Forwarded: [PATCH] nilfs2: fix NULL i_assoc_inode dereference in nilfs_mdt_save_to_shadow_map

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Subject: [PATCH] nilfs2: fix NULL i_assoc_inode dereference in nilfs_mdt_save_to_shadow_map
Author: kartikey406@xxxxxxxxx

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master


When nilfs_dat_read() is called a second time during rollback recovery
from a corrupted segment (checksum error), nilfs_iget_locked() returns
a cached DAT inode that is not I_NEW, causing the function to skip
nilfs_mdt_setup_shadow_map(). This leaves i_assoc_inode as NULL in the
DAT inode, which later causes a general protection fault in
nilfs_mdt_save_to_shadow_map() when NILFS_IOCTL_CLEAN_SEGMENTS is
invoked immediately after mount.

Fix this by redirecting the non-I_NEW path to a new reinit_shadow label
that calls nilfs_mdt_setup_shadow_map() if the shadow map has not been
initialized yet, ensuring i_assoc_inode is always valid before the
segment cleaner uses it.

Reported-by: syzbot+4b4093b1f24ad789bf37@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=4b4093b1f24ad789bf37
Signed-off-by: Deepanshu Kartikey <Kartikey406@xxxxxxxxx>
---
 fs/nilfs2/dat.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/nilfs2/dat.c b/fs/nilfs2/dat.c
index 674380837ab9..c0b656e1c4ef 100644
--- a/fs/nilfs2/dat.c
+++ b/fs/nilfs2/dat.c
@@ -507,7 +507,7 @@ int nilfs_dat_read(struct super_block *sb, size_t entry_size,
 	if (unlikely(!dat))
 		return -ENOMEM;
 	if (!(inode_state_read_once(dat) & I_NEW))
-		goto out;
+		goto reinit_shadow;
 
 	err = nilfs_mdt_init(dat, NILFS_MDT_GFP, sizeof(*di));
 	if (err)
@@ -529,6 +529,14 @@ int nilfs_dat_read(struct super_block *sb, size_t entry_size,
 		goto failed;
 
 	unlock_new_inode(dat);
+	goto out;
+reinit_shadow:
+	di = NILFS_DAT_I(dat);
+	if (!di->mi.mi_shadow) {
+		err = nilfs_mdt_setup_shadow_map(dat, &di->shadow);
+		if (err)
+			goto failed;
+	}
  out:
 	*inodep = dat;
 	return 0;
-- 
2.43.0