linux-ext4 - [PATCH -next 2/2] jbd2: fix potential use-after-free in jbd2_fc_wait

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Date:   Wed, 14 Sep 2022 18:08:12 +0800
From:   Ye Bin <yebin10@...wei.com>
To:     <tytso@....edu>, <adilger.kernel@...ger.ca>,
        <linux-ext4@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <jack@...e.cz>,
        Ye Bin <yebin10@...wei.com>
Subject: [PATCH -next 2/2] jbd2: fix potential use-after-free in jbd2_fc_wait_bufs

In 'jbd2_fc_wait_bufs' use 'bh' after put buffer head reference count
which may lead to use-after-free.
So judge buffer if uptodate before put buffer head reference count.

Signed-off-by: Ye Bin <yebin10@...wei.com>
---
 fs/jbd2/journal.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 1c833d8cb0fe..4d49f629d06b 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -923,16 +923,16 @@ int jbd2_fc_wait_bufs(journal_t *journal, int num_blks)
 	for (i = j_fc_off - 1; i >= j_fc_off - num_blks; i--) {
 		bh = journal->j_fc_wbuf[i];
 		wait_on_buffer(bh);
-		put_bh(bh);
-		journal->j_fc_wbuf[i] = NULL;
 		/*
 		 * Update j_fc_off so jbd2_fc_release_bufs can release remain
 		 * buffer head.
 		 */
 		if (unlikely(!buffer_uptodate(bh))) {
-			journal->j_fc_off = i;
+			journal->j_fc_off = i + 1;
 			return -EIO;
 		}
+		put_bh(bh);
+		journal->j_fc_wbuf[i] = NULL;
 	}
 
 	return 0;
-- 
2.31.1