linux-ext4 - [PATCH v3] ext4: fix i_data_sem unlock order in ext4_ind

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Message-ID: <20240829152210.2754-1-ancowi69@gmail.com>
Date: Thu, 29 Aug 2024 15:22:09 +0000
From: Artem Sadovnikov <ancowi69@...il.com>
To: "Theodore Ts'o" <tytso@....edu>
Cc: Artem Sadovnikov <ancowi69@...il.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lvc-project@...uxtesting.org,
	Ritesh Harjani <ritesh.list@...il.com>,
	Mikhail Ukhin <mish.uxin2012@...dex.ru>
Subject: [PATCH v3] ext4: fix i_data_sem unlock order in ext4_ind_migrate()

Fuzzing reports a possible deadlock in jbd2_log_wait_commit.

This issue is triggered when an EXT4_IOC_MIGRATE ioctl is set to require
synchronous updates because the file descriptor is opened with O_SYNC.
This can lead to the jbd2_journal_stop() function calling
jbd2_might_wait_for_commit(), potentially causing a deadlock if the
EXT4_IOC_MIGRATE call races with a write(2) system call.

This problem only arises when CONFIG_PROVE_LOCKING is enabled. In this
case, the jbd2_might_wait_for_commit macro locks jbd2_handle in the
jbd2_journal_stop function while i_data_sem is locked. This triggers
lockdep because the jbd2_journal_start function might also lock the same
jbd2_handle simultaneously.

Found by Linux Verification Center (linuxtesting.org) with syzkaller.

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Co-developed-by: Mikhail Ukhin <mish.uxin2012@...dex.ru>
Signed-off-by: Mikhail Ukhin <mish.uxin2012@...dex.ru>
Signed-off-by: Artem Sadovnikov <ancowi69@...il.com>
---
 v2: New addresses have been added and Ritesh Harjani has been noted as a
 reviewer.
 v3: Description updated.
 fs/ext4/migrate.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index d98ac2af8199..a5e1492bbaaa 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -663,8 +663,8 @@ int ext4_ind_migrate(struct inode *inode)
 	if (unlikely(ret2 && !ret))
 		ret = ret2;
 errout:
-	ext4_journal_stop(handle);
 	up_write(&EXT4_I(inode)->i_data_sem);
+	ext4_journal_stop(handle);
 out_unlock:
 	ext4_writepages_up_write(inode->i_sb, alloc_ctx);
 	return ret;
-- 
2.43.0