Case folding is often applied to subtrees and not on an entire filesystem. Disallowing layers from filesystems that support case folding is over limiting. Replace the rule that case-folding capable are not allowed as layers with a rule that case folded directories are not allowed in a merged directory stack. Should case folding be enabled on an underlying directory while overlayfs is mounted the outcome is generally undefined. Specifically in ovl_lookup(), we check the base underlying directory and fail with -ESTALE and write a warning to kmsg if an underlying directory case folding is enabled. Suggested-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> Link: https://lore.kernel.org/linux-fsdevel/20250520051600.1903319-1-kent.overstreet@xxxxxxxxx/ Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx> --- Miklos, This is my solution to Kent's request to allow overlayfs mount on bcachefs subtrees that do not have casefolding enabled, while other subtrees do have casefolding enabled. I have written a test to cover the change of behavior [1]. This test does not run on old kernel's where the mount always fails with casefold capable layers. Let me know what you think. Kent, I have tested this on ext4. Please test on bcachefs. Thanks, Amir. Changes since v1,v2: - Add ratelimited warnings for the lookup error cases - Add helper ovl_dentry_casefolded() - Write fstest [1] [1] https://github.com/amir73il/xfstests/commits/ovl-casefold/ fs/overlayfs/namei.c | 31 ++++++++++++++++++++++++++++--- fs/overlayfs/overlayfs.h | 6 ++++++ fs/overlayfs/params.c | 10 ++++------ fs/overlayfs/util.c | 15 +++++++++++---- 4 files changed, 49 insertions(+), 13 deletions(-) diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c index d489e80feb6f..733beef7b810 100644 --- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -230,13 +230,26 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d, struct dentry **ret, bool drop_negative) { struct ovl_fs *ofs = OVL_FS(d->sb); - struct dentry *this; + struct dentry *this = NULL; + const char *warn; struct path path; int err; bool last_element = !post[0]; bool is_upper = d->layer->idx == 0; 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. + */ + if (ovl_dentry_casefolded(base)) { + warn = "case folded parent"; + err = -ESTALE; + goto out_warn; + } + this = ovl_lookup_positive_unlocked(d, name, base, namelen, drop_negative); if (IS_ERR(this)) { err = PTR_ERR(this); @@ -246,10 +259,17 @@ 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"; + err = -EREMOTE; + goto out_warn; + } + if (ovl_dentry_weird(this)) { /* Don't support traversing automounts and other weirdness */ + warn = "unsupported object type"; err = -EREMOTE; - goto out_err; + goto out_warn; } path.dentry = this; @@ -283,8 +303,9 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d, } else { if (ovl_lookup_trap_inode(d->sb, this)) { /* Caught in a trap of overlapping layers */ + warn = "overlapping layers"; err = -ELOOP; - goto out_err; + goto out_warn; } if (last_element) @@ -316,6 +337,10 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d, this = NULL; goto out; +out_warn: + pr_warn_ratelimited("failed lookup in %s (%pd2, name='%.*s', err=%i): %s\n", + is_upper ? "upper" : "lower", base, + namelen, name, err, warn); out_err: dput(this); return err; diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index aef942a758ce..6c51103d9305 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -446,6 +446,12 @@ void ovl_dentry_init_reval(struct dentry *dentry, struct dentry *upperdentry, void ovl_dentry_init_flags(struct dentry *dentry, struct dentry *upperdentry, struct ovl_entry *oe, unsigned int mask); bool ovl_dentry_weird(struct dentry *dentry); + +static inline bool ovl_dentry_casefolded(struct dentry *dentry) +{ + return sb_has_encoding(dentry->d_sb) && IS_CASEFOLDED(d_inode(dentry)); +} + enum ovl_path_type ovl_path_type(struct dentry *dentry); void ovl_path_upper(struct dentry *dentry, struct path *path); void ovl_path_lower(struct dentry *dentry, struct path *path); diff --git a/fs/overlayfs/params.c b/fs/overlayfs/params.c index f42488c01957..2b9b31524c38 100644 --- a/fs/overlayfs/params.c +++ b/fs/overlayfs/params.c @@ -282,13 +282,11 @@ static int ovl_mount_dir_check(struct fs_context *fc, const struct path *path, return invalfc(fc, "%s is not a directory", name); /* - * Root dentries of case-insensitive capable filesystems might - * not have the dentry operations set, but still be incompatible - * with overlayfs. Check explicitly to prevent post-mount - * failures. + * Allow filesystems that are case-folding capable but deny composing + * ovl stack from case-folded directories. */ - if (sb_has_encoding(path->mnt->mnt_sb)) - return invalfc(fc, "case-insensitive capable filesystem on %s not supported", name); + if (ovl_dentry_casefolded(path->dentry)) + return invalfc(fc, "case-insensitive directory on %s not supported", name); if (ovl_dentry_weird(path->dentry)) return invalfc(fc, "filesystem on %s not supported", name); diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index dcccb4b4a66c..593c4da107d6 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -206,10 +206,17 @@ bool ovl_dentry_weird(struct dentry *dentry) if (!d_can_lookup(dentry) && !d_is_file(dentry) && !d_is_symlink(dentry)) return true; - return dentry->d_flags & (DCACHE_NEED_AUTOMOUNT | - DCACHE_MANAGE_TRANSIT | - DCACHE_OP_HASH | - DCACHE_OP_COMPARE); + if (dentry->d_flags & (DCACHE_NEED_AUTOMOUNT | DCACHE_MANAGE_TRANSIT)) + return true; + + /* + * Allow filesystems that are case-folding capable but deny composing + * ovl stack from case-folded directories. + */ + if (sb_has_encoding(dentry->d_sb)) + return IS_CASEFOLDED(d_inode(dentry)); + + return dentry->d_flags & (DCACHE_OP_HASH | DCACHE_OP_COMPARE); } enum ovl_path_type ovl_path_type(struct dentry *dentry) -- 2.34.1
