Subject: CVE-2021-47145: btrfs: do not BUG_ON in link_to_fixup_dir

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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

btrfs: do not BUG_ON in link_to_fixup_dir

While doing error injection testing I got the following panic

  kernel BUG at fs/btrfs/tree-log.c:1862!
  invalid opcode: 0000 [#1] SMP NOPTI
  CPU: 1 PID: 7836 Comm: mount Not tainted 5.13.0-rc1+ #305
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
  RIP: 0010:link_to_fixup_dir+0xd5/0xe0
  RSP: 0018:ffffb5800180fa30 EFLAGS: 00010216
  RAX: fffffffffffffffb RBX: 00000000fffffffb RCX: ffff8f595287faf0
  RDX: ffffb5800180fa37 RSI: ffff8f5954978800 RDI: 0000000000000000
  RBP: ffff8f5953af9450 R08: 0000000000000019 R09: 0000000000000001
  R10: 000151f408682970 R11: 0000000120021001 R12: ffff8f5954978800
  R13: ffff8f595287faf0 R14: ffff8f5953c77dd0 R15: 0000000000000065
  FS:  00007fc5284c8c40(0000) GS:ffff8f59bbd00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007fc5287f47c0 CR3: 000000011275e002 CR4: 0000000000370ee0
  Call Trace:
   replay_one_buffer+0x409/0x470
   ? btree_read_extent_buffer_pages+0xd0/0x110
   walk_up_log_tree+0x157/0x1e0
   walk_log_tree+0xa6/0x1d0
   btrfs_recover_log_trees+0x1da/0x360
   ? replay_one_extent+0x7b0/0x7b0
   open_ctree+0x1486/0x1720
   btrfs_mount_root.cold+0x12/0xea
   ? __kmalloc_track_caller+0x12f/0x240
   legacy_get_tree+0x24/0x40
   vfs_get_tree+0x22/0xb0
   vfs_kern_mount.part.0+0x71/0xb0
   btrfs_mount+0x10d/0x380
   ? vfs_parse_fs_string+0x4d/0x90
   legacy_get_tree+0x24/0x40
   vfs_get_tree+0x22/0xb0
   path_mount+0x433/0xa10
   __x64_sys_mount+0xe3/0x120
   do_syscall_64+0x3d/0x80
   entry_SYSCALL_64_after_hwframe+0x44/0xae

We can get -EIO or any number of legitimate errors from
btrfs_search_slot(), panicing here is not the appropriate response.  The
error path for this code handles errors properly, simply return the
error.

The Linux kernel CVE team has assigned CVE-2021-47145 to this issue.

Affected and fixed versions
===========================

	Fixed in 4.4.271 with commit 76bfd8ac20be
	Fixed in 4.9.271 with commit e934c4ee17b3
	Fixed in 4.14.235 with commit 0eaf383c6a4a
	Fixed in 4.19.193 with commit 6eccfb28f8dc
	Fixed in 5.4.124 with commit 0ed102453aa1
	Fixed in 5.10.42 with commit 7e13db503918
	Fixed in 5.12.9 with commit b54544213358
	Fixed in 5.13 with commit 91df99a6eb50

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47145
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/btrfs/tree-log.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/76bfd8ac20bebeae599452a03dfc5724c0475dcf
	https://git.kernel.org/stable/c/e934c4ee17b33bafb0444f2f9766cda7166d3c40
	https://git.kernel.org/stable/c/0eaf383c6a4a83c09f60fd07a1bea9f1a9181611
	https://git.kernel.org/stable/c/6eccfb28f8dca70c9b1b3bb3194ca54cbe73a9fa
	https://git.kernel.org/stable/c/0ed102453aa1cd12fefde8f6b60b9519b0b1f003
	https://git.kernel.org/stable/c/7e13db503918820e6333811cdc6f151dcea5090a
	https://git.kernel.org/stable/c/b545442133580dcb2f2496133bf850824d41255c
	https://git.kernel.org/stable/c/91df99a6eb50d5a1bc70fff4a09a0b7ae6aab96d