| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2021-46982: f2fs: compress: fix race condition of overwrite vs truncate |
| |
| Description |
| =========== |
| |
| 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. |
| |
| The Linux kernel CVE team has assigned CVE-2021-46982 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.6 with commit 4c8ff7095bef64fc47e996a938f7d57f9e077da3 and fixed in 5.10.38 with commit 5639b73fd3bc6fc8ca72e3a9ac15aacaabd7ebff |
| Issue introduced in 5.6 with commit 4c8ff7095bef64fc47e996a938f7d57f9e077da3 and fixed in 5.11.22 with commit 64acb100fe3beb5d20184d0ae3307235bd3555c4 |
| Issue introduced in 5.6 with commit 4c8ff7095bef64fc47e996a938f7d57f9e077da3 and fixed in 5.12.5 with commit 936158b15e2648253afb824d252c910c496d34b5 |
| Issue introduced in 5.6 with commit 4c8ff7095bef64fc47e996a938f7d57f9e077da3 and fixed in 5.13 with commit a949dc5f2c5cfe0c910b664650f45371254c0744 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2021-46982 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| fs/f2fs/compress.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/5639b73fd3bc6fc8ca72e3a9ac15aacaabd7ebff |
| https://git.kernel.org/stable/c/64acb100fe3beb5d20184d0ae3307235bd3555c4 |
| https://git.kernel.org/stable/c/936158b15e2648253afb824d252c910c496d34b5 |
| https://git.kernel.org/stable/c/a949dc5f2c5cfe0c910b664650f45371254c0744 |
