linux/fs/hfsplus
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
..
attributes.c hfsplus: fix crash and filesystem corruption when deleting files 2020-04-10 15:36:20 -07:00
bfind.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bitmap.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
bnode.c hfs/hfsplus: clean up unused variables in bnode.c 2017-11-17 16:10:03 -08:00
brec.c hfsplus: fix BUG on bnode parent update 2018-10-31 08:54:13 -07:00
btree.c hfsplus: do not free node before using 2018-11-30 14:56:14 -08:00
catalog.c hfsplus: prevent btree data loss on ENOSPC 2018-10-31 08:54:13 -07:00
dir.c hfsplus: convert to fileattr 2021-04-12 15:04:29 +02:00
extents.c hfsplus: prevent corruption in shrinking truncate 2021-05-14 19:41:32 -07:00
hfsplus_fs.h hfsplus: convert to fileattr 2021-04-12 15:04:29 +02:00
hfsplus_raw.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
inode.c hfsplus: convert to fileattr 2021-04-12 15:04:29 +02:00
ioctl.c hfsplus: convert to fileattr 2021-04-12 15:04:29 +02:00
Kconfig treewide: Add SPDX license identifier - Makefile/Kconfig 2019-05-21 10:50:46 +02:00
Makefile hfsplus: drop ACL support 2018-08-22 10:52:50 -07:00
options.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
part_tbl.c hfsplus: use bio op accessors 2016-06-07 13:41:38 -06:00
super.c block: use an on-stack bio in blkdev_issue_flush 2021-01-27 09:51:48 -07:00
tables.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
unicode.c treewide: Remove uninitialized_var() usage 2020-07-16 12:35:15 -07:00
wrapper.c treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
xattr_security.c acl: handle idmapped mounts 2021-01-24 14:27:17 +01:00
xattr_trusted.c acl: handle idmapped mounts 2021-01-24 14:27:17 +01:00
xattr_user.c acl: handle idmapped mounts 2021-01-24 14:27:17 +01:00
xattr.c acl: handle idmapped mounts 2021-01-24 14:27:17 +01:00
xattr.h hfsplus: drop ACL support 2018-08-22 10:52:50 -07:00