FKIE_CVE-2026-93800

Vulnerability from fkie_nvd - Published: 2026-09-24 17:17 - Updated: 2026-10-03 11:17
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: btrfs: fix use-after-free on reloc root after error in insert_dirty_subvol() If during relocation we fail in insert_dirty_subvol() because btrfs_update_reloc_root() returned an error, we will leave a root's reloc_root field pointing to a reloc root that was freed instead of NULL, resulting later in a use-after-free, or double free attempt during unmount. The sequence of steps is this: 1) During relocation the call to btrfs_update_reloc_root() in insert_dirty_subvol() fails, so insert_dirty_subvol() returns the error to merge_reloc_root() without adding the root to the list rc->dirty_subvol_roots; 2) Then merge_reloc_root() aborts the current transaction because insert_dirty_subvol() returned an error; 3) Up the call chain, merge_reloc_roots() gets the error, adds the reloc root for root X to the local reloc_roots list and jumps to the 'out' label, where it calls free_reloc_roots() to free all the reloc roots in the local reloc_roots list. This frees the reloc root for root X; 4) We go up the call chain to relocate_block_group() which calls clean_dirty_subvols() to go over dirty roots and set their ->reloc_root field to NULL, but root X is not in the dirty_subvol_roots list, so its ->reloc_root still points to a reloc root; 5) Relocation finishes, with an error and a transaction abort, but the ->reloc_root field for root X still points to the reloc root that was freed in step 3; 6) When unmounting the fs we end up calling: btrfs_free_fs_roots() btrfs_drop_and_free_fs_root() --> calls btrfs_put_root() against root X's ->reloc_root which is not NULL and points to the already freed reloc root in step 4 above Resulting in a use-after-free to a double free attempt. Syzbot reported this with the following dmesg/syslog: [ 106.004389][ T5339] BTRFS error (device loop0 state A): Transaction aborted (error -5) [ 106.014266][ T5339] BTRFS: error (device loop0 state A) in merge_reloc_root:1655: errno=-5 IO failure [ 106.021891][ T1061] BTRFS error (device loop0 state A): error while writing out transaction: -5 [ 106.026964][ T1061] BTRFS warning (device loop0 state A): Skipping commit of aborted transaction. [ 106.033807][ T5340] BTRFS error (device loop0 state A): bdev /dev/loop0 errs: wr 3, rd 0, flush 0, corrupt 0, gen 0 [ 106.039265][ T1061] BTRFS: error (device loop0 state A) in cleanup_transaction:2067: errno=-5 IO failure [ 106.044382][ T5339] BTRFS info (device loop0 state EA): forced readonly [ 106.074329][ T5339] BTRFS: error (device loop0 state EA) in merge_reloc_roots:1887: errno=-5 IO failure [ 106.081004][ T5356] BTRFS info (device loop0 state EA): scrub: started on devid 1 [ 106.085611][ T5339] BTRFS info (device loop0 state EA): balance: ended with status: -30 [ 106.089517][ T5356] BTRFS info (device loop0 state EA): scrub: not finished on devid 1 with status: -30 [ 106.662365][ T5338] BTRFS info (device loop0 state EA): last unmount of filesystem 3a375e4e-b156-4d76-a2ad-16e198ce1409 [ 106.682946][ T5338] ================================================================== [ 106.686574][ T5338] BUG: KASAN: slab-use-after-free in btrfs_put_root+0x2f/0x250 [ 106.690090][ T5338] Write of size 4 at addr ffff88803f978630 by task syz.0.0/5338 [ 106.693173][ T5338] [ 106.694279][ T5338] CPU: 0 UID: 0 PID: 5338 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) [ 106.694293][ T5338] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 106.694300][ T5338] Call Trace: [ 106.694308][ T5338] <TASK> [ 106.694314][ T5338] dump_stack_lvl+0xe8/0x150 [ 106.694331][ T5338] print_address_description+0x55/0x1e0 [ 106.694343][ T5338] ? btrfs_put_root+0x2f/0x250 [ 106.694358][ T5338] print_report+0x58/0x70 [ 106. ---truncated---
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5a247097c5f94b51ffc991b444d998ad6e85875f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/6372dd394ea907cd85a7a8063db320ec73dfaed0
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/83201804efa4a5168be754e1dfc9b2faee760cac
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/97a540d72ebcb21853d11f2a56782fe377f358e7
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9f599d120b2b79d2d937c3935b7cdf2697514283
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a01837ae174a2a968c245a30e6dd010f50eaf05d
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fda1b6636ff1846f00643e791099db5564b547d9
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/btrfs/relocation.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "5a247097c5f94b51ffc991b444d998ad6e85875f",
              "status": "affected",
              "version": "f32b84d7c977e1906a4781b93b3c93090b6cd675",
              "versionType": "git"
            },
            {
              "lessThan": "6372dd394ea907cd85a7a8063db320ec73dfaed0",
              "status": "affected",
              "version": "592fbcd50c99b8adf999a2a54f9245caff333139",
              "versionType": "git"
            },
            {
              "lessThan": "9f599d120b2b79d2d937c3935b7cdf2697514283",
              "status": "affected",
              "version": "592fbcd50c99b8adf999a2a54f9245caff333139",
              "versionType": "git"
            },
            {
              "lessThan": "a01837ae174a2a968c245a30e6dd010f50eaf05d",
              "status": "affected",
              "version": "592fbcd50c99b8adf999a2a54f9245caff333139",
              "versionType": "git"
            },
            {
              "lessThan": "97a540d72ebcb21853d11f2a56782fe377f358e7",
              "status": "affected",
              "version": "592fbcd50c99b8adf999a2a54f9245caff333139",
              "versionType": "git"
            },
            {
              "lessThan": "fda1b6636ff1846f00643e791099db5564b547d9",
              "status": "affected",
              "version": "592fbcd50c99b8adf999a2a54f9245caff333139",
              "versionType": "git"
            },
            {
              "lessThan": "83201804efa4a5168be754e1dfc9b2faee760cac",
              "status": "affected",
              "version": "592fbcd50c99b8adf999a2a54f9245caff333139",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "aa18bc1ff8a51f082d5b3b6d07693797637b4028",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "4cb0aea2e250eee35ccfac5f5395cd8f3238a9e5",
              "versionType": "git"
            },
            {
              "lessThan": "5.10.271",
              "status": "affected",
              "version": "5.10.36",
              "versionType": "semver"
            },
            {
              "lessThan": "5.12",
              "status": "affected",
              "version": "5.11.20",
              "versionType": "semver"
            },
            {
              "lessThan": "5.13",
              "status": "affected",
              "version": "5.12.3",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/btrfs/relocation.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.13"
            },
            {
              "lessThan": "5.13",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.271",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.222",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.189",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.158",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.111",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.53",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix use-after-free on reloc root after error in insert_dirty_subvol()\n\nIf during relocation we fail in insert_dirty_subvol() because\nbtrfs_update_reloc_root() returned an error, we will leave a root\u0027s\nreloc_root field pointing to a reloc root that was freed instead of NULL,\nresulting later in a use-after-free, or double free attempt during\nunmount.\n\nThe sequence of steps is this:\n\n1) During relocation the call to btrfs_update_reloc_root() in\n   insert_dirty_subvol() fails, so insert_dirty_subvol() returns the\n   error to merge_reloc_root() without adding the root to the list\n   rc-\u003edirty_subvol_roots;\n\n2) Then merge_reloc_root() aborts the current transaction because\n   insert_dirty_subvol() returned an error;\n\n3) Up the call chain, merge_reloc_roots() gets the error, adds the\n   reloc root for root X to the local reloc_roots list and jumps to the\n   \u0027out\u0027 label, where it calls free_reloc_roots() to free all the reloc\n   roots in the local reloc_roots list. This frees the reloc root for\n   root X;\n\n4) We go up the call chain to relocate_block_group() which calls\n   clean_dirty_subvols() to go over dirty roots and set their\n   -\u003ereloc_root field to NULL, but root X is not in the dirty_subvol_roots\n   list, so its -\u003ereloc_root still points to a reloc root;\n\n5) Relocation finishes, with an error and a transaction abort, but the\n   -\u003ereloc_root field for root X still points to the reloc root that was\n   freed in step 3;\n\n6) When unmounting the fs we end up calling:\n\n     btrfs_free_fs_roots()\n        btrfs_drop_and_free_fs_root()\n           --\u003e calls btrfs_put_root() against root X\u0027s -\u003ereloc_root\n               which is not NULL and points to the already freed\n               reloc root in step 4 above\n\n  Resulting in a use-after-free to a double free attempt.\n\nSyzbot reported this with the following dmesg/syslog:\n\n   [  106.004389][ T5339] BTRFS error (device loop0 state A): Transaction aborted (error -5)\n   [  106.014266][ T5339] BTRFS: error (device loop0 state A) in merge_reloc_root:1655: errno=-5 IO failure\n   [  106.021891][ T1061] BTRFS error (device loop0 state A): error while writing out transaction: -5\n   [  106.026964][ T1061] BTRFS warning (device loop0 state A): Skipping commit of aborted transaction.\n   [  106.033807][ T5340] BTRFS error (device loop0 state A): bdev /dev/loop0 errs: wr 3, rd 0, flush 0, corrupt 0, gen 0\n   [  106.039265][ T1061] BTRFS: error (device loop0 state A) in cleanup_transaction:2067: errno=-5 IO failure\n   [  106.044382][ T5339] BTRFS info (device loop0 state EA): forced readonly\n   [  106.074329][ T5339] BTRFS: error (device loop0 state EA) in merge_reloc_roots:1887: errno=-5 IO failure\n   [  106.081004][ T5356] BTRFS info (device loop0 state EA): scrub: started on devid 1\n   [  106.085611][ T5339] BTRFS info (device loop0 state EA): balance: ended with status: -30\n   [  106.089517][ T5356] BTRFS info (device loop0 state EA): scrub: not finished on devid 1 with status: -30\n   [  106.662365][ T5338] BTRFS info (device loop0 state EA): last unmount of filesystem 3a375e4e-b156-4d76-a2ad-16e198ce1409\n   [  106.682946][ T5338] ==================================================================\n   [  106.686574][ T5338] BUG: KASAN: slab-use-after-free in btrfs_put_root+0x2f/0x250\n   [  106.690090][ T5338] Write of size 4 at addr ffff88803f978630 by task syz.0.0/5338\n   [  106.693173][ T5338]\n   [  106.694279][ T5338] CPU: 0 UID: 0 PID: 5338 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)\n   [  106.694293][ T5338] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014\n   [  106.694300][ T5338] Call Trace:\n   [  106.694308][ T5338]  \u003cTASK\u003e\n   [  106.694314][ T5338]  dump_stack_lvl+0xe8/0x150\n   [  106.694331][ T5338]  print_address_description+0x55/0x1e0\n   [  106.694343][ T5338]  ? btrfs_put_root+0x2f/0x250\n   [  106.694358][ T5338]  print_report+0x58/0x70\n   [  106.\n---truncated---"
    }
  ],
  "id": "CVE-2026-93800",
  "lastModified": "2026-10-03T11:17:49.673",
  "metrics": {},
  "published": "2026-09-24T17:17:12.870",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5a247097c5f94b51ffc991b444d998ad6e85875f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/6372dd394ea907cd85a7a8063db320ec73dfaed0"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/83201804efa4a5168be754e1dfc9b2faee760cac"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/97a540d72ebcb21853d11f2a56782fe377f358e7"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9f599d120b2b79d2d937c3935b7cdf2697514283"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a01837ae174a2a968c245a30e6dd010f50eaf05d"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fda1b6636ff1846f00643e791099db5564b547d9"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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