ghsa-6pw8-39hw-qcp8
Vulnerability from github
Published
2024-10-21 18:30
Modified
2024-11-08 18:30
Severity ?
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Details

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

btrfs: fix a NULL pointer dereference when failed to start a new trasacntion

[BUG] Syzbot reported a NULL pointer dereference with the following crash:

FAULT_INJECTION: forcing a failure. start_transaction+0x830/0x1670 fs/btrfs/transaction.c:676 prepare_to_relocate+0x31f/0x4c0 fs/btrfs/relocation.c:3642 relocate_block_group+0x169/0xd20 fs/btrfs/relocation.c:3678 ... BTRFS info (device loop0): balance: ended with status: -12 Oops: general protection fault, probably for non-canonical address 0xdffffc00000000cc: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000660-0x0000000000000667] RIP: 0010:btrfs_update_reloc_root+0x362/0xa80 fs/btrfs/relocation.c:926 Call Trace: commit_fs_roots+0x2ee/0x720 fs/btrfs/transaction.c:1496 btrfs_commit_transaction+0xfaf/0x3740 fs/btrfs/transaction.c:2430 del_balance_item fs/btrfs/volumes.c:3678 [inline] reset_balance_state+0x25e/0x3c0 fs/btrfs/volumes.c:3742 btrfs_balance+0xead/0x10c0 fs/btrfs/volumes.c:4574 btrfs_ioctl_balance+0x493/0x7c0 fs/btrfs/ioctl.c:3673 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893 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

[CAUSE] The allocation failure happens at the start_transaction() inside prepare_to_relocate(), and during the error handling we call unset_reloc_control(), which makes fs_info->balance_ctl to be NULL.

Then we continue the error path cleanup in btrfs_balance() by calling reset_balance_state() which will call del_balance_item() to fully delete the balance item in the root tree.

However during the small window between set_reloc_contrl() and unset_reloc_control(), we can have a subvolume tree update and created a reloc_root for that subvolume.

Then we go into the final btrfs_commit_transaction() of del_balance_item(), and into btrfs_update_reloc_root() inside commit_fs_roots().

That function checks if fs_info->reloc_ctl is in the merge_reloc_tree stage, but since fs_info->reloc_ctl is NULL, it results a NULL pointer dereference.

[FIX] Just add extra check on fs_info->reloc_ctl inside btrfs_update_reloc_root(), before checking fs_info->reloc_ctl->merge_reloc_tree.

That DEAD_RELOC_TREE handling is to prevent further modification to the reloc tree during merge stage, but since there is no reloc_ctl at all, we do not need to bother that.

Show details on source website

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{
  "affected": [],
  "aliases": [
    "CVE-2024-49868"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-476"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-10-21T18:15:06Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix a NULL pointer dereference when failed to start a new trasacntion\n\n[BUG]\nSyzbot reported a NULL pointer dereference with the following crash:\n\n  FAULT_INJECTION: forcing a failure.\n   start_transaction+0x830/0x1670 fs/btrfs/transaction.c:676\n   prepare_to_relocate+0x31f/0x4c0 fs/btrfs/relocation.c:3642\n   relocate_block_group+0x169/0xd20 fs/btrfs/relocation.c:3678\n  ...\n  BTRFS info (device loop0): balance: ended with status: -12\n  Oops: general protection fault, probably for non-canonical address 0xdffffc00000000cc: 0000 [#1] PREEMPT SMP KASAN NOPTI\n  KASAN: null-ptr-deref in range [0x0000000000000660-0x0000000000000667]\n  RIP: 0010:btrfs_update_reloc_root+0x362/0xa80 fs/btrfs/relocation.c:926\n  Call Trace:\n   \u003cTASK\u003e\n   commit_fs_roots+0x2ee/0x720 fs/btrfs/transaction.c:1496\n   btrfs_commit_transaction+0xfaf/0x3740 fs/btrfs/transaction.c:2430\n   del_balance_item fs/btrfs/volumes.c:3678 [inline]\n   reset_balance_state+0x25e/0x3c0 fs/btrfs/volumes.c:3742\n   btrfs_balance+0xead/0x10c0 fs/btrfs/volumes.c:4574\n   btrfs_ioctl_balance+0x493/0x7c0 fs/btrfs/ioctl.c:3673\n   vfs_ioctl fs/ioctl.c:51 [inline]\n   __do_sys_ioctl fs/ioctl.c:907 [inline]\n   __se_sys_ioctl+0xf9/0x170 fs/ioctl.c:893\n   do_syscall_x64 arch/x86/entry/common.c:52 [inline]\n   do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83\n   entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\n[CAUSE]\nThe allocation failure happens at the start_transaction() inside\nprepare_to_relocate(), and during the error handling we call\nunset_reloc_control(), which makes fs_info-\u003ebalance_ctl to be NULL.\n\nThen we continue the error path cleanup in btrfs_balance() by calling\nreset_balance_state() which will call del_balance_item() to fully delete\nthe balance item in the root tree.\n\nHowever during the small window between set_reloc_contrl() and\nunset_reloc_control(), we can have a subvolume tree update and created a\nreloc_root for that subvolume.\n\nThen we go into the final btrfs_commit_transaction() of\ndel_balance_item(), and into btrfs_update_reloc_root() inside\ncommit_fs_roots().\n\nThat function checks if fs_info-\u003ereloc_ctl is in the merge_reloc_tree\nstage, but since fs_info-\u003ereloc_ctl is NULL, it results a NULL pointer\ndereference.\n\n[FIX]\nJust add extra check on fs_info-\u003ereloc_ctl inside\nbtrfs_update_reloc_root(), before checking\nfs_info-\u003ereloc_ctl-\u003emerge_reloc_tree.\n\nThat DEAD_RELOC_TREE handling is to prevent further modification to the\nreloc tree during merge stage, but since there is no reloc_ctl at all,\nwe do not need to bother that.",
  "id": "GHSA-6pw8-39hw-qcp8",
  "modified": "2024-11-08T18:30:44Z",
  "published": "2024-10-21T18:30:56Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-49868"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1282f001cbf56e5dd6e90a18e205a566793f4be0"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/37fee9c220b92c3b7bf22b51c51dde5364e7590b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/39356ec0e319ed07627b3a0f402d0608546509e6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7ad0c5868f2f0418619089513d95230c66cb7eb4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c3b47f49e83197e8dffd023ec568403bcdbb774b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d13249c0df7aab885acb149695f82c54c0822a70"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d73d48acf36f57362df7e4f9d76568168bf5e944"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/dc02c1440705e3451abd1c2c8114a5c1bb188e9f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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