CVE-2024-56581: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2024-56581

In the Linux kernel, the following vulnerability has been resolved: btrfs: ref-verify: fix use-after-free after invalid ref action At btrfs_ref_tree_mod() after we successfully inserted the new ref entry (local variable 'ref') into the respective block entry's rbtree (local variable 'be'), if we find an unexpected action of BTRFS_DROP_DELAYED_REF, we error out and free the ref entry without removing it from the block entry's rbtree. Then in the error path of btrfs_ref_tree_mod() we call btrfs_free_ref_cache(), which iterates over all block entries and then calls free_block_entry() for each one, and there we will trigger a use-after-free when we are called against the block entry to which we added the freed ref entry to its rbtree, since the rbtree still points to the block entry, as we didn't remove it from the rbtree before freeing it in the error path at btrfs_ref_tree_mod(). Fix this by removing the new ref entry from the rbtree before freeing it. Syzbot report this with the following stack traces: BTRFS error (device loop0 state EA): Ref action 2, root 5, ref_root 0, parent 8564736, owner 0, offset 0, num_refs 18446744073709551615 __btrfs_mod_ref+0x7dd/0xac0 fs/btrfs/extent-tree.c:2523 update_ref_for_cow+0x9cd/0x11f0 fs/btrfs/ctree.c:512 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_insert_empty_items+0x9c/0x1a0 fs/btrfs/ctree.c:4314 btrfs_insert_empty_item fs/btrfs/ctree.h:669 [inline] btrfs_insert_orphan_item+0x1f1/0x320 fs/btrfs/orphan.c:23 btrfs_orphan_add+0x6d/0x1a0 fs/btrfs/inode.c:3482 btrfs_unlink+0x267/0x350 fs/btrfs/inode.c:4293 vfs_unlink+0x365/0x650 fs/namei.c:4469 do_unlinkat+0x4ae/0x830 fs/namei.c:4533 __do_sys_unlinkat fs/namei.c:4576 [inline] __se_sys_unlinkat fs/namei.c:4569 [inline] __x64_sys_unlinkat+0xcc/0xf0 fs/namei.c:4569 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f BTRFS error (device loop0 state EA): Ref action 1, root 5, ref_root 5, parent 0, owner 260, offset 0, num_refs 1 __btrfs_mod_ref+0x76b/0xac0 fs/btrfs/extent-tree.c:2521 update_ref_for_cow+0x96a/0x11f0 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_lookup_inode+0xdc/0x480 fs/btrfs/inode-item.c:411 __btrfs_update_delayed_inode+0x1e7/0xb90 fs/btrfs/delayed-inode.c:1030 btrfs_update_delayed_inode fs/btrfs/delayed-inode.c:1114 [inline] __btrfs_commit_inode_delayed_items+0x2318/0x24a0 fs/btrfs/delayed-inode.c:1137 __btrfs_run_delayed_items+0x213/0x490 fs/btrfs/delayed-inode.c:1171 btrfs_commit_transaction+0x8a8/0x3740 fs/btrfs/transaction.c:2313 prepare_to_relocate+0x3c4/0x4c0 fs/btrfs/relocation.c:3586 relocate_block_group+0x16c/0xd40 fs/btrfs/relocation.c:3611 btrfs_relocate_block_group+0x77d/0xd90 fs/btrfs/relocation.c:4081 btrfs_relocate_chunk+0x12c/0x3b0 fs/btrfs/volumes.c:3377 __btrfs_balance+0x1b0f/0x26b0 fs/btrfs/volumes.c:4161 btrfs_balance+0xbdc/0x10c0 fs/btrfs/volumes.c:4538 BTRFS error (device loop0 state EA): Ref action 2, root 5, ref_root 0, parent 8564736, owner 0, offset 0, num_refs 18446744073709551615 __btrfs_mod_ref+0x7dd/0xac0 fs/btrfs/extent-tree.c:2523 update_ref_for_cow+0x9cd/0x11f0 fs/btrfs/ctree.c:512 btrfs_force_cow_block+0x9f6/0x1da0 fs/btrfs/ctree.c:594 btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754 btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116 btrfs_lookup_inode+0xdc/0x480 fs/btrfs/inode-item.c:411 __btrfs_update_delayed_inode+0x1e7/0xb90 fs/btrfs/delayed-inode.c:1030 btrfs_update_delayed_i ---truncated---

AI Analysis

Technical Summary

CVE-2024-56581 is a high-severity use-after-free vulnerability in the Linux kernel's Btrfs filesystem implementation. The flaw occurs in the btrfs_ref_tree_mod() function, which manages reference entries in the Btrfs extent tree. Specifically, after inserting a new reference entry into a block entry's red-black tree, if an unexpected action (BTRFS_DROP_DELAYED_REF) is encountered, the code erroneously frees the reference entry without first removing it from the red-black tree. This leads to a use-after-free condition when the error path later iterates over block entries and attempts to access the now-freed reference entry. The root cause is improper handling of the reference entry lifecycle in error conditions, resulting in a dangling pointer within the red-black tree structure. The vulnerability is triggered during operations such as file unlinking and block relocation within Btrfs, as evidenced by the detailed stack traces from Syzbot reports. Exploitation could allow a local attacker with limited privileges (PR:L) to cause memory corruption, leading to potential escalation of privileges, arbitrary code execution, or denial of service. The CVSS 3.1 score is 7.8 (high), reflecting the significant impact on confidentiality, integrity, and availability without requiring user interaction. The vulnerability affects Linux kernel versions identified by the commit hash fd708b81d972a0714b02a60eb4792fdbf15868c4 and likely other versions containing the vulnerable code. No known exploits are reported in the wild yet, but the complexity of the bug and its presence in a widely used filesystem make it a critical patching priority for affected systems.

Potential Impact

For European organizations, the impact of CVE-2024-56581 is substantial, especially those relying on Linux servers with Btrfs filesystems. Btrfs is increasingly used in enterprise environments for its advanced features like snapshots and checksumming. Exploitation could allow attackers to execute arbitrary code with elevated privileges or cause system crashes, leading to data loss or service disruption. This is particularly concerning for sectors such as finance, healthcare, government, and critical infrastructure where Linux servers are prevalent. The vulnerability could be leveraged to compromise confidentiality by accessing sensitive data, integrity by corrupting filesystem metadata, and availability by crashing systems or causing kernel panics. Given the local attack vector, insider threats or compromised user accounts could exploit this flaw. The absence of required user interaction simplifies exploitation in multi-user environments. The high severity and potential for privilege escalation make timely patching essential to maintain operational security and compliance with European data protection regulations.

Mitigation Recommendations

1. Immediate application of the official Linux kernel patches that fix the use-after-free condition in btrfs_ref_tree_mod() is the primary mitigation. Monitor Linux kernel mailing lists and vendor advisories for updated stable kernel releases containing the fix. 2. For organizations unable to patch immediately, consider temporarily disabling or avoiding the use of Btrfs filesystems on critical systems to reduce exposure. 3. Implement strict access controls to limit local user privileges, minimizing the risk that a low-privileged user can exploit the vulnerability. 4. Employ kernel hardening techniques such as Kernel Page Table Isolation (KPTI), Kernel Address Space Layout Randomization (KASLR), and use of security modules (e.g., SELinux, AppArmor) to reduce exploitation success. 5. Monitor system logs for unusual Btrfs errors or kernel oops messages indicative of exploitation attempts. 6. Conduct regular audits of user accounts and processes with local access to sensitive Linux servers. 7. Incorporate this vulnerability into vulnerability management and incident response plans to ensure rapid detection and remediation.