7.8

CVE-2022-50067

btrfs: unset reloc control if transaction commit fails in prepare_to_relocate()

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

btrfs: unset reloc control if transaction commit fails in prepare_to_relocate()

In btrfs_relocate_block_group(), the rc is allocated.  Then
btrfs_relocate_block_group() calls

relocate_block_group()
  prepare_to_relocate()
    set_reloc_control()

that assigns rc to the variable fs_info->reloc_ctl. When
prepare_to_relocate() returns, it calls

btrfs_commit_transaction()
  btrfs_start_dirty_block_groups()
    btrfs_alloc_path()
      kmem_cache_zalloc()

which may fail for example (or other errors could happen). When the
failure occurs, btrfs_relocate_block_group() detects the error and frees
rc and doesn't set fs_info->reloc_ctl to NULL. After that, in
btrfs_init_reloc_root(), rc is retrieved from fs_info->reloc_ctl and
then used, which may cause a use-after-free bug.

This possible bug can be triggered by calling btrfs_ioctl_balance()
before calling btrfs_ioctl_defrag().

To fix this possible bug, in prepare_to_relocate(), check if
btrfs_commit_transaction() fails. If the failure occurs,
unset_reloc_control() is called to set fs_info->reloc_ctl to NULL.

The error log in our fault-injection testing is shown as follows:

  [   58.751070] BUG: KASAN: use-after-free in btrfs_init_reloc_root+0x7ca/0x920 [btrfs]
  ...
  [   58.753577] Call Trace:
  ...
  [   58.755800]  kasan_report+0x45/0x60
  [   58.756066]  btrfs_init_reloc_root+0x7ca/0x920 [btrfs]
  [   58.757304]  record_root_in_trans+0x792/0xa10 [btrfs]
  [   58.757748]  btrfs_record_root_in_trans+0x463/0x4f0 [btrfs]
  [   58.758231]  start_transaction+0x896/0x2950 [btrfs]
  [   58.758661]  btrfs_defrag_root+0x250/0xc00 [btrfs]
  [   58.759083]  btrfs_ioctl_defrag+0x467/0xa00 [btrfs]
  [   58.759513]  btrfs_ioctl+0x3c95/0x114e0 [btrfs]
  ...
  [   58.768510] Allocated by task 23683:
  [   58.768777]  ____kasan_kmalloc+0xb5/0xf0
  [   58.769069]  __kmalloc+0x227/0x3d0
  [   58.769325]  alloc_reloc_control+0x10a/0x3d0 [btrfs]
  [   58.769755]  btrfs_relocate_block_group+0x7aa/0x1e20 [btrfs]
  [   58.770228]  btrfs_relocate_chunk+0xf1/0x760 [btrfs]
  [   58.770655]  __btrfs_balance+0x1326/0x1f10 [btrfs]
  [   58.771071]  btrfs_balance+0x3150/0x3d30 [btrfs]
  [   58.771472]  btrfs_ioctl_balance+0xd84/0x1410 [btrfs]
  [   58.771902]  btrfs_ioctl+0x4caa/0x114e0 [btrfs]
  ...
  [   58.773337] Freed by task 23683:
  ...
  [   58.774815]  kfree+0xda/0x2b0
  [   58.775038]  free_reloc_control+0x1d6/0x220 [btrfs]
  [   58.775465]  btrfs_relocate_block_group+0x115c/0x1e20 [btrfs]
  [   58.775944]  btrfs_relocate_chunk+0xf1/0x760 [btrfs]
  [   58.776369]  __btrfs_balance+0x1326/0x1f10 [btrfs]
  [   58.776784]  btrfs_balance+0x3150/0x3d30 [btrfs]
  [   58.777185]  btrfs_ioctl_balance+0xd84/0x1410 [btrfs]
  [   58.777621]  btrfs_ioctl+0x4caa/0x114e0 [btrfs]
  ...
Daten sind bereitgestellt durch National Vulnerability Database (NVD)
Linux ≫ Linux Kernel Version < 4.14.318
Linux ≫ Linux Kernel Version >= 4.15 < 4.19.286
Linux ≫ Linux Kernel Version >= 4.20 < 5.4.247
Linux ≫ Linux Kernel Version >= 5.5 < 5.10.184
Linux ≫ Linux Kernel Version >= 5.11 < 5.15.63
Linux ≫ Linux Kernel Version >= 5.16 < 5.19.4
Linux ≫ Linux Kernel Version6.0 Updaterc1
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EPSS Metriken
Typ Quelle Score Percentile
EPSS FIRST.org 0.19% 0.086
CVSS Metriken
Quelle Base Score Exploit Score Impact Score Vector String
nvd@nist.gov 7.8 1.8 5.9
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE-416 Use After Free

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

https://git.kernel.org/stable/c/ff0e8ed8dfb584575cffc1561f17a1d094e8565b
Patch
https://git.kernel.org/stable/c/dcb11fe0a0a9cca2b7425191b9bf30dc29f2ad0f
Patch
https://git.kernel.org/stable/c/8e546674031fc1576da501e27a8fd165222e5a37
Patch
https://git.kernel.org/stable/c/b60e862e133f646f19023ece1d476d630a660de1
Patch
https://git.kernel.org/stable/c/78f8c2370e3d33e35f23bdc648653d779aeacb6e
Patch
https://git.kernel.org/stable/c/5d741afed0bac206640cc64d77b97853283cf719
Patch
https://git.kernel.org/stable/c/85f02d6c856b9f3a0acf5219de6e32f58b9778eb
Patch