Message-ID: <2024110927-CVE-2024-50225-c42a@gregkh>
Date: Sat,  9 Nov 2024 11:15:33 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-50225: btrfs: fix error propagation of split bios

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

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

btrfs: fix error propagation of split bios

The purpose of btrfs_bbio_propagate_error() shall be propagating an error
of split bio to its original btrfs_bio, and tell the error to the upper
layer. However, it's not working well on some cases.

* Case 1. Immediate (or quick) end_bio with an error

When btrfs sends btrfs_bio to mirrored devices, btrfs calls
btrfs_bio_end_io() when all the mirroring bios are completed. If that
btrfs_bio was split, it is from btrfs_clone_bioset and its end_io function
is btrfs_orig_write_end_io. For this case, btrfs_bbio_propagate_error()
accesses the orig_bbio's bio context to increase the error count.

That works well in most cases. However, if the end_io is called enough
fast, orig_bbio's (remaining part after split) bio context may not be
properly set at that time. Since the bio context is set when the orig_bbio
(the last btrfs_bio) is sent to devices, that might be too late for earlier
split btrfs_bio's completion.  That will result in NULL pointer
dereference.

That bug is easily reproducible by running btrfs/146 on zoned devices [1]
and it shows the following trace.

[1] You need raid-stripe-tree feature as it create "-d raid0 -m raid1" FS.

  BUG: kernel NULL pointer dereference, address: 0000000000000020
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: Oops: 0000 [#1] PREEMPT SMP PTI
  CPU: 1 UID: 0 PID: 13 Comm: kworker/u32:1 Not tainted 6.11.0-rc7-BTRFS-ZNS+ #474
  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
  Workqueue: writeback wb_workfn (flush-btrfs-5)
  RIP: 0010:btrfs_bio_end_io+0xae/0xc0 [btrfs]
  BTRFS error (device dm-0): bdev /dev/mapper/error-test errs: wr 2, rd 0, flush 0, corrupt 0, gen 0
  RSP: 0018:ffffc9000006f248 EFLAGS: 00010246
  RAX: 0000000000000000 RBX: ffff888005a7f080 RCX: ffffc9000006f1dc
  RDX: 0000000000000000 RSI: 000000000000000a RDI: ffff888005a7f080
  RBP: ffff888011dfc540 R08: 0000000000000000 R09: 0000000000000001
  R10: ffffffff82e508e0 R11: 0000000000000005 R12: ffff88800ddfbe58
  R13: ffff888005a7f080 R14: ffff888005a7f158 R15: ffff888005a7f158
  FS:  0000000000000000(0000) GS:ffff88803ea80000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000020 CR3: 0000000002e22006 CR4: 0000000000370ef0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   <TASK>
   ? __die_body.cold+0x19/0x26
   ? page_fault_oops+0x13e/0x2b0
   ? _printk+0x58/0x73
   ? do_user_addr_fault+0x5f/0x750
   ? exc_page_fault+0x76/0x240
   ? asm_exc_page_fault+0x22/0x30
   ? btrfs_bio_end_io+0xae/0xc0 [btrfs]
   ? btrfs_log_dev_io_error+0x7f/0x90 [btrfs]
   btrfs_orig_write_end_io+0x51/0x90 [btrfs]
   dm_submit_bio+0x5c2/0xa50 [dm_mod]
   ? find_held_lock+0x2b/0x80
   ? blk_try_enter_queue+0x90/0x1e0
   __submit_bio+0xe0/0x130
   ? ktime_get+0x10a/0x160
   ? lockdep_hardirqs_on+0x74/0x100
   submit_bio_noacct_nocheck+0x199/0x410
   btrfs_submit_bio+0x7d/0x150 [btrfs]
   btrfs_submit_chunk+0x1a1/0x6d0 [btrfs]
   ? lockdep_hardirqs_on+0x74/0x100
   ? __folio_start_writeback+0x10/0x2c0
   btrfs_submit_bbio+0x1c/0x40 [btrfs]
   submit_one_bio+0x44/0x60 [btrfs]
   submit_extent_folio+0x13f/0x330 [btrfs]
   ? btrfs_set_range_writeback+0xa3/0xd0 [btrfs]
   extent_writepage_io+0x18b/0x360 [btrfs]
   extent_write_locked_range+0x17c/0x340 [btrfs]
   ? __pfx_end_bbio_data_write+0x10/0x10 [btrfs]
   run_delalloc_cow+0x71/0xd0 [btrfs]
   btrfs_run_delalloc_range+0x176/0x500 [btrfs]
   ? find_lock_delalloc_range+0x119/0x260 [btrfs]
   writepage_delalloc+0x2ab/0x480 [btrfs]
   extent_write_cache_pages+0x236/0x7d0 [btrfs]
   btrfs_writepages+0x72/0x130 [btrfs]
   do_writepages+0xd4/0x240
   ? find_held_lock+0x2b/0x80
   ? wbc_attach_and_unlock_inode+0x12c/0x290
   ? wbc_attach_and_unlock_inode+0x12c/0x290
   __writeback_single_inode+0x5c/0x4c0
   ? do_raw_spin_unlock+0x49/0xb0
   writeback_sb_inodes+0x22c/0x560
   __writeback_inodes_wb+0x4c/0xe0
   wb_writeback+0x1d6/0x3f0
   wb_workfn+0x334/0x520
   process_one_work+0x1ee/0x570
   ? lock_is_held_type+0xc6/0x130
   worker_thread+0x1d1/0x3b0
   ? __pfx_worker_thread+0x10/0x10
   kthread+0xee/0x120
   ? __pfx_kthread+0x10/0x10
   ret_from_fork+0x30/0x50
   ? __pfx_kthread+0x10/0x10
   ret_from_fork_asm+0x1a/0x30
   </TASK>
  Modules linked in: dm_mod btrfs blake2b_generic xor raid6_pq rapl
  CR2: 0000000000000020

* Case 2. Earlier completion of orig_bbio for mirrored btrfs_bios

btrfs_bbio_propagate_error() assumes the end_io function for orig_bbio is
called last among split bios. In that case, btrfs_orig_write_end_io() sets
the bio->bi_status to BLK_STS_IOERR by seeing the bioc->error [2].
Otherwise, the increased orig_bio's bioc->error is not checked by anyone
and return BLK_STS_OK to the upper layer.

[2] Actually, this is not true. Because we only increases orig_bioc->errors
by max_errors, the condition "atomic_read(&bioc->error) > bioc->max_errors"
is still not met if only one split btrfs_bio fails.

* Case 3. Later completion of orig_bbio for un-mirrored btrfs_bios

In contrast to the above case, btrfs_bbio_propagate_error() is not working
well if un-mirrored orig_bbio is completed last. It sets
orig_bbio->bio.bi_status to the btrfs_bio's error. But, that is easily
over-written by orig_bbio's completion status. If the status is BLK_STS_OK,
the upper layer would not know the failure.

* Solution

Considering the above cases, we can only save the error status in the
orig_bbio (remaining part after split) itself as it is always
available. Also, the saved error status should be propagated when all the
split btrfs_bios are finished (i.e, bbio->pending_ios == 0).

This commit introduces "status" to btrfs_bbio and saves the first error of
split bios to original btrfs_bio's "status" variable. When all the split
bios are finished, the saved status is loaded into original btrfs_bio's
status.

With this commit, btrfs/146 on zoned devices does not hit the NULL pointer
dereference anymore.

The Linux kernel CVE team has assigned CVE-2024-50225 to this issue.


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

	Issue introduced in 6.3 with commit 852eee62d31a and fixed in 6.11.7 with commit 22833d89b780
	Issue introduced in 6.3 with commit 852eee62d31a and fixed in 6.12-rc6 with commit d48e1dea3931

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-2024-50225
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/bio.c
	fs/btrfs/bio.h


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/22833d89b780ba0f9f66e19c477e7decf638edce
	https://git.kernel.org/stable/c/d48e1dea3931de64c26717adc2b89743c7ab6594

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