ext4: fix bug_on in __es_tree_search

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

ext4: fix bug_on in __es_tree_search

Hulk Robot reported a BUG_ON:

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

kernel BUG at fs/ext4/extents_status.c:199!

[...]

RIP: 0010:ext4_es_end fs/ext4/extents_status.c:199 [inline]

RIP: 0010:__es_tree_search+0x1e0/0x260 fs/ext4/extents_status.c:217

[...]

Call Trace:

ext4_es_cache_extent+0x109/0x340 fs/ext4/extents_status.c:766

ext4_cache_extents+0x239/0x2e0 fs/ext4/extents.c:561

ext4_find_extent+0x6b7/0xa20 fs/ext4/extents.c:964

ext4_ext_map_blocks+0x16b/0x4b70 fs/ext4/extents.c:4384

ext4_map_blocks+0xe26/0x19f0 fs/ext4/inode.c:567

ext4_getblk+0x320/0x4c0 fs/ext4/inode.c:980

ext4_bread+0x2d/0x170 fs/ext4/inode.c:1031

ext4_quota_read+0x248/0x320 fs/ext4/super.c:6257

v2_read_header+0x78/0x110 fs/quota/quota_v2.c:63

v2_check_quota_file+0x76/0x230 fs/quota/quota_v2.c:82

vfs_load_quota_inode+0x5d1/0x1530 fs/quota/dquot.c:2368

dquot_enable+0x28a/0x330 fs/quota/dquot.c:2490

ext4_quota_enable fs/ext4/super.c:6137 [inline]

ext4_enable_quotas+0x5d7/0x960 fs/ext4/super.c:6163

ext4_fill_super+0xa7c9/0xdc00 fs/ext4/super.c:4754

mount_bdev+0x2e9/0x3b0 fs/super.c:1158

mount_fs+0x4b/0x1e4 fs/super.c:1261

[...]

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

Above issue may happen as follows:

-------------------------------------

ext4_fill_super

ext4_enable_quotas

ext4_quota_enable

ext4_iget

__ext4_iget

ext4_ext_check_inode

ext4_ext_check

__ext4_ext_check

ext4_valid_extent_entries

Check for overlapping extents does't take effect

dquot_enable

vfs_load_quota_inode

v2_check_quota_file

v2_read_header

ext4_quota_read

ext4_bread

ext4_getblk

ext4_map_blocks

ext4_ext_map_blocks

ext4_find_extent

ext4_cache_extents

ext4_es_cache_extent

ext4_es_cache_extent

__es_tree_search

ext4_es_end

BUG_ON(es->es_lblk + es->es_len < es->es_lblk)

The error ext4 extents is as follows:

0af3 0300 0400 0000 00000000 extent_header

00000000 0100 0000 12000000 extent1

00000000 0100 0000 18000000 extent2

02000000 0400 0000 14000000 extent3

In the ext4_valid_extent_entries function,

if prev is 0, no error is returned even if lblock<=prev.

This was intended to skip the check on the first extent, but

in the error image above, prev=0+1-1=0 when checking the second extent,

so even though lblock<=prev, the function does not return an error.

As a result, bug_ON occurs in __es_tree_search and the system panics.

To solve this problem, we only need to check that:

1. The lblock of the first extent is not less than 0.

2. The lblock of the next extent is not less than

the next block of the previous extent.

The same applies to extent_idx.