ext4: fix race condition between ext4_write and ext4_convert_inline_data

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

ext4: fix race condition between ext4_write and ext4_convert_inline_data

Hulk Robot reported a BUG_ON:

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

EXT4-fs error (device loop3): ext4_mb_generate_buddy:805: group 0,

block bitmap and bg descriptor inconsistent: 25 vs 31513 free clusters

kernel BUG at fs/ext4/ext4_jbd2.c:53!

invalid opcode: 0000 [#1] SMP KASAN PTI

CPU: 0 PID: 25371 Comm: syz-executor.3 Not tainted 5.10.0+ #1

RIP: 0010:ext4_put_nojournal fs/ext4/ext4_jbd2.c:53 [inline]

RIP: 0010:__ext4_journal_stop+0x10e/0x110 fs/ext4/ext4_jbd2.c:116

[...]

Call Trace:

ext4_write_inline_data_end+0x59a/0x730 fs/ext4/inline.c:795

generic_perform_write+0x279/0x3c0 mm/filemap.c:3344

ext4_buffered_write_iter+0x2e3/0x3d0 fs/ext4/file.c:270

ext4_file_write_iter+0x30a/0x11c0 fs/ext4/file.c:520

do_iter_readv_writev+0x339/0x3c0 fs/read_write.c:732

do_iter_write+0x107/0x430 fs/read_write.c:861

vfs_writev fs/read_write.c:934 [inline]

do_pwritev+0x1e5/0x380 fs/read_write.c:1031

[...]

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

Above issue may happen as follows:

cpu1 cpu2

__________________________|__________________________

do_pwritev

vfs_writev

do_iter_write

ext4_file_write_iter

ext4_buffered_write_iter

generic_perform_write

ext4_da_write_begin

vfs_fallocate

ext4_fallocate

ext4_convert_inline_data

ext4_convert_inline_data_nolock

ext4_destroy_inline_data_nolock

clear EXT4_STATE_MAY_INLINE_DATA

ext4_map_blocks

ext4_ext_map_blocks

ext4_mb_new_blocks

ext4_mb_regular_allocator

ext4_mb_good_group_nolock

ext4_mb_init_group

ext4_mb_init_cache

ext4_mb_generate_buddy --> error

ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)

ext4_restore_inline_data

set EXT4_STATE_MAY_INLINE_DATA

ext4_block_write_begin

ext4_da_write_end

ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA)

ext4_write_inline_data_end

handle=NULL

ext4_journal_stop(handle)

__ext4_journal_stop

ext4_put_nojournal(handle)

ref_cnt = (unsigned long)handle

BUG_ON(ref_cnt == 0) ---> BUG_ON

The lock held by ext4_convert_inline_data is xattr_sem, but the lock

held by generic_perform_write is i_rwsem. Therefore, the two locks can

be concurrent.

To solve above issue, we add inode_lock() for ext4_convert_inline_data().

At the same time, move ext4_convert_inline_data() in front of

ext4_punch_hole(), remove similar handling from ext4_punch_hole().