CVE-2025-40150

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

f2fs: fix to avoid migrating empty section

It reports a bug from device w/ zufs:

F2FS-fs (dm-64): Inconsistent segment (173822) type [1, 0] in SSA and SIT F2FS-fs (dm-64): Stopped filesystem due to reason: 4

Thread A Thread B

• f2fs_expand_inode_data
• f2fs_allocate_pinning_section
• f2fs_gc_range
• do_garbage_collect w/ segno #x - writepage - f2fs_allocate_data_block - new_curseg - allocate segno #x

The root cause is: fallocate on pinning file may race w/ block allocation as above, result in do_garbage_collect() from fallocate() may migrate segment which is just allocated by a log, the log will update segment type in its in-memory structure, however GC will get segment type from on-disk SSA block, once segment type changes by log, we can detect such inconsistency, then shutdown filesystem.

In this case, on-disk SSA shows type of segno #173822 is 1 (SUM_TYPE_NODE), however segno #173822 was just allocated as data type segment, so in-memory SIT shows type of segno #173822 is 0 (SUM_TYPE_DATA).

Change as below to fix this issue:

• check whether current section is empty before gc
• add sanity checks on do_garbage_collect() to avoid any race case, result in migrating segment used by log.
• btw, it fixes misc issue in printed logs: SSA and SIT -> SIT and SSA.

References

• https://git.kernel.org/stable/c/d625a2b08c089397d3a03bff13fa8645e4ec7a01
• https://git.kernel.org/stable/c/eec1589be36fcf7440755703e4faeee2c01e360b