ext4: implementation of a new ioctl called EXT4_IOC_SWAP_BOOT
Add a new ioctl, EXT4_IOC_SWAP_BOOT which swaps i_blocks and
associated attributes (like i_blocks, i_size, i_flags, ...) from the
specified inode with inode EXT4_BOOT_LOADER_INO (#5). This is
typically used to store a boot loader in a secure part of the
filesystem, where it can't be changed by a normal user by accident.
The data blocks of the previous boot loader will be associated with
the given inode.
This usercode program is a simple example of the usage:
int main(int argc, char *argv[])
{
int fd;
int err;
if ( argc != 2 ) {
printf("usage: ext4-swap-boot-inode FILE-TO-SWAP\n");
exit(1);
}
fd = open(argv[1], O_WRONLY);
if ( fd < 0 ) {
perror("open");
exit(1);
}
err = ioctl(fd, EXT4_IOC_SWAP_BOOT);
if ( err < 0 ) {
perror("ioctl");
exit(1);
}
close(fd);
exit(0);
}
[ Modified by Theodore Ts'o to fix a number of bugs in the original code.]
Signed-off-by: Dr. Tilmann Bubeck <t.bubeck@reinform.de>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 769c656..a29bfc2 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4191,8 +4191,9 @@
* NeilBrown 1999oct15
*/
if (inode->i_nlink == 0) {
- if (inode->i_mode == 0 ||
- !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) {
+ if ((inode->i_mode == 0 ||
+ !(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_ORPHAN_FS)) &&
+ ino != EXT4_BOOT_LOADER_INO) {
/* this inode is deleted */
ret = -ESTALE;
goto bad_inode;
@@ -4200,7 +4201,9 @@
/* The only unlinked inodes we let through here have
* valid i_mode and are being read by the orphan
* recovery code: that's fine, we're about to complete
- * the process of deleting those. */
+ * the process of deleting those.
+ * OR it is the EXT4_BOOT_LOADER_INO which is
+ * not initialized on a new filesystem. */
}
ei->i_flags = le32_to_cpu(raw_inode->i_flags);
inode->i_blocks = ext4_inode_blocks(raw_inode, ei);
@@ -4320,6 +4323,8 @@
else
init_special_inode(inode, inode->i_mode,
new_decode_dev(le32_to_cpu(raw_inode->i_block[1])));
+ } else if (ino == EXT4_BOOT_LOADER_INO) {
+ make_bad_inode(inode);
} else {
ret = -EIO;
EXT4_ERROR_INODE(inode, "bogus i_mode (%o)", inode->i_mode);
