erofs: avoid using multiple devices with different type

For multiple devices, both primary and extra devices should be the
same type. `erofs_init_device` has already guaranteed that if the
primary is a file-backed device, extra devices should also be
regular files.

However, if the primary is a block device while the extra device
is a file-backed device, `erofs_init_device` will get an ENOTBLK,
which is not treated as an error in `erofs_fc_get_tree`, and that
leads to an UAF:

  erofs_fc_get_tree
    get_tree_bdev_flags(erofs_fc_fill_super)
      erofs_read_superblock
        erofs_init_device  // sbi->dif0 is not inited yet,
                           // return -ENOTBLK
      deactivate_locked_super
        free(sbi)
    if (err is -ENOTBLK)
      sbi->dif0.file = filp_open()  // sbi UAF

So if -ENOTBLK is hitted in `erofs_init_device`, it means the
primary device must be a block device, and the extra device
is not a block device. The error can be converted to -EINVAL.

Fixes: fb176750266a ("erofs: add file-backed mount support")
Signed-off-by: Sheng Yong <shengyong1@xiaomi.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Hongbo Li <lihongbo22@huawei.com>
Link: https://lore.kernel.org/r/20250515014837.3315886-1-shengyong1@xiaomi.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index bcb99c3c2594b387ce7dfe8368107af4c99f291a..6e57b9cc6ed2e09a1886d3803b64871c6619513f 100644 (file)
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -165,8 +165,11 @@ static int erofs_init_device(struct erofs_buf *buf, struct super_block *sb,
                                filp_open(dif->path, O_RDONLY | O_LARGEFILE, 0) :
                                bdev_file_open_by_path(dif->path,
                                                BLK_OPEN_READ, sb->s_type, NULL);
-               if (IS_ERR(file))
+               if (IS_ERR(file)) {
+                       if (file == ERR_PTR(-ENOTBLK))
+                               return -EINVAL;
                        return PTR_ERR(file);
+               }
 
                if (!erofs_is_fileio_mode(sbi)) {
                        dif->dax_dev = fs_dax_get_by_bdev(file_bdev(file),