[SRU][J][PATCH] nilfs2: fix use-after-free bug of struct nilfs_root

[Yuxuan Luo]

From: Ryusuke Konishi <konishi.ryusuke at gmail.com>

If the beginning of the inode bitmap area is corrupted on disk, an inode
with the same inode number as the root inode can be allocated and fail
soon after.  In this case, the subsequent call to nilfs_clear_inode() on
that bogus root inode will wrongly decrement the reference counter of
struct nilfs_root, and this will erroneously free struct nilfs_root,
causing kernel oopses.

This fixes the problem by changing nilfs_new_inode() to skip reserved
inode numbers while repairing the inode bitmap.

Link: https://lkml.kernel.org/r/20221003150519.39789-1-konishi.ryusuke@gmail.com
Signed-off-by: Ryusuke Konishi <konishi.ryusuke at gmail.com>
Reported-by: syzbot+b8c672b0e22615c80fe0 at syzkaller.appspotmail.com
Reported-by: Khalid Masum <khalid.masum.92 at gmail.com>
Tested-by: Ryusuke Konishi <konishi.ryusuke at gmail.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
(cherry picked from commit d325dc6eb763c10f591c239550b8c7e5466a5d09)
CVE-2022-3649
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 fs/nilfs2/inode.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 2466f8b8be95..0c9ff1c9f817 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -332,6 +332,7 @@ struct inode *nilfs_new_inode(struct inode *dir, umode_t mode)
 	struct inode *inode;
 	struct nilfs_inode_info *ii;
 	struct nilfs_root *root;
+	struct buffer_head *bh;
 	int err = -ENOMEM;
 	ino_t ino;
 
@@ -347,11 +348,25 @@ struct inode *nilfs_new_inode(struct inode *dir, umode_t mode)
 	ii->i_state = BIT(NILFS_I_NEW);
 	ii->i_root = root;
 
-	err = nilfs_ifile_create_inode(root->ifile, &ino, &ii->i_bh);
+	err = nilfs_ifile_create_inode(root->ifile, &ino, &bh);
 	if (unlikely(err))
 		goto failed_ifile_create_inode;
 	/* reference count of i_bh inherits from nilfs_mdt_read_block() */
 
+	if (unlikely(ino < NILFS_USER_INO)) {
+		nilfs_warn(sb,
+			   "inode bitmap is inconsistent for reserved inodes");
+		do {
+			brelse(bh);
+			err = nilfs_ifile_create_inode(root->ifile, &ino, &bh);
+			if (unlikely(err))
+				goto failed_ifile_create_inode;
+		} while (ino < NILFS_USER_INO);
+
+		nilfs_info(sb, "repaired inode bitmap for reserved inodes");
+	}
+	ii->i_bh = bh;
+
 	atomic64_inc(&root->inodes_count);
 	inode_init_owner(&init_user_ns, inode, dir, mode);
 	inode->i_ino = ino;
-- 
2.34.1