CVE-2024-44941

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

f2fs: fix to cover read extent cache access with lock

syzbot reports a f2fs bug as below:

BUG: KASAN: slab-use-after-free in sanitycheckextentcache+0x370/0x410 fs/f2fs/extentcache.c:46 Read of size 4 at addr ffff8880739ab220 by task syz-executor200/5097

CPU: 0 PID: 5097 Comm: syz-executor200 Not tainted 6.9.0-rc6-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024 Call Trace: <TASK> _dumpstack lib/dumpstack.c:88 [inline] dumpstacklvl+0x241/0x360 lib/dumpstack.c:114 printaddressdescription mm/kasan/report.c:377 [inline] printreport+0x169/0x550 mm/kasan/report.c:488 kasanreport+0x143/0x180 mm/kasan/report.c:601 sanitycheckextentcache+0x370/0x410 fs/f2fs/extentcache.c:46 doreadinode fs/f2fs/inode.c:509 [inline] f2fsiget+0x33e1/0x46e0 fs/f2fs/inode.c:560 f2fsnfsgetinode+0x74/0x100 fs/f2fs/super.c:3237 genericfhtodentry+0x9f/0xf0 fs/libfs.c:1413 exportfsdecodefhraw+0x152/0x5f0 fs/exportfs/expfs.c:444 exportfsdecodefh+0x3c/0x80 fs/exportfs/expfs.c:584 dohandletopath fs/fhandle.c:155 [inline] handletopath fs/fhandle.c:210 [inline] dohandleopen+0x495/0x650 fs/fhandle.c:226 dosyscallx64 arch/x86/entry/common.c:52 [inline] dosyscall64+0xf5/0x240 arch/x86/entry/common.c:83 entrySYSCALL64after_hwframe+0x77/0x7f

We missed to cover sanitycheckextent_cache() w/ extent cache lock, so, below race case may happen, result in use after free issue.

• f2fsiget
  • doreadinode
    • f2fsinitreadextenttree : add largest extent entry in to cache
      • shrink
        • f2fsshrinkreadextenttree
          • shrinkextenttree
            • detachextentnode : drop largest extent entry
    • sanitycheckextentcache : access et->largest w/o lock

let's refactor sanitycheckextentcache() to avoid extent cache access and call it before f2fsinitreadextent_tree() to fix this issue.