Linux Kernel up to 5.12.6 btrfs permission

Summaryinfo

A vulnerability was found in Linux Kernel up to 5.12.6. It has been declared as critical. This affects an unknown function of the component btrfs. The manipulation results in permission. This vulnerability is known as CVE-2021-47072. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as critical, was found in Linux Kernel up to 5.12.6 (Operating System). Affected is some unknown processing of the component btrfs. The manipulation with an unknown input leads to a permission vulnerability. CWE is classifying the issue as CWE-275. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix removed dentries still existing after log is synced When we move one inode from one directory to another and both the inode and its previous parent directory were logged before, we are not supposed to have the dentry for the old parent if we have a power failure after the log is synced. Only the new dentry is supposed to exist. Generally this works correctly, however there is a scenario where this is not currently working, because the old parent of the file/directory that was moved is not authoritative for a range that includes the dir index and dir item keys of the old dentry. This case is better explained with the following example and reproducer: # The test requires a very specific layout of keys and items in the # fs/subvolume btree to trigger the bug. So we want to make sure that # on whatever platform we are, we have the same leaf/node size. # # Currently in btrfs the node/leaf size can not be smaller than the page # size (but it can be greater than the page size). So use the largest # supported node/leaf size (64K). $ mkfs.btrfs -f -n 65536 /dev/sdc $ mount /dev/sdc /mnt # "testdir" is inode 257. $ mkdir /mnt/testdir $ chmod 755 /mnt/testdir # Create several empty files to have the directory "testdir" with its # items spread over several leaves (7 in this case). $ for ((i = 1; i <= 1200; i++)); do echo -n > /mnt/testdir/file$i done # Create our test directory "dira", inode number 1458, which gets all # its items in leaf 7. # # The BTRFS_DIR_ITEM_KEY item for inode 257 ("testdir") that points to # the entry named "dira" is in leaf 2, while the BTRFS_DIR_INDEX_KEY # item that points to that entry is in leaf 3. # # For this particular filesystem node size (64K), file count and file # names, we endup with the directory entry items from inode 257 in # leaves 2 and 3, as previously mentioned - what matters for triggering # the bug exercised by this test case is that those items are not placed # in leaf 1, they must be placed in a leaf different from the one # containing the inode item for inode 257. # # The corresponding BTRFS_DIR_ITEM_KEY and BTRFS_DIR_INDEX_KEY items for # the parent inode (257) are the following: # # item 460 key (257 DIR_ITEM 3724298081) itemoff 48344 itemsize 34 # location key (1458 INODE_ITEM 0) type DIR # transid 6 data_len 0 name_len 4 # name: dira # # and: # # item 771 key (257 DIR_INDEX 1202) itemoff 36673 itemsize 34 # location key (1458 INODE_ITEM 0) type DIR # transid 6 data_len 0 name_len 4 # name: dira $ mkdir /mnt/testdir/dira # Make sure everything done so far is durably persisted. $ sync # Now do a change to inode 257 ("testdir") that does not result in # COWing leaves 2 and 3 - the leaves that contain the directory items # pointing to inode 1458 (directory "dira"). # # Changing permissions, the owner/group, updating or adding a xattr, # etc, will not change (COW) leaves 2 and 3. So for the sake of # simplicity change the permissions of inode 257, which results in # updating its inode item and therefore change (COW) only leaf 1. $ chmod 700 /mnt/testdir # Now fsync directory inode 257. # # Since only the first leaf was changed/COWed, we log the inode item of # inode 257 and only the dentries found in the first leaf, all have a # key type of BTRFS_DIR_ITEM_KEY, and no keys of type # BTRFS_DIR_INDEX_KEY, because they sort after the former type and none # exist in the first leaf. # # We also log 3 items that represent ranges for dir items and dir # indexes for which the log is authoritative: # # 1) a key of type BTRFS_DIR_LOG_ITEM_KEY, which indicates the log is # authoritative for all BTRFS_DIR_ITEM_KEY keys that have an offset # in the range [0, 2285968570] (the offset here is th ---truncated---

The weakness was published 03/02/2024. The advisory is available at git.kernel.org. This vulnerability is traded as CVE-2021-47072 since 02/29/2024. The technical details are unknown and an exploit is not available. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 01/09/2025). This vulnerability is assigned to T1222 by the MITRE ATT&CK project.

Upgrading to version 5.12.7 or 5.13 eliminates this vulnerability. Applying the patch 6d0924c5b742/54a40fc3a1da is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 5.12.0
• 5.12.1
• 5.12.2
• 5.12.3
• 5.12.4
• 5.12.5
• 5.12.6

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

• 🔍
• 🔍
• 🔍

CPE 2.2info

• 🔍
• 🔍
• 🔍

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Discussion