nilfs2: fix use-after-free bug of struct nilfs_root

commit 722b63781c5b8d6f87f745bd321ab2e7127b3d46 upstream.

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@gmail.com>
Reported-by: syzbot+b8c672b0e22615c80fe0@syzkaller.appspotmail.com
Reported-by: Khalid Masum <khalid.masum.92@gmail.com>
Tested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index b8ebfb16c8ec8082735ce67628430aa7e19b5459..cf01aa55dd44ce00eee3d382229a6acceea4259c 100644 (file)
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -340,6 +340,7 @@ 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;
 
@@ -355,11 +356,26 @@ 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_msg(sb, KERN_WARNING,
+                         "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_msg(sb, KERN_INFO,
+                         "repaired inode bitmap for reserved inodes");
+       }
+       ii->i_bh = bh;
+
        atomic64_inc(&root->inodes_count);
        inode_init_owner(inode, dir, mode);
        inode->i_ino = ino;