CVE-2025-71065

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

f2fs: fix to avoid potential deadlock

As Jiaming Zhang and syzbot reported, there is potential deadlock in f2fs as below:

Chain exists of: &sbi->cp_rwsem –> fs_reclaim –> sb_internal#2

Possible unsafe locking scenario:

   CPU0                    CPU1
   ----                    ----

rlock(sb_internal#2); lock(fs_reclaim); lock(sb_internal#2); rlock(&sbi->cp_rwsem);

*** DEADLOCK ***

3 locks held by kswapd0/73: #0: ffffffff8e247a40 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:7015 [inline] #0: ffffffff8e247a40 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x951/0x2800 mm/vmscan.c:7389 #1: ffff8880118400e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_trylock_shared fs/super.c:562 [inline] #1: ffff8880118400e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_cache_scan+0x91/0x4b0 fs/super.c:197 #2: ffff888011840610 (sb_internal#2){.+.+}-{0:0}, at: f2fs_evict_inode+0x8d9/0x1b60 fs/f2fs/inode.c:890

stack backtrace: CPU: 0 UID: 0 PID: 73 Comm: kswapd0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175 check_prev_add kernel/locking/lockdep.c:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537 f2fs_down_read fs/f2fs/f2fs.h:2278 [inline] f2fs_lock_op fs/f2fs/f2fs.h:2357 [inline] f2fs_do_truncate_blocks+0x21c/0x10c0 fs/f2fs/file.c:791 f2fs_truncate_blocks+0x10a/0x300 fs/f2fs/file.c:867 f2fs_truncate+0x489/0x7c0 fs/f2fs/file.c:925 f2fs_evict_inode+0x9f2/0x1b60 fs/f2fs/inode.c:897 evict+0x504/0x9c0 fs/inode.c:810 f2fs_evict_inode+0x1dc/0x1b60 fs/f2fs/inode.c:853 evict+0x504/0x9c0 fs/inode.c:810 dispose_list fs/inode.c:852 [inline] prune_icache_sb+0x21b/0x2c0 fs/inode.c:1000 super_cache_scan+0x39b/0x4b0 fs/super.c:224 do_shrink_slab+0x6ef/0x1110 mm/shrinker.c:437 shrink_slab_memcg mm/shrinker.c:550 [inline] shrink_slab+0x7ef/0x10d0 mm/shrinker.c:628 shrink_one+0x28a/0x7c0 mm/vmscan.c:4955 shrink_many mm/vmscan.c:5016 [inline] lru_gen_shrink_node mm/vmscan.c:5094 [inline] shrink_node+0x315d/0x3780 mm/vmscan.c:6081 kswapd_shrink_node mm/vmscan.c:6941 [inline] balance_pgdat mm/vmscan.c:7124 [inline] kswapd+0x147c/0x2800 mm/vmscan.c:7389 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The root cause is deadlock among four locks as below:

kswapd

• fs_reclaim — Lock A

• shrink_one

• evict

• f2fs_evict_inode - sb_start_intwrite — Lock B

• iput

• evict

• f2fs_evict_inode

• sb_start_intwrite — Lock B

• f2fs_truncate - f2fs_truncate_blocks

  • f2fs_do_truncate_blocks
  • f2fs_lock_op — Lock C

ioctl

• f2fs_ioc_commit_atomic_write
• f2fs_lock_op — Lock C
• __f2fs_commit_atomic_write
• __replace_atomic_write_block - f2fs_get_dnode_of_data
  • __get_node_folio
  • f2fs_check_nid_range
  • f2fs_handle_error
  • f2fs_record_errors - f2fs_down_write — Lock D

open

• do_open
• do_truncate
• security_inode_need_killpriv
• f2fs_getxattr - lookup_all_xattrs
  • f2fs_handle_error
  • f2fs_record_errors
  • f2fs_down_write — Lock D
  • f2fs_commit_super - read_mapping_folio
    • filemap_alloc_folio_noprof
    • prepare_alloc_pages
    • fs_reclaim_acquire — Lock A

In order to a —truncated—

Affected Software

References

• https://git.kernel.org/stable/c/6c3bab5c6261aa22c561ef56b7365959a90e7d91
• https://git.kernel.org/stable/c/86a85a7b622e6e8dba69810257733ce5eab5ed55
• https://git.kernel.org/stable/c/8bd6dff8b801abaa362272894bda795bf0cf1307
• https://git.kernel.org/stable/c/ca8b201f28547e28343a6f00a6e91fa8c09572fe