Amir Goldstein <amir73il@xxxxxxxxx> writes:
> On Mon, Aug 25, 2025 at 5:27 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>>
>> On Mon, Aug 25, 2025 at 1:09 PM Gabriel Krisman Bertazi
>> <gabriel@xxxxxxxxxx> wrote:
>> >
>> > André Almeida <andrealmeid@xxxxxxxxxx> writes:
>> >
>> > > To add overlayfs support casefold layers, create a new function
>> > > ovl_casefold(), to be able to do case-insensitive strncmp().
>> > >
>> > > ovl_casefold() allocates a new buffer and stores the casefolded version
>> > > of the string on it. If the allocation or the casefold operation fails,
>> > > fallback to use the original string.
>> > >
>> > > The case-insentive name is then used in the rb-tree search/insertion
>> > > operation. If the name is found in the rb-tree, the name can be
>> > > discarded and the buffer is freed. If the name isn't found, it's then
>> > > stored at struct ovl_cache_entry to be used later.
>> > >
>> > > Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
>> > > Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
>> > > ---
>> > > Changes from v6:
>> > > - Last version was using `strncmp(... tmp->len)` which was causing
>> > > regressions. It should be `strncmp(... len)`.
>> > > - Rename cf_len to c_len
>> > > - Use c_len for tree operation: (cmp < 0 || len < tmp->c_len)
>> > > - Remove needless kfree(cf_name)
>> > > ---
>> > > fs/overlayfs/readdir.c | 113 ++++++++++++++++++++++++++++++++++++++++---------
>> > > 1 file changed, 94 insertions(+), 19 deletions(-)
>> > >
>> > > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
>> > > index b65cdfce31ce27172d28d879559f1008b9c87320..dfc661b7bc3f87efbf14991e97cee169400d823b 100644
>> > > --- a/fs/overlayfs/readdir.c
>> > > +++ b/fs/overlayfs/readdir.c
>> > > @@ -27,6 +27,8 @@ struct ovl_cache_entry {
>> > > bool is_upper;
>> > > bool is_whiteout;
>> > > bool check_xwhiteout;
>> > > + const char *c_name;
>> > > + int c_len;
>> > > char name[];
>> > > };
>> > >
>> > > @@ -45,6 +47,7 @@ struct ovl_readdir_data {
>> > > struct list_head *list;
>> > > struct list_head middle;
>> > > struct ovl_cache_entry *first_maybe_whiteout;
>> > > + struct unicode_map *map;
>> > > int count;
>> > > int err;
>> > > bool is_upper;
>> > > @@ -66,6 +69,27 @@ static struct ovl_cache_entry *ovl_cache_entry_from_node(struct rb_node *n)
>> > > return rb_entry(n, struct ovl_cache_entry, node);
>> > > }
>> > >
>> > > +static int ovl_casefold(struct unicode_map *map, const char *str, int len, char **dst)
>> > > +{
>> > > + const struct qstr qstr = { .name = str, .len = len };
>> > > + int cf_len;
>> > > +
>> > > + if (!IS_ENABLED(CONFIG_UNICODE) || !map || is_dot_dotdot(str, len))
>> > > + return 0;
>> > > +
>> > > + *dst = kmalloc(NAME_MAX, GFP_KERNEL);
>> > > +
>> > > + if (dst) {
>> > > + cf_len = utf8_casefold(map, &qstr, *dst, NAME_MAX);
>> > > +
>> > > + if (cf_len > 0)
>> > > + return cf_len;
>> > > + }
>> > > +
>> > > + kfree(*dst);
>> > > + return 0;
>> > > +}
>> >
>> > Hi,
>> >
>> > I should just note this does not differentiates allocation errors from
>> > casefolding errors (invalid encoding). It might be just a theoretical
>> > error because GFP_KERNEL shouldn't fail (wink, wink) and the rest of the
>> > operation is likely to fail too, but if you have an allocation failure, you
>> > can end up with an inconsistent cache, because a file is added under the
>> > !casefolded name and a later successful lookup will look for the
>> > casefolded version.
>>
>> Good point.
>> I will fix this in my tree.
>
> wait why should we not fail to fill the cache for both allocation
> and encoding errors?
>
We shouldn't fail the cache for encoding errors, just for allocation errors.
Perhaps I am misreading the code, so please correct me if I'm wrong. if
ovl_casefold fails, the non-casefolded name is used in the cache. That
makes sense if the reason utf8_casefold failed is because the string
cannot be casefolded (i.e. an invalid utf-8 string). For those strings,
everything is fine. But on an allocation failure, the string might have
a real casefolded version. If we fallback to the original string as the
key, a cache lookup won't find the entry, since we compare with memcmp.
>
>>
>> >
>> > > +
>> > > static bool ovl_cache_entry_find_link(const char *name, int len,
>> > > struct rb_node ***link,
>> > > struct rb_node **parent)
>> > > @@ -79,10 +103,10 @@ static bool ovl_cache_entry_find_link(const char *name, int len,
>> > >
>> > > *parent = *newp;
>> > > tmp = ovl_cache_entry_from_node(*newp);
>> > > - cmp = strncmp(name, tmp->name, len);
>> > > + cmp = strncmp(name, tmp->c_name, len);
>> > > if (cmp > 0)
>> > > newp = &tmp->node.rb_right;
>> > > - else if (cmp < 0 || len < tmp->len)
>> > > + else if (cmp < 0 || len < tmp->c_len)
>> > > newp = &tmp->node.rb_left;
>> > > else
>> > > found = true;
>> > > @@ -101,10 +125,10 @@ static struct ovl_cache_entry *ovl_cache_entry_find(struct rb_root *root,
>> > > while (node) {
>> > > struct ovl_cache_entry *p = ovl_cache_entry_from_node(node);
>> > >
>> > > - cmp = strncmp(name, p->name, len);
>> > > + cmp = strncmp(name, p->c_name, len);
>> > > if (cmp > 0)
>> > > node = p->node.rb_right;
>> > > - else if (cmp < 0 || len < p->len)
>> > > + else if (cmp < 0 || len < p->c_len)
>> > > node = p->node.rb_left;
>> > > else
>> > > return p;
>> > > @@ -145,6 +169,7 @@ static bool ovl_calc_d_ino(struct ovl_readdir_data *rdd,
>> > >
>> > > static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
>> > > const char *name, int len,
>> > > + const char *c_name, int c_len,
>> > > u64 ino, unsigned int d_type)
>> > > {
>> > > struct ovl_cache_entry *p;
>> > > @@ -167,6 +192,14 @@ static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
>> > > /* Defer check for overlay.whiteout to ovl_iterate() */
>> > > p->check_xwhiteout = rdd->in_xwhiteouts_dir && d_type == DT_REG;
>> > >
>> > > + if (c_name && c_name != name) {
>> > > + p->c_name = c_name;
>> > > + p->c_len = c_len;
>> > > + } else {
>> > > + p->c_name = p->name;
>> > > + p->c_len = len;
>> > > + }
>> > > +
>> > > if (d_type == DT_CHR) {
>> > > p->next_maybe_whiteout = rdd->first_maybe_whiteout;
>> > > rdd->first_maybe_whiteout = p;
>> > > @@ -174,48 +207,55 @@ static struct ovl_cache_entry *ovl_cache_entry_new(struct ovl_readdir_data *rdd,
>> > > return p;
>> > > }
>> > >
>> > > -static bool ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
>> > > - const char *name, int len, u64 ino,
>> > > +/* Return 0 for found, 1 for added, <0 for error */
>> > > +static int ovl_cache_entry_add_rb(struct ovl_readdir_data *rdd,
>> > > + const char *name, int len,
>> > > + const char *c_name, int c_len,
>> > > + u64 ino,
>> > > unsigned int d_type)
>> > > {
>> > > struct rb_node **newp = &rdd->root->rb_node;
>> > > struct rb_node *parent = NULL;
>> > > struct ovl_cache_entry *p;
>> > >
>> > > - if (ovl_cache_entry_find_link(name, len, &newp, &parent))
>> > > - return true;
>> > > + if (ovl_cache_entry_find_link(c_name, c_len, &newp, &parent))
>> > > + return 0;
>> > >
>> > > - p = ovl_cache_entry_new(rdd, name, len, ino, d_type);
>> > > + p = ovl_cache_entry_new(rdd, name, len, c_name, c_len, ino, d_type);
>> > > if (p == NULL) {
>> > > rdd->err = -ENOMEM;
>> > > - return false;
>> > > + return -ENOMEM;
>> > > }
>> > >
>> > > list_add_tail(&p->l_node, rdd->list);
>> > > rb_link_node(&p->node, parent, newp);
>> > > rb_insert_color(&p->node, rdd->root);
>> > >
>> > > - return true;
>> > > + return 1;
>> > > }
>> > >
>> > > -static bool ovl_fill_lowest(struct ovl_readdir_data *rdd,
>> > > +/* Return 0 for found, 1 for added, <0 for error */
>> > > +static int ovl_fill_lowest(struct ovl_readdir_data *rdd,
>> > > const char *name, int namelen,
>> > > + const char *c_name, int c_len,
>> > > loff_t offset, u64 ino, unsigned int d_type)
>> > > {
>> > > struct ovl_cache_entry *p;
>> > >
>> > > - p = ovl_cache_entry_find(rdd->root, name, namelen);
>> > > + p = ovl_cache_entry_find(rdd->root, c_name, c_len);
>> > > if (p) {
>> > > list_move_tail(&p->l_node, &rdd->middle);
>> > > + return 0;
>> > > } else {
>> > > - p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
>> > > + p = ovl_cache_entry_new(rdd, name, namelen, c_name, c_len,
>> > > + ino, d_type);
>> > > if (p == NULL)
>> > > rdd->err = -ENOMEM;
>> > > else
>> > > list_add_tail(&p->l_node, &rdd->middle);
>> > > }
>> > >
>> > > - return rdd->err == 0;
>> > > + return rdd->err ?: 1;
>> > > }
>> > >
>> > > void ovl_cache_free(struct list_head *list)
>> > > @@ -223,8 +263,11 @@ void ovl_cache_free(struct list_head *list)
>> > > struct ovl_cache_entry *p;
>> > > struct ovl_cache_entry *n;
>> > >
>> > > - list_for_each_entry_safe(p, n, list, l_node)
>> > > + list_for_each_entry_safe(p, n, list, l_node) {
>> > > + if (p->c_name != p->name)
>> > > + kfree(p->c_name);
>> > > kfree(p);
>> > > + }
>> > >
>> > > INIT_LIST_HEAD(list);
>> > > }
>> > > @@ -260,12 +303,36 @@ static bool ovl_fill_merge(struct dir_context *ctx, const char *name,
>> > > {
>> > > struct ovl_readdir_data *rdd =
>> > > container_of(ctx, struct ovl_readdir_data, ctx);
>> > > + struct ovl_fs *ofs = OVL_FS(rdd->dentry->d_sb);
>> > > + const char *c_name = NULL;
>> > > + char *cf_name = NULL;
>> > > + int c_len = 0, ret;
>> > > +
>> > > + if (ofs->casefold)
>> > > + c_len = ovl_casefold(rdd->map, name, namelen, &cf_name);
>> > > +
>> > > + if (c_len <= 0) {
>> > > + c_name = name;
>> > > + c_len = namelen;
>> > > + } else {
>> > > + c_name = cf_name;
>> > > + }
>> > >
>> > > rdd->count++;
>> > > if (!rdd->is_lowest)
>> > > - return ovl_cache_entry_add_rb(rdd, name, namelen, ino, d_type);
>> > > + ret = ovl_cache_entry_add_rb(rdd, name, namelen, c_name, c_len, ino, d_type);
>> > > else
>> > > - return ovl_fill_lowest(rdd, name, namelen, offset, ino, d_type);
>> > > + ret = ovl_fill_lowest(rdd, name, namelen, c_name, c_len, offset, ino, d_type);
>> > > +
>> > > + /*
>> > > + * If ret == 1, that means that c_name is being used as part of struct
>> > > + * ovl_cache_entry and will be freed at ovl_cache_free(). Otherwise,
>> > > + * c_name was found in the rb-tree so we can free it here.
>> > > + */
>> > > + if (ret != 1 && c_name != name)
>> > > + kfree(c_name);
>> > > +
>> >
>> > The semantics of this being conditionally freed is a bit annoying, as
>> > it is already replicated in 3 places. I suppose a helper would come in
>> > hand.
>>
>> Yeh.
>>
>> I have already used ovl_cache_entry_free() in my tree.
>>
>> Thanks,
>> Amir.
>>
>> >
>> > In this specific case, it could just be:
>> >
>> > if (ret != 1)
>> > kfree(cf_name);
>> >
>> >
>> > > + return ret >= 0;
>> > > }
>> > >
>> > > static int ovl_check_whiteouts(const struct path *path, struct ovl_readdir_data *rdd)
>> > > @@ -357,12 +424,18 @@ static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list,
>> > > .list = list,
>> > > .root = root,
>> > > .is_lowest = false,
>> > > + .map = NULL,
>> > > };
>> > > int idx, next;
>> > > const struct ovl_layer *layer;
>> > > + struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
>> > >
>> > > for (idx = 0; idx != -1; idx = next) {
>> > > next = ovl_path_next(idx, dentry, &realpath, &layer);
>> > > +
>> > > + if (ofs->casefold)
>> > > + rdd.map = sb_encoding(realpath.dentry->d_sb);
>> > > +
>> > > rdd.is_upper = ovl_dentry_upper(dentry) == realpath.dentry;
>> > > rdd.in_xwhiteouts_dir = layer->has_xwhiteouts &&
>> > > ovl_dentry_has_xwhiteouts(dentry);
>> > > @@ -555,7 +628,7 @@ static bool ovl_fill_plain(struct dir_context *ctx, const char *name,
>> > > container_of(ctx, struct ovl_readdir_data, ctx);
>> > >
>> > > rdd->count++;
>> > > - p = ovl_cache_entry_new(rdd, name, namelen, ino, d_type);
>> > > + p = ovl_cache_entry_new(rdd, name, namelen, NULL, 0, ino, d_type);
>> > > if (p == NULL) {
>> > > rdd->err = -ENOMEM;
>> > > return false;
>> > > @@ -1023,6 +1096,8 @@ int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list)
>> > >
>> > > del_entry:
>> > > list_del(&p->l_node);
>> > > + if (p->c_name != p->name)
>> > > + kfree(p->c_name);
>> > > kfree(p);
>> > > }
>> >
>> > --
>> > Gabriel Krisman Bertazi
--
Gabriel Krisman Bertazi
