Forwarded: [PATCH] nilfs2: fix wrong inode returned from nilfs_iget_for_shadow on cache hit

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Subject: [PATCH] nilfs2: fix wrong inode returned from nilfs_iget_for_shadow  on cache hit
Author: kartikey406@xxxxxxxxx

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


nilfs_iget_for_shadow() returns the original inode instead of the
cached shadow inode when the shadow inode already exists (I_NEW not
set). This causes nilfs_mdt_setup_shadow_map() to store the original
inode as shadow->inode, so subsequent calls to
nilfs_mdt_save_to_shadow_map() dereference the wrong inode's
i_assoc_inode, which may be NULL, leading to a general protection
fault.

This can be triggered by mounting a corrupted NILFS2 image that causes
rollback recovery, followed immediately by NILFS_IOCTL_CLEAN_SEGMENTS.
During rollback, nilfs_dat_read() is called twice, causing
nilfs_iget_for_shadow() to hit the cached path and return the wrong
inode.

Fix this by returning s_inode instead of inode on the cache hit path.

Reported-by: syzbot+4b4093b1f24ad789bf37@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=4b4093b1f24ad789bf37
Signed-off-by: Deepanshu Kartikey <Kartikey406@xxxxxxxxx>
---
 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 51bde45d5865..1f9bc63eb295 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -687,7 +687,7 @@ struct inode *nilfs_iget_for_shadow(struct inode *inode)
 	if (unlikely(!s_inode))
 		return ERR_PTR(-ENOMEM);
 	if (!(inode_state_read_once(s_inode) & I_NEW))
-		return inode;
+		return s_inode;
 
 	NILFS_I(s_inode)->i_flags = 0;
 	memset(NILFS_I(s_inode)->i_bmap, 0, sizeof(struct nilfs_bmap));
-- 
2.43.0