ext4: fix bug_on in __es_tree_search caused by bad boot loader inode

In the Linux kernel, the following vulnerability has been resolved:

ext4: fix bug_on in __es_tree_search caused by bad boot loader inode

We got a issue as fllows:

==================================================================

kernel BUG at fs/ext4/extents_status.c:203!

invalid opcode: 0000 [#1] PREEMPT SMP

CPU: 1 PID: 945 Comm: cat Not tainted 6.0.0-next-20221007-dirty #349

RIP: 0010:ext4_es_end.isra.0+0x34/0x42

RSP: 0018:ffffc9000143b768 EFLAGS: 00010203

RAX: 0000000000000000 RBX: ffff8881769cd0b8 RCX: 0000000000000000

RDX: 0000000000000000 RSI: ffffffff8fc27cf7 RDI: 00000000ffffffff

RBP: ffff8881769cd0bc R08: 0000000000000000 R09: ffffc9000143b5f8

R10: 0000000000000001 R11: 0000000000000001 R12: ffff8881769cd0a0

R13: ffff8881768e5668 R14: 00000000768e52f0 R15: 0000000000000000

FS: 00007f359f7f05c0(0000)GS:ffff88842fd00000(0000)knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f359f5a2000 CR3: 000000017130c000 CR4: 00000000000006e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000

DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

Call Trace:

<TASK>

__es_tree_search.isra.0+0x6d/0xf5

ext4_es_cache_extent+0xfa/0x230

ext4_cache_extents+0xd2/0x110

ext4_find_extent+0x5d5/0x8c0

ext4_ext_map_blocks+0x9c/0x1d30

ext4_map_blocks+0x431/0xa50

ext4_mpage_readpages+0x48e/0xe40

ext4_readahead+0x47/0x50

read_pages+0x82/0x530

page_cache_ra_unbounded+0x199/0x2a0

do_page_cache_ra+0x47/0x70

page_cache_ra_order+0x242/0x400

ondemand_readahead+0x1e8/0x4b0

page_cache_sync_ra+0xf4/0x110

filemap_get_pages+0x131/0xb20

filemap_read+0xda/0x4b0

generic_file_read_iter+0x13a/0x250

ext4_file_read_iter+0x59/0x1d0

vfs_read+0x28f/0x460

ksys_read+0x73/0x160

__x64_sys_read+0x1e/0x30

do_syscall_64+0x35/0x80

entry_SYSCALL_64_after_hwframe+0x63/0xcd

</TASK>

==================================================================

In the above issue, ioctl invokes the swap_inode_boot_loader function to

swap inode<5> and inode<12>. However, inode<5> contain incorrect imode and

disordered extents, and i_nlink is set to 1. The extents check for inode in

the ext4_iget function can be bypassed bacause 5 is EXT4_BOOT_LOADER_INO.

While links_count is set to 1, the extents are not initialized in

swap_inode_boot_loader. After the ioctl command is executed successfully,

the extents are swapped to inode<12>, in this case, run the `cat` command

to view inode<12>. And Bug_ON is triggered due to the incorrect extents.

When the boot loader inode is not initialized, its imode can be one of the

following:

1) the imode is a bad type, which is marked as bad_inode in ext4_iget and

set to S_IFREG.

2) the imode is good type but not S_IFREG.

3) the imode is S_IFREG.

The BUG_ON may be triggered by bypassing the check in cases 1 and 2.

Therefore, when the boot loader inode is bad_inode or its imode is not

S_IFREG, initialize the inode to avoid triggering the BUG.