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In the Linux kernel, the following vulnerability has been...

Moderate severity Unreviewed Published Aug 21, 2024 to the GitHub Advisory Database • Updated Sep 11, 2024

Package

No package listedSuggest a package

Affected versions

Unknown

Patched versions

Unknown

Description

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix race between quota rescan and disable leading to NULL pointer deref

If we have one task trying to start the quota rescan worker while another
one is trying to disable quotas, we can end up hitting a race that results
in the quota rescan worker doing a NULL pointer dereference. The steps for
this are the following:

  1. Quotas are enabled;

  2. Task A calls the quota rescan ioctl and enters btrfs_qgroup_rescan().
    It calls qgroup_rescan_init() which returns 0 (success) and then joins a
    transaction and commits it;

  3. Task B calls the quota disable ioctl and enters btrfs_quota_disable().
    It clears the bit BTRFS_FS_QUOTA_ENABLED from fs_info->flags and calls
    btrfs_qgroup_wait_for_completion(), which returns immediately since the
    rescan worker is not yet running.
    Then it starts a transaction and locks fs_info->qgroup_ioctl_lock;

  4. Task A queues the rescan worker, by calling btrfs_queue_work();

  5. The rescan worker starts, and calls rescan_should_stop() at the start
    of its while loop, which results in 0 iterations of the loop, since
    the flag BTRFS_FS_QUOTA_ENABLED was cleared from fs_info->flags by
    task B at step 3);

  6. Task B sets fs_info->quota_root to NULL;

  7. The rescan worker tries to start a transaction and uses
    fs_info->quota_root as the root argument for btrfs_start_transaction().
    This results in a NULL pointer dereference down the call chain of
    btrfs_start_transaction(). The stack trace is something like the one
    reported in Link tag below:

    general protection fault, probably for non-canonical address 0xdffffc0000000041: 0000 [#1] PREEMPT SMP KASAN
    KASAN: null-ptr-deref in range [0x0000000000000208-0x000000000000020f]
    CPU: 1 PID: 34 Comm: kworker/u4:2 Not tainted 6.1.0-syzkaller-13872-gb6bb9676f216 #0
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
    Workqueue: btrfs-qgroup-rescan btrfs_work_helper
    RIP: 0010:start_transaction+0x48/0x10f0 fs/btrfs/transaction.c:564
    Code: 48 89 fb 48 (...)
    RSP: 0018:ffffc90000ab7ab0 EFLAGS: 00010206
    RAX: 0000000000000041 RBX: 0000000000000208 RCX: ffff88801779ba80
    RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
    RBP: dffffc0000000000 R08: 0000000000000001 R09: fffff52000156f5d
    R10: fffff52000156f5d R11: 1ffff92000156f5c R12: 0000000000000000
    R13: 0000000000000001 R14: 0000000000000001 R15: 0000000000000003
    FS: 0000000000000000(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
    CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 00007f2bea75b718 CR3: 000000001d0cc000 CR4: 00000000003506e0
    DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
    Call Trace:

    btrfs_qgroup_rescan_worker+0x3bb/0x6a0 fs/btrfs/qgroup.c:3402
    btrfs_work_helper+0x312/0x850 fs/btrfs/async-thread.c:280
    process_one_work+0x877/0xdb0 kernel/workqueue.c:2289
    worker_thread+0xb14/0x1330 kernel/workqueue.c:2436
    kthread+0x266/0x300 kernel/kthread.c:376
    ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

    Modules linked in:

So fix this by having the rescan worker function not attempt to start a
transaction if it didn't do any rescan work.

References

Published by the National Vulnerability Database Aug 21, 2024
Published to the GitHub Advisory Database Aug 21, 2024
Last updated Sep 11, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS score

0.042%
(5th percentile)

Weaknesses

CVE ID

CVE-2023-52896

GHSA ID

GHSA-7g59-fcf3-5hj5

Source code

No known source code

Dependabot alerts are not supported on this advisory because it does not have a package from a supported ecosystem with an affected and fixed version.

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