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

BugLink: https://bugs.launchpad.net/bugs/1995638
commit d325dc6eb763c10f591c239550b8c7e5466a5d09 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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 35bc52d453a973442b289268ffe52d9f1d1466e8..f4e74fac2c51f799eb1ab71aa9cfebf4bfa42861 100644 (file)
--- 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;