CVE-2025-38172 — erofs: avoid using multiple devices with different type

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

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.

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CVE-2025-38172 — erofs: avoid using multiple devices with different type