CVE-2025-22123 Information

Apr 17, 2025 cve

Description

In the Linux kernel the following vulnerability has been resolved:

f2fs: fix to avoid accessing uninitialized curseg

syzbot reports a f2fs bug as below:

F2FS-fs (loop3): Stopped filesystem due to reason: 7 kworker/u8:7: attempt to access beyond end of device BUG: unable to handle page fault for address: ffffed1604ea3dfa RIP: 0010:get_ckpt_valid_blocks fs/f2fs/segment.h:361 [inline] RIP: 0010:has_curseg_enough_space fs/f2fs/segment.h:570 [inline] RIP: 0010:__get_secs_required fs/f2fs/segment.h:620 [inline] RIP: 0010:has_not_enough_free_secs fs/f2fs/segment.h:633 [inline] RIP: 0010:has_enough_free_secs+0x575/0x1660 fs/f2fs/segment.h:649 f2fs_is_checkpoint_ready fs/f2fs/segment.h:671 [inline] f2fs_write_inode+0x425/0x540 fs/f2fs/inode.c:791 write_inode fs/fs-writeback.c:1525 [inline] __writeback_single_inode+0x708/0x10d0 fs/fs-writeback.c:1745 writeback_sb_inodes+0x820/0x1360 fs/fs-writeback.c:1976 wb_writeback+0x413/0xb80 fs/fs-writeback.c:2156 wb_do_writeback fs/fs-writeback.c:2303 [inline] wb_workfn+0x410/0x1080 fs/fs-writeback.c:2343 process_one_work kernel/workqueue.c:3236 [inline] process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317 worker_thread+0x870/0xd30 kernel/workqueue.c:3398 kthread+0x7a9/0x920 kernel/kthread.c:464 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Commit 8b10d3653735 ( 2fs: introduce FAULT_NO_SEGMENT) allows to trigger no free segment fault in allocator then it will update curseg->segno to NULL_SEGNO though CP_ERROR_FLAG has been set f2fs_write_inode() missed to check the flag and access invalid curseg->segno directly in below call path then resulting in panic:

  • f2fs_write_inode
  • f2fs_is_checkpoint_ready
  • has_enough_free_secs
  • has_not_enough_free_secs - __get_secs_required
    • has_curseg_enough_space
    • get_ckpt_valid_blocks : access invalid curseg->segno

To avoid this issue let’s:

  • check CP_ERROR_FLAG flag in prior to f2fs_is_checkpoint_ready() in f2fs_write_inode().
  • in has_curseg_enough_space() save curseg->segno into a temp variable and verify its validation before use.

Reference

https://git.kernel.org/stable/c/7f90e5d423cd2d4c74b2abb527872f335108637f https://git.kernel.org/stable/c/986c50f6bca109c6cf362b4e2babcb85aba958f6

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