On Thu, Aug 14, 2025 at 7:22 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote:
>
> Drop the restriction for casefold dentries lookup to enable support for
> case-insensitive layers in overlayfs.
>
> Support case-insensitive layers with the condition that they should be
> uniformly enabled across the stack and (i.e. if the root mount dir has
> casefold enabled, so should all the dirs bellow for every layer).
>
> Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> Changes from v4:
> - Move the dentry_weird relaxation to this patch
> - Reword the commit title and message
>
> Changes from v3:
> - New patch, splited from the patch that creates ofs->casefold
> ---
> fs/overlayfs/namei.c | 17 +++++++++--------
> fs/overlayfs/util.c | 8 ++++----
> 2 files changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 76d6248b625e7c58e09685e421aef616aadea40a..e93bcc5727bcafdc18a499b47a7609fd41ecaec8 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -239,13 +239,14 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> char val;
>
> /*
> - * We allow filesystems that are case-folding capable but deny composing
> - * ovl stack from case-folded directories. If someone has enabled case
> - * folding on a directory on underlying layer, the warranty of the ovl
> - * stack is voided.
> + * We allow filesystems that are case-folding capable as long as the
> + * layers are consistently enabled in the stack, enabled for every dir
> + * or disabled in all dirs. If someone has modified case folding on a
> + * directory on underlying layer, the warranty of the ovl stack is
> + * voided.
> */
> - if (ovl_dentry_casefolded(base)) {
> - warn = "case folded parent";
> + if (ofs->casefold != ovl_dentry_casefolded(base)) {
> + warn = "parent wrong casefold";
> err = -ESTALE;
> goto out_warn;
> }
> @@ -259,8 +260,8 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> goto out_err;
> }
>
> - if (ovl_dentry_casefolded(this)) {
> - warn = "case folded child";
> + if (ofs->casefold != ovl_dentry_casefolded(this)) {
> + warn = "child wrong casefold";
> err = -EREMOTE;
> goto out_warn;
> }
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index a33115e7384c129c543746326642813add63f060..7a6ee058568283453350153c1720c35e11ad4d1b 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -210,11 +210,11 @@ bool ovl_dentry_weird(struct dentry *dentry)
> return true;
>
> /*
> - * Allow filesystems that are case-folding capable but deny composing
> - * ovl stack from case-folded directories.
> + * Exceptionally for casefold dentries, we accept that they have their
> + * own hash and compare operations
> */
> - if (sb_has_encoding(dentry->d_sb))
> - return IS_CASEFOLDED(d_inode(dentry));
> + if (ovl_dentry_casefolded(dentry))
> + return false;
>
> return dentry->d_flags & (DCACHE_OP_HASH | DCACHE_OP_COMPARE);
> }
>
> --
> 2.50.1
>
