| From bippy-1.1.0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@kernel.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2022-49850: nilfs2: fix deadlock in nilfs_count_free_blocks() |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| nilfs2: fix deadlock in nilfs_count_free_blocks() |
| |
| A semaphore deadlock can occur if nilfs_get_block() detects metadata |
| corruption while locating data blocks and a superblock writeback occurs at |
| the same time: |
| |
| task 1 task 2 |
| ------ ------ |
| * A file operation * |
| nilfs_truncate() |
| nilfs_get_block() |
| down_read(rwsem A) <-- |
| nilfs_bmap_lookup_contig() |
| ... generic_shutdown_super() |
| nilfs_put_super() |
| * Prepare to write superblock * |
| down_write(rwsem B) <-- |
| nilfs_cleanup_super() |
| * Detect b-tree corruption * nilfs_set_log_cursor() |
| nilfs_bmap_convert_error() nilfs_count_free_blocks() |
| __nilfs_error() down_read(rwsem A) <-- |
| nilfs_set_error() |
| down_write(rwsem B) <-- |
| |
| *** DEADLOCK *** |
| |
| Here, nilfs_get_block() readlocks rwsem A (= NILFS_MDT(dat_inode)->mi_sem) |
| and then calls nilfs_bmap_lookup_contig(), but if it fails due to metadata |
| corruption, __nilfs_error() is called from nilfs_bmap_convert_error() |
| inside the lock section. |
| |
| Since __nilfs_error() calls nilfs_set_error() unless the filesystem is |
| read-only and nilfs_set_error() attempts to writelock rwsem B (= |
| nilfs->ns_sem) to write back superblock exclusively, hierarchical lock |
| acquisition occurs in the order rwsem A -> rwsem B. |
| |
| Now, if another task starts updating the superblock, it may writelock |
| rwsem B during the lock sequence above, and can deadlock trying to |
| readlock rwsem A in nilfs_count_free_blocks(). |
| |
| However, there is actually no need to take rwsem A in |
| nilfs_count_free_blocks() because it, within the lock section, only reads |
| a single integer data on a shared struct with |
| nilfs_sufile_get_ncleansegs(). This has been the case after commit |
| aa474a220180 ("nilfs2: add local variable to cache the number of clean |
| segments"), that is, even before this bug was introduced. |
| |
| So, this resolves the deadlock problem by just not taking the semaphore in |
| nilfs_count_free_blocks(). |
| |
| The Linux kernel CVE team has assigned CVE-2022-49850 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 4.9.334 with commit 3c89ca6d3dfa6c09c515807a7a97a521f5d5147e |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 4.14.300 with commit 8b4506cff6630bb474bb46a2a75c31e533a756ba |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 4.19.267 with commit f0cc93080d4c09510b74ecba87fd778cca390bb1 |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 5.4.225 with commit 36ff974b0310771417c0be64b64aa221bd70d63d |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 5.10.155 with commit 1d4ff73062096c21b47954d2996b4df259777bda |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 5.15.79 with commit abc082aac0d9b6b926038fc3adb7008306581be2 |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 6.0.9 with commit cb029b54953420f7a2d65100f1c5107f14411bdc |
| Issue introduced in 2.6.38 with commit e828949e5b42bfd234ee537cdb7c5e3a577958a3 and fixed in 6.1 with commit 8ac932a4921a96ca52f61935dbba64ea87bbd5dc |
| |
| 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-2022-49850 |
| 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/nilfs2/the_nilfs.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/3c89ca6d3dfa6c09c515807a7a97a521f5d5147e |
| https://git.kernel.org/stable/c/8b4506cff6630bb474bb46a2a75c31e533a756ba |
| https://git.kernel.org/stable/c/f0cc93080d4c09510b74ecba87fd778cca390bb1 |
| https://git.kernel.org/stable/c/36ff974b0310771417c0be64b64aa221bd70d63d |
| https://git.kernel.org/stable/c/1d4ff73062096c21b47954d2996b4df259777bda |
| https://git.kernel.org/stable/c/abc082aac0d9b6b926038fc3adb7008306581be2 |
| https://git.kernel.org/stable/c/cb029b54953420f7a2d65100f1c5107f14411bdc |
| https://git.kernel.org/stable/c/8ac932a4921a96ca52f61935dbba64ea87bbd5dc |
