🛡️ CVE-2023-53183 — kernel

btrfs: exit gracefully if reloc roots don't match

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

btrfs: exit gracefully if reloc roots don't match

[BUG]

Syzbot reported a crash that an ASSERT() got triggered inside

prepare_to_merge().

[CAUSE]

The root cause of the triggered ASSERT() is we can have a race between

quota tree creation and relocation.

This leads us to create a duplicated quota tree in the

btrfs_read_fs_root() path, and since it's treated as fs tree, it would

have ROOT_SHAREABLE flag, causing us to create a reloc tree for it.

The bug itself is fixed by a dedicated patch for it, but this already

taught us the ASSERT() is not something straightforward for

developers.

[ENHANCEMENT]

Instead of using an ASSERT(), let's handle it gracefully and output

extra info about the mismatch reloc roots to help debug.

Also with the above ASSERT() removed, we can trigger ASSERT(0)s inside

merge_reloc_roots() later.

Also replace those ASSERT(0)s with WARN_ON()s.