tomoyo: don't emit warning in tomoyo_write_control()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: tomoyo: don't emit warning in tomoyo_write_control() syzbot is reporting too large allocation warning at tomoyo_write_control(), for one can write a very very long line without new line character. To fix this warning, I use __GFP_NOWARN rather than checking for KMALLOC_MAX_SIZE, for practically a valid line should be always shorter than 32KB where the "too small to fail" memory-allocation rule applies. One might try to write a valid line that is longer than 32KB, but such request will likely fail with -ENOMEM. Therefore, I feel that separately returning -EINVAL when a line is longer than KMALLOC_MAX_SIZE is redundant. There is no need to distinguish over-32KB and over-KMALLOC_MAX_SIZE.

References

• https://git.kernel.org/stable/c/c67efabddc73171c7771d3ffe4ffa1e503ee533e
• https://git.kernel.org/stable/c/f6b37b3e12de638753bce79a2858070b9c4a4ad3
• https://git.kernel.org/stable/c/b2bd5857a0d6973ebbcb4d9831ddcaebbd257be1
• https://git.kernel.org/stable/c/a01c200fa7eb59da4d2dbbb48b61f4a0d196c09f
• https://git.kernel.org/stable/c/fe1c021eb03dae0dc9dce55e81f77a60e419a27a
• https://git.kernel.org/stable/c/c9382f380e8d09209b8e5c0def0545852168be25
• https://git.kernel.org/stable/c/414705c0303350d139b1dc18f329fe47dfb642dd
• https://git.kernel.org/stable/c/3df7546fc03b8f004eee0b9e3256369f7d096685