CVE-2021-47508

btrfs: free exchange changeset on failures

Published May 24, 2024 CVSS 3.1 · 5.5 Medium EPSS < 1% KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:

btrfs: free exchange changeset on failures

Fstests runs on my VMs have show several kmemleak reports like the following.

unreferenced object 0xffff88811ae59080 (size 64):
comm "xfs_io", pid 12124, jiffies 4294987392 (age 6.368s)
hex dump (first 32 bytes):
00 c0 1c 00 00 00 00 00 ff cf 1c 00 00 00 00 00 ................
90 97 e5 1a 81 88 ff ff 90 97 e5 1a 81 88 ff ff ................
backtrace:
[<00000000ac0176d2>] ulist_add_merge+0x60/0x150 [btrfs]
[<0000000076e9f312>] set_state_bits+0x86/0xc0 [btrfs]
[<0000000014fe73d6>] set_extent_bit+0x270/0x690 [btrfs]
[<000000004f675208>] set_record_extent_bits+0x19/0x20 [btrfs]
[<00000000b96137b1>] qgroup_reserve_data+0x274/0x310 [btrfs]
[<0000000057e9dcbb>] btrfs_check_data_free_space+0x5c/0xa0 [btrfs]
[<0000000019c4511d>] btrfs_delalloc_reserve_space+0x1b/0xa0 [btrfs]
[<000000006d37e007>] btrfs_dio_iomap_begin+0x415/0x970 [btrfs]
[<00000000fb8a74b8>] iomap_iter+0x161/0x1e0
[<0000000071dff6ff>] __iomap_dio_rw+0x1df/0x700
[<000000002567ba53>] iomap_dio_rw+0x5/0x20
[<0000000072e555f8>] btrfs_file_write_iter+0x290/0x530 [btrfs]
[<000000005eb3d845>] new_sync_write+0x106/0x180
[<000000003fb505bf>] vfs_write+0x24d/0x2f0
[<000000009bb57d37>] __x64_sys_pwrite64+0x69/0xa0
[<000000003eba3fdf>] do_syscall_64+0x43/0x90

In case brtfs_qgroup_reserve_data() or btrfs_delalloc_reserve_metadata()
fail the allocated extent_changeset will not be freed.

So in btrfs_check_data_free_space() and btrfs_delalloc_reserve_space()
free the allocated extent_changeset to get rid of the allocated memory.

The issue currently only happens in the direct IO write path, but only
after 65b3c08606e5 ("btrfs: fix ENOSPC failure when attempting direct IO
write into NOCOW range"), and also at defrag_one_locked_target(). Every
other place is always calling extent_changeset_free() even if its call
to btrfs_delalloc_reserve_space() or btrfs_check_data_free_space() has
failed.

Analysis

No analysis available yet

Remediation

No remediation available yet

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.16:rc1:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.16:rc2:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.16:rc3:*:*:*:*:*:*
cpe:2.3:o:linux:linux_kernel:5.16:rc4:*:*:*:*:*:*
Metrics cvssV3_1

{'score': 4.4, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:L'}

cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Weaknesses
  • CWE-401

    Missing Release of Memory after Effective Lifetime

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
May 11, 2026, 1:56 PM
Reserved
May 22, 2024, 6:20 AM
Status
Analyzed
Published
May 24, 2024, 3:15 PM
Modified
Jun 17, 2026, 4:17 AM
Severity
Low
Public date
May 24, 2024, 12:00 AM