diff options
| -rw-r--r-- | fs/erofs/super.c | 18 |
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; } } |