linux-mm.kvack.org archive mirror
 help / color / mirror / Atom feed
From: Andrew Morton <akpm@linux-foundation.org>
To: akpm@linux-foundation.org, anatoly.trosinenko@gmail.com,
	anton@tuxera.com, jouni.roivas@tuxera.com, linux-mm@kvack.org,
	mm-commits@vger.kernel.org, slava@dubeyko.com,
	stable@vger.kernel.org, torvalds@linux-foundation.org
Subject: [patch 11/13] hfsplus: prevent corruption in shrinking truncate
Date: Fri, 14 May 2021 17:27:33 -0700	[thread overview]
Message-ID: <20210515002733.KxUyvD09_%akpm@linux-foundation.org> (raw)
In-Reply-To: <20210514172634.9018621171d5334ceee97e95@linux-foundation.org>

From: Jouni Roivas <jouni.roivas@tuxera.com>
Subject: hfsplus: prevent corruption in shrinking truncate

I believe there are some issues introduced by commit 31651c607151
("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: 31651c607151f ("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>
---

 fs/hfsplus/extents.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/fs/hfsplus/extents.c~hfsplus-prevent-corruption-in-shrinking-truncate
+++ a/fs/hfsplus/extents.c
@@ -598,13 +598,15 @@ void hfsplus_file_truncate(struct inode
 		res = __hfsplus_ext_cache_extent(&fd, inode, alloc_cnt);
 		if (res)
 			break;
-		hfs_brec_remove(&fd);
 
-		mutex_unlock(&fd.tree->tree_lock);
 		start = hip->cached_start;
+		if (blk_cnt <= start)
+			hfs_brec_remove(&fd);
+		mutex_unlock(&fd.tree->tree_lock);
 		hfsplus_free_extents(sb, hip->cached_extents,
 				     alloc_cnt - start, alloc_cnt - blk_cnt);
 		hfsplus_dump_extent(hip->cached_extents);
+		mutex_lock(&fd.tree->tree_lock);
 		if (blk_cnt > start) {
 			hip->extent_state |= HFSPLUS_EXT_DIRTY;
 			break;
@@ -612,7 +614,6 @@ void hfsplus_file_truncate(struct inode
 		alloc_cnt = start;
 		hip->cached_start = hip->cached_blocks = 0;
 		hip->extent_state &= ~(HFSPLUS_EXT_DIRTY | HFSPLUS_EXT_NEW);
-		mutex_lock(&fd.tree->tree_lock);
 	}
 	hfs_find_exit(&fd);
 
_


  parent reply	other threads:[~2021-05-15  0:27 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-15  0:26 incoming Andrew Morton
2021-05-15  0:27 ` [patch 01/13] mm/hugetlb: fix F_SEAL_FUTURE_WRITE Andrew Morton
2021-05-15  0:27 ` [patch 02/13] mm/hugetlb: fix cow where page writtable in child Andrew Morton
2021-05-15  0:27 ` [patch 03/13] mm, slub: move slub_debug static key enabling outside slab_mutex Andrew Morton
2021-05-15  0:27 ` [patch 04/13] kernel/resource: fix return code check in __request_free_mem_region Andrew Morton
2021-05-15  0:27 ` [patch 05/13] squashfs: fix divide error in calculate_skip() Andrew Morton
2021-05-15  0:27 ` [patch 06/13] userfaultfd: release page in error path to avoid BUG_ON Andrew Morton
2021-05-15  0:27 ` [patch 07/13] ksm: revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()" Andrew Morton
2021-05-15  0:27 ` [patch 08/13] mm: fix struct page layout on 32-bit systems Andrew Morton
2021-05-15  0:27 ` [patch 09/13] kasan: fix unit tests with CONFIG_UBSAN_LOCAL_BOUNDS enabled Andrew Morton
2021-05-15  0:27 ` [patch 10/13] mm/filemap: fix readahead return types Andrew Morton
2021-05-15  0:27 ` Andrew Morton [this message]
2021-05-15  0:27 ` [patch 12/13] docs: admin-guide: update description for kernel.modprobe sysctl Andrew Morton
2021-05-15  0:27 ` [patch 13/13] mm/ioremap: fix iomap_max_page_shift Andrew Morton

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210515002733.KxUyvD09_%akpm@linux-foundation.org \
    --to=akpm@linux-foundation.org \
    --cc=anatoly.trosinenko@gmail.com \
    --cc=anton@tuxera.com \
    --cc=jouni.roivas@tuxera.com \
    --cc=linux-mm@kvack.org \
    --cc=mm-commits@vger.kernel.org \
    --cc=slava@dubeyko.com \
    --cc=stable@vger.kernel.org \
    --cc=torvalds@linux-foundation.org \
    --subject='Re: [patch 11/13] hfsplus: prevent corruption in shrinking truncate' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).