[PATCH v4] f2fs: add check for deleted inode

[Chao Yu]

From: Leo Stone <leocstone@xxxxxxxxx>

The syzbot reproducer mounts a f2fs image, then tries to unlink an
existing file. However, the unlinked file already has a link count of 0
when it is read for the first time in do_read_inode().

Add a check to sanity_check_inode() for i_nlink == 0.

[Chao Yu: rebase the code and fix orphan inode recovery issue]
Reported-by: syzbot+b01a36acd7007e273a83@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=b01a36acd7007e273a83
Fixes: 39a53e0ce0df ("f2fs: add superblock and major in-memory structure")
Signed-off-by: Leo Stone <leocstone@xxxxxxxxx>
Signed-off-by: Chao Yu <chao@xxxxxxxxxx>
---
 fs/f2fs/checkpoint.c | 4 ++++
 fs/f2fs/f2fs.h       | 1 +
 fs/f2fs/inode.c      | 6 ++++++
 3 files changed, 11 insertions(+)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index bd890738b94d..ada2c548645c 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -751,6 +751,8 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
 	if (is_sbi_flag_set(sbi, SBI_IS_WRITABLE))
 		f2fs_info(sbi, "orphan cleanup on readonly fs");
 
+	set_sbi_flag(sbi, SBI_ORPHAN_RECOVERY);
+
 	start_blk = __start_cp_addr(sbi) + 1 + __cp_payload(sbi);
 	orphan_blocks = __start_sum_addr(sbi) - 1 - __cp_payload(sbi);
 
@@ -778,9 +780,11 @@ int f2fs_recover_orphan_inodes(struct f2fs_sb_info *sbi)
 		}
 		f2fs_put_page(page, 1);
 	}
+
 	/* clear Orphan Flag */
 	clear_ckpt_flags(sbi, CP_ORPHAN_PRESENT_FLAG);
 out:
+	clear_sbi_flag(sbi, SBI_ORPHAN_RECOVERY);
 	set_sbi_flag(sbi, SBI_IS_RECOVERED);
 
 	return err;
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 05879c6dc4d6..1c75081c0c14 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1322,6 +1322,7 @@ enum {
 	SBI_IS_CLOSE,				/* specify unmounting */
 	SBI_NEED_FSCK,				/* need fsck.f2fs to fix */
 	SBI_POR_DOING,				/* recovery is doing or not */
+	SBI_ORPHAN_RECOVERY,			/* orphan inodes recovery is doing */
 	SBI_NEED_SB_WRITE,			/* need to recover superblock */
 	SBI_NEED_CP,				/* need to checkpoint */
 	SBI_IS_SHUTDOWN,			/* shutdown by ioctl */
diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index d6ad7810df69..02f1b69d03d8 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c
@@ -386,6 +386,12 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
 		}
 	}
 
+	if (inode->i_nlink == 0 && !is_sbi_flag_set(sbi, SBI_ORPHAN_RECOVERY)) {
+		f2fs_warn(sbi, "%s: inode (ino=%lx) has a link count of 0",
+			  __func__, inode->i_ino);
+		return false;
+	}
+
 	return true;
 }
 
-- 
2.48.1.502.g6dc24dfdaf-goog