CVE-2021-46982

Summary

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

f2fs: compress: fix race condition of overwrite vs truncate

pos_fsstress testcase complains a panic as belew:

————[ cut here ]———— kernel BUG at fs/f2fs/compress.c:1082! invalid opcode: 0000 [#1] SMP PTI CPU: 4 PID: 2753477 Comm: kworker/u16:2 Tainted: G OE 5.12.0-rc1-custom #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014 Workqueue: writeback wb_workfn (flush-252:16) RIP: 0010:prepare_compress_overwrite+0x4c0/0x760 [f2fs] Call Trace: f2fs_prepare_compress_overwrite+0x5f/0x80 [f2fs] f2fs_write_cache_pages+0x468/0x8a0 [f2fs] f2fs_write_data_pages+0x2a4/0x2f0 [f2fs] do_writepages+0x38/0xc0 __writeback_single_inode+0x44/0x2a0 writeback_sb_inodes+0x223/0x4d0 __writeback_inodes_wb+0x56/0xf0 wb_writeback+0x1dd/0x290 wb_workfn+0x309/0x500 process_one_work+0x220/0x3c0 worker_thread+0x53/0x420 kthread+0x12f/0x150 ret_from_fork+0x22/0x30

The root cause is truncate() may race with overwrite as below, so that one reference count left in page can not guarantee the page attaching in mapping tree all the time, after truncation, later find_lock_page() may return NULL pointer.

  • prepare_compress_overwrite
  • f2fs_pagecache_get_page
  • unlock_page - f2fs_setattr - truncate_setsize - truncate_inode_page - delete_from_page_cache
  • find_lock_page

Fix this by avoiding referencing updated page.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux4c8ff7095bef64fc47e996a938f7d57f9e077da3 < 5639b73fd3bc6fc8ca72e3a9ac15aacaabd7ebffaffected
LinuxLinux4c8ff7095bef64fc47e996a938f7d57f9e077da3 < 64acb100fe3beb5d20184d0ae3307235bd3555c4affected
LinuxLinux4c8ff7095bef64fc47e996a938f7d57f9e077da3 < 936158b15e2648253afb824d252c910c496d34b5affected
LinuxLinux4c8ff7095bef64fc47e996a938f7d57f9e077da3 < a949dc5f2c5cfe0c910b664650f45371254c0744affected
LinuxLinux5.6affected
LinuxLinux0 < 5.6unaffected
LinuxLinux5.10.38 <= 5.10.*unaffected
LinuxLinux5.11.22 <= 5.11.*unaffected
LinuxLinux5.12.5 <= 5.12.*unaffected
LinuxLinux5.13 <= *unaffected

Weaknesses

ADP Enrichment

CVE Program Container

Additional References

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References