity in fileattr_get

On Mon, Jan 12, 2026 at 12:46:21PM -0500, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@...cle.com>
> 
> Upper layers such as NFSD need to query whether a filesystem is
> case-sensitive. Populate the case_insensitive and case_preserving
> fields in xfs_fileattr_get(). XFS always preserves case. XFS is
> case-sensitive by default, but supports ASCII case-insensitive
> lookups when formatted with the ASCIICI feature flag.
> 
> Signed-off-by: Chuck Lever <chuck.lever@...cle.com>

Well as a pure binary statement of xfs' capabilities, this is correct so:
Reviewed-by: "Darrick J. Wong" <djwong@...nel.org>

[add ngompa]

But the next obvious question I would have as a userspace programmer is
"case insensitive how, exactly?", which was the topic of the previous
revision.  Somewhere out there there's a program / emulation layer that
will want to know the exact transformation when doing a non-memcmp
lookup.  Probably Winderz casefolding has behaved differently every
release since the start of NTFS, etc.

I don't know how to solve that, other than the fs compiles its
case-flattening code into a bpf program and exports that where someone
can read() it and run/analyze/reverse engineer it.  But ugh, Linus is
right that this area is a mess. :/

--D

> ---
>  fs/xfs/xfs_ioctl.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 59eaad774371..97314fcb7732 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -516,6 +516,13 @@ xfs_fileattr_get(
>  	xfs_fill_fsxattr(ip, XFS_DATA_FORK, fa);
>  	xfs_iunlock(ip, XFS_ILOCK_SHARED);
>  
> +	/*
> +	 * XFS is case-sensitive by default, but can be formatted with
> +	 * ASCII case-insensitive mode enabled.
> +	 */
> +	fa->case_insensitive = xfs_has_asciici(ip->i_mount);
> +	fa->case_preserving = true;
> +
>  	return 0;
>  }
>  
> -- 
> 2.52.0
> 
>