linux-ext4 - [PATCH v2] jbd2: fix data-race and null-ptr-deref in jbd2_journal_dirty

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Message-ID: <20250514130855.99010-1-aha310510@gmail.com>
Date: Wed, 14 May 2025 22:08:55 +0900
From: Jeongjun Park <aha310510@...il.com>
To: tytso@....edu,
	jack@...e.cz
Cc: linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot+de24c3fe3c4091051710@...kaller.appspotmail.com,
	Jeongjun Park <aha310510@...il.com>
Subject: [PATCH v2] jbd2: fix data-race and null-ptr-deref in jbd2_journal_dirty_metadata()

Since handle->h_transaction may be a NULL pointer, so we should change it
to call is_handle_aborted(handle) first before dereferencing it.

And the following data-race was reported in my fuzzer:

==================================================================
BUG: KCSAN: data-race in jbd2_journal_dirty_metadata / jbd2_journal_dirty_metadata

write to 0xffff888011024104 of 4 bytes by task 10881 on cpu 1:
 jbd2_journal_dirty_metadata+0x2a5/0x770 fs/jbd2/transaction.c:1556
 __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358
 ext4_do_update_inode fs/ext4/inode.c:5220 [inline]
 ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869
 __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074
 ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103
....

read to 0xffff888011024104 of 4 bytes by task 10880 on cpu 0:
 jbd2_journal_dirty_metadata+0xf2/0x770 fs/jbd2/transaction.c:1512
 __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358
 ext4_do_update_inode fs/ext4/inode.c:5220 [inline]
 ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869
 __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074
 ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103
....

value changed: 0x00000000 -> 0x00000001
==================================================================

This issue is caused by missing data-race annotation for jh->b_modified.
Therefore, the missing annotation needs to be added.

Reported-by: syzbot+de24c3fe3c4091051710@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=de24c3fe3c4091051710
Fixes: 6e06ae88edae ("jbd2: speedup jbd2_journal_dirty_metadata()")
Signed-off-by: Jeongjun Park <aha310510@...il.com>
---
v2: Changed to annotate jh->b_modified to avoid performance overhead
- Link to v1: https://lore.kernel.org/all/20250513170441.54658-1-aha310510@gmail.com/
---
 fs/jbd2/transaction.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index cbc4785462f5..c7867139af69 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1509,7 +1509,7 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 				jh->b_next_transaction == transaction);
 		spin_unlock(&jh->b_state_lock);
 	}
-	if (jh->b_modified == 1) {
+	if (data_race(jh->b_modified == 1)) {
 		/* If it's in our transaction it must be in BJ_Metadata list. */
 		if (data_race(jh->b_transaction == transaction &&
 		    jh->b_jlist != BJ_Metadata)) {
@@ -1528,7 +1528,6 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 		goto out;
 	}

-	journal = transaction->t_journal;
 	spin_lock(&jh->b_state_lock);

 	if (is_handle_aborted(handle)) {
@@ -1543,6 +1542,8 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 		goto out_unlock_bh;
 	}

+	journal = transaction->t_journal;
+
 	if (jh->b_modified == 0) {
 		/*
 		 * This buffer's got modified and becoming part
--