linux-kernel - [PATCH 2/2] nilfs2: prevent kernel bug at submit_bh

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Date: Wed, 13 Mar 2024 19:58:27 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: syzbot <syzbot+cfed5b56649bddf80d6e@...kaller.appspotmail.com>,
	syzkaller-bugs@...glegroups.com,
	linux-nilfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] nilfs2: prevent kernel bug at submit_bh_wbc()

Fix a bug where nilfs_get_block() returns a successful status when
searching and inserting the specified block both fail inconsistently.
If this inconsistent behavior is not due to a previously fixed bug,
then an unexpected race is occurring, so return a temporary error
-EAGAIN instead.

This prevents callers such as __block_write_begin_int() from
requesting a read into a buffer that is not mapped, which would cause
the BUG_ON check for the BH_Mapped flag in submit_bh_wbc() to fail.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
Fixes: 1f5abe7e7dbc ("nilfs2: replace BUG_ON and BUG calls triggerable from ioctl")
Cc: stable@...r.kernel.org
---
 fs/nilfs2/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 9c334c722fc1..5a888b2c1803 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -112,7 +112,7 @@ int nilfs_get_block(struct inode *inode, sector_t blkoff,
 					   "%s (ino=%lu): a race condition while inserting a data block at offset=%llu",
 					   __func__, inode->i_ino,
 					   (unsigned long long)blkoff);
-				err = 0;
+				err = -EAGAIN;
 			}
 			nilfs_transaction_abort(inode->i_sb);
 			goto out;
-- 
2.34.1