[PATCH 6.18 193/198] nilfs2: fix NULL i_assoc_inode dereference in nilfs_mdt_save_to_shadow_map

Greg Kroah-Hartman
2026-04-20T16:05:28Z

From: Deepanshu Kartikey <kartikey406@gmail.com>

commit 4a4e0328edd9e9755843787d28f16dd4165f8b48 upstream.

The DAT inode's btree node cache (i_assoc_inode) is initialized lazily
during btree operations. However, nilfs_mdt_save_to_shadow_map()
assumes i_assoc_inode is already initialized when copying dirty pages
to the shadow map during GC.

If NILFS_IOCTL_CLEAN_SEGMENTS is called immediately after mount before
any btree operation has occurred on the DAT inode, i_assoc_inode is
NULL leading to a general protection fault.

Fix this by calling nilfs_attach_btree_node_cache() on the DAT inode
in nilfs_dat_read() at mount time, ensuring i_assoc_inode is always
initialized before any GC operation can use it.

Reported-by: syzbot+4b4093b1f24ad789bf37@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=4b4093b1f24ad789bf37
Tested-by: syzbot+4b4093b1f24ad789bf37@syzkaller.appspotmail.com
Fixes: e897be17a441 ("nilfs2: fix lockdep warnings in page operations for btree nodes")
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nilfs2/dat.c | 3 +++
1 file changed, 3 insertions(+)

--- a/fs/nilfs2/dat.c
+++ b/fs/nilfs2/dat.c
@@ -524,6 +524,9 @@ int nilfs_dat_read(struct super_block *s
if (err)
goto failed;

+ err = nilfs_attach_btree_node_cache(dat);
+ if (err)
+ goto failed;
err = nilfs_read_inode_common(dat, raw_inode);
if (err)
goto failed;