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.

Reported-by: syzbot+7536f77535e5210a5c76@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7536f77535e5210a5c76
Reported-by: Leo Stone <leocstone@gmail.com>
Closes: https://lkml.kernel.org/r/20241216021459.178759-2-leocstone@gmail.com
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

Author: Tetsuo Handa

security/tomoyo/common.c

@@ -2665,7 +2665,7 @@ ssize_t tomoyo_write_control(struct tomoyo_io_buffer *head,
 
 		if (head->w.avail >= head->writebuf_size - 1) {
 			const int len = head->writebuf_size * 2;
-			char *cp = kzalloc(len, GFP_NOFS);
+			char *cp = kzalloc(len, GFP_NOFS | __GFP_NOWARN);
 
 			if (!cp) {
 				error = -ENOMEM;