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Message-ID: <2024022823-CVE-2021-46982-5134@gregkh> Date: Wed, 28 Feb 2024 09:14:32 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: gregkh@...nel.org Subject: CVE-2021-46982: f2fs: compress: fix race condition of overwrite vs truncate From: gregkh@...nel.org 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 4c8ff7095bef and fixed in 5.10.38 with commit 5639b73fd3bc Issue introduced in 5.6 with commit 4c8ff7095bef and fixed in 5.11.22 with commit 64acb100fe3b Issue introduced in 5.6 with commit 4c8ff7095bef and fixed in 5.12.5 with commit 936158b15e26 Issue introduced in 5.6 with commit 4c8ff7095bef and fixed in 5.13 with commit a949dc5f2c5c Please see https://www.kernel.org or 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
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