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Jouni Roivas c3187cf322 hfsplus: prevent corruption in shrinking truncate 
I believe there are some issues introduced by commit 31651c6071
("hfsplus: avoid deadlock on file truncation")

HFS+ has extent records which always contains 8 extents.  In case the
first extent record in catalog file gets full, new ones are allocated from
extents overflow file.

In case shrinking truncate happens to middle of an extent record which
locates in extents overflow file, the logic in hfsplus_file_truncate() was
changed so that call to hfs_brec_remove() is not guarded any more.

Right action would be just freeing the extents that exceed the new size
inside extent record by calling hfsplus_free_extents(), and then check if
the whole extent record should be removed.  However since the guard
(blk_cnt > start) is now after the call to hfs_brec_remove(), this has
unfortunate effect that the last matching extent record is removed
unconditionally.

To reproduce this issue, create a file which has at least 10 extents, and
then perform shrinking truncate into middle of the last extent record, so
that the number of remaining extents is not under or divisible by 8.  This
causes the last extent record (8 extents) to be removed totally instead of
truncating into middle of it.  Thus this causes corruption, and lost data.

Fix for this is simply checking if the new truncated end is below the
start of this extent record, making it safe to remove the full extent
record.  However call to hfs_brec_remove() can't be moved to it's previous
place since we're dropping ->tree_lock and it can cause a race condition
and the cached info being invalidated possibly corrupting the node data.

Another issue is related to this one.  When entering into the block
(blk_cnt > start) we are not holding the ->tree_lock.  We break out from
the loop not holding the lock, but hfs_find_exit() does unlock it.  Not
sure if it's possible for someone else to take the lock under our feet,
but it can cause hard to debug errors and premature unlocking.  Even if
there's no real risk of it, the locking should still always be kept in
balance.  Thus taking the lock now just before the check.

Link: https://lkml.kernel.org/r/20210429165139.3082828-1-jouni.roivas@tuxera.com
Fixes: 31651c6071 ("hfsplus: avoid deadlock on file truncation")
Signed-off-by: Jouni Roivas <jouni.roivas@tuxera.com>
Reviewed-by: Anton Altaparmakov <anton@tuxera.com>
Cc: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Cc: Viacheslav Dubeyko <slava@dubeyko.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2021-05-14 19:41:32 -07:00
arch arm64 fixes and cpucaps.h automatic generation: 2021-05-14 10:52:47 -07:00
block block-5.13-2021-05-09 2021-05-09 13:25:14 -07:00
certs Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
crypto for-5.13/drivers-2021-04-27 2021-04-28 14:39:37 -07:00
Documentation A set of straightforward documentation fixes. 2021-05-12 15:38:38 -07:00
drivers drm fixes for 5.13-rc1 2021-05-14 10:38:16 -07:00
fs hfsplus: prevent corruption in shrinking truncate 2021-05-14 19:41:32 -07:00
include mm/filemap: fix readahead return types 2021-05-14 19:41:32 -07:00
init Merge branch 'akpm' (patches from Andrew) 2021-05-07 00:34:51 -07:00
ipc ipc/sem.c: spelling fix 2021-05-07 00:26:34 -07:00
kernel kernel/resource: fix return code check in __request_free_mem_region 2021-05-14 19:41:32 -07:00
lib kasan: fix unit tests with CONFIG_UBSAN_LOCAL_BOUNDS enabled 2021-05-14 19:41:32 -07:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm ksm: revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()" 2021-05-14 19:41:32 -07:00
net mm: fix struct page layout on 32-bit systems 2021-05-14 19:41:32 -07:00
samples Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
scripts Kbuild updates for v5.13 (2nd) 2021-05-08 10:00:11 -07:00
security trusted-keys: match tpm_get_ops on all return paths 2021-05-12 22:36:37 +03:00
sound sound fixes for 5.13-rc1 2021-05-07 11:40:18 -07:00
tools arm64 fixes and cpucaps.h automatic generation: 2021-05-14 10:52:47 -07:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt kvm: Cap halt polling at kvm->max_halt_poll_ns 2021-05-07 06:06:22 -04:00
.clang-format cxl for 5.12 2021-02-24 09:38:36 -08:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap Merge drm/drm-fixes into drm-misc-fixes 2021-05-11 13:35:52 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: move Murali Karicheri to credits 2021-04-29 15:47:30 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS A BO list maintainance fix for TTM, removing an unused function and a 2021-05-14 09:19:38 +10:00
Makefile Linux 5.13-rc1 2021-05-09 14:17:44 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.