On Fri, Aug 8, 2025 at 10:59 PM André Almeida <andrealmeid@xxxxxxxxxx> wrote:
>
> Drop the restriction for casefold dentries to enable support for
> case-insensitive filesystems in overlayfs.
>
> Support case-insensitive filesystems with the condition that they should
> be uniformly enabled across the stack and the layers (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>
> ---
> Changes from v2:
> - Create new ovl_fs flag, bool casefold
> - Check if casefolded dentry is consistent with the root dentry
> ---
> fs/overlayfs/namei.c | 17 +++++++++--------
> fs/overlayfs/ovl_entry.h | 1 +
> fs/overlayfs/params.c | 7 ++-----
> fs/overlayfs/util.c | 8 ++++----
> 4 files changed, 16 insertions(+), 17 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 76d6248b625e7c58e09685e421aef616aadea40a..08b34e52b36f93d4da09e4d13b51d23dc99ca6d6 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 enabled case folding on a
If someone has modified case folding....
> + * 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/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 4c1bae935ced274f93a0d23fe10d34455e226ec4..1d4828dbcf7ac4ba9657221e601bbf79d970d225 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -91,6 +91,7 @@ struct ovl_fs {
> struct mutex whiteout_lock;
> /* r/o snapshot of upperdir sb's only taken on volatile mounts */
> errseq_t errseq;
> + bool casefold;
Better introduce this in an earlier patch, even if it is only set in the
last patch, so that other code can use it, like the inode S_CASEFOLD
assertion.
> };
>
> /* Number of lower layers, not including data-only layers */
> diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
> index f4e7fff909ac49e2f8c58a76273426c1158a7472..afa1c29515a9729bfe88c8166da4aefa6cddc5a5 100644
> --- a/fs/overlayfs/params.c
> +++ b/fs/overlayfs/params.c
> @@ -277,16 +277,13 @@ static int ovl_mount_dir_check(struct fs_context *fc, const struct path *path,
> enum ovl_opt layer, const char *name, bool upper)
> {
> struct ovl_fs_context *ctx = fc->fs_private;
> + struct ovl_fs *ovl = fc->s_fs_info;
ofs, not ovl
>
> if (!d_is_dir(path->dentry))
> return invalfc(fc, "%s is not a directory", name);
>
> - /*
> - * Allow filesystems that are case-folding capable but deny composing
> - * ovl stack from case-folded directories.
> - */
> if (ovl_dentry_casefolded(path->dentry))
> - return invalfc(fc, "case-insensitive directory on %s not supported", name);
> + ovl->casefold = true;
>
The problem with removing this invalf() is that it is more useful to userspace
than the kernel logs in ovl_fill_supper(), so I prefer to leave this descriptive
configuration error here, something like this:
diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c
index f4e7fff909ac..57035f0f594e 100644
--- a/fs/overlayfs/params.c
+++ b/fs/overlayfs/params.c
@@ -277,16 +277,24 @@ static int ovl_mount_dir_check(struct fs_context
*fc, const struct path *path,
enum ovl_opt layer, const char *name, bool upper)
{
struct ovl_fs_context *ctx = fc->fs_private;
+ struct ovl_fs *ofs = fc->s_fs_info;
+ bool is_casefolded = ovl_dentry_casefolded(path->dentry);
if (!d_is_dir(path->dentry))
return invalfc(fc, "%s is not a directory", name);
/*
* Allow filesystems that are case-folding capable but deny composing
- * ovl stack from case-folded directories.
+ * ovl stack from inconsistent case-folded directories.
*/
- if (ovl_dentry_casefolded(path->dentry))
- return invalfc(fc, "case-insensitive directory on %s
not supported", name);
+ if (!ctx->casefold_set) {
+ ofs->casefold = is_casefolded;
+ ctx->casefold_set = true;
+ }
+ if (ofs->casefold != is_casefolded)
+ return invalfc(fc, "case-%ssensitive directory on %s
is inconsistent",
+ is_casefolded ? "in" : "", name);
+ }
if (ovl_dentry_weird(path->dentry))
return invalfc(fc, "filesystem on %s not supported", name);
diff --git a/fs/overlayfs/params.h b/fs/overlayfs/params.h
index c96d93982021..ffd53cdd8482 100644
--- a/fs/overlayfs/params.h
+++ b/fs/overlayfs/params.h
@@ -33,6 +33,7 @@ struct ovl_fs_context {
struct ovl_opt_set set;
struct ovl_fs_context_layer *lower;
char *lowerdir_all; /* user provided lowerdir string */
+ bool casefold_set;
};
Thanks,
Amir.
