linux-kernel - [PATCH 3.18 116/120] jbd2: dont mark block as modified if the handle is out of credits

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Date:   Thu, 11 Oct 2018 17:34:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Theodore Tso <tytso@....edu>,
        Ben Hutchings <ben@...adent.org.uk>,
        Greg Hackmann <ghackmann@...gle.com>
Subject: [PATCH 3.18 116/120] jbd2: dont mark block as modified if the handle is out of credits

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Theodore Ts'o <tytso@....edu>

commit e09463f220ca9a1a1ecfda84fcda658f99a1f12a upstream.

Do not set the b_modified flag in block's journal head should not
until after we're sure that jbd2_journal_dirty_metadat() will not
abort with an error due to there not being enough space reserved in
the jbd2 handle.

Otherwise, future attempts to modify the buffer may lead a large
number of spurious errors and warnings.

This addresses CVE-2018-10883.

https://bugzilla.kernel.org/show_bug.cgi?id=200071

Signed-off-by: Theodore Ts'o <tytso@....edu>
[bwh: Backported to 3.16: Drop the added logging statement, as it's on
 a code path that doesn't exist here]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Greg Hackmann <ghackmann@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/jbd2/transaction.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1283,11 +1283,11 @@ int jbd2_journal_dirty_metadata(handle_t
 		 * of the transaction. This needs to be done
 		 * once a transaction -bzzz
 		 */
-		jh->b_modified = 1;
 		if (handle->h_buffer_credits <= 0) {
 			ret = -ENOSPC;
 			goto out_unlock_bh;
 		}
+		jh->b_modified = 1;
 		handle->h_buffer_credits--;
 	}