CVE-2025-22123

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:getckptvalidblocks fs/f2fs/segment.h:361 [inline] RIP: 0010:hascursegenoughspace fs/f2fs/segment.h:570 [inline] RIP: 0010:_getsecsrequired fs/f2fs/segment.h:620 [inline] RIP: 0010:hasnotenoughfreesecs fs/f2fs/segment.h:633 [inline] RIP: 0010:hasenoughfreesecs+0x575/0x1660 fs/f2fs/segment.h:649 <TASK> f2fsischeckpointready fs/f2fs/segment.h:671 [inline] f2fswriteinode+0x425/0x540 fs/f2fs/inode.c:791 writeinode fs/fs-writeback.c:1525 [inline] _writebacksingleinode+0x708/0x10d0 fs/fs-writeback.c:1745 writebacksbinodes+0x820/0x1360 fs/fs-writeback.c:1976 wbwriteback+0x413/0xb80 fs/fs-writeback.c:2156 wbdowriteback fs/fs-writeback.c:2303 [inline] wbworkfn+0x410/0x1080 fs/fs-writeback.c:2343 processonework kernel/workqueue.c:3236 [inline] processscheduledworks+0xa66/0x1840 kernel/workqueue.c:3317 workerthread+0x870/0xd30 kernel/workqueue.c:3398 kthread+0x7a9/0x920 kernel/kthread.c:464 retfromfork+0x4b/0x80 arch/x86/kernel/process.c:148 retfromforkasm+0x1a/0x30 arch/x86/entry/entry64.S:244

Commit 8b10d3653735 ("f2fs: introduce FAULTNOSEGMENT") allows to trigger no free segment fault in allocator, then it will update curseg->segno to NULLSEGNO, though, CPERRORFLAG has been set, f2fswrite_inode() missed to check the flag, and access invalid curseg->segno directly in below call path, then resulting in panic:

• f2fswriteinode
  • f2fsischeckpointready
    • hasenoughfreesecs
      • hasnotenoughfreesecs
        • getsecsrequired
          • hascursegenoughspace
            • getckptvalidblocks : access invalid curseg->segno

To avoid this issue, let's: - check CPERRORFLAG flag in prior to f2fsischeckpointready() in f2fswriteinode(). - in hascursegenoughspace(), save curseg->segno into a temp variable, and verify its validation before use.