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-rw-r--r--fs/erofs/super.c18
1 files changed, 12 insertions, 6 deletions
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 937a215f626c..e93264034b5d 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -644,14 +644,20 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
* fs contexts (including its own) due to self-controlled RO
* accesses/contexts and no side-effect changes that need to
* context save & restore so it can reuse the current thread
- * context. However, it still needs to bump `s_stack_depth` to
- * avoid kernel stack overflow from nested filesystems.
+ * context.
+ * However, we still need to prevent kernel stack overflow due
+ * to filesystem nesting: just ensure that s_stack_depth is 0
+ * to disallow mounting EROFS on stacked filesystems.
+ * Note: s_stack_depth is not incremented here for now, since
+ * EROFS is the only fs supporting file-backed mounts for now.
+ * It MUST change if another fs plans to support them, which
+ * may also require adjusting FILESYSTEM_MAX_STACK_DEPTH.
*/
if (erofs_is_fileio_mode(sbi)) {
- sb->s_stack_depth =
- file_inode(sbi->dif0.file)->i_sb->s_stack_depth + 1;
- if (sb->s_stack_depth > FILESYSTEM_MAX_STACK_DEPTH) {
- erofs_err(sb, "maximum fs stacking depth exceeded");
+ inode = file_inode(sbi->dif0.file);
+ if ((inode->i_sb->s_op == &erofs_sops && !sb->s_bdev) ||
+ inode->i_sb->s_stack_depth) {
+ erofs_err(sb, "file-backed mounts cannot be applied to stacked fses");
return -ENOTBLK;
}
}