random: check for signal_pending() outside of need_resched() check

stable inclusion
from stable-v5.10.119
commit 9641d9b4303f654636610ac6f001196ec5edd7e5
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5L6BB

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9641d9b4303f654636610ac6f001196ec5edd7e5

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

commit 1448769c upstream.

signal_pending() checks TIF_NOTIFY_SIGNAL and TIF_SIGPENDING, which
signal that the task should bail out of the syscall when possible. This
is a separate concept from need_resched(), which checks
TIF_NEED_RESCHED, signaling that the task should preempt.

In particular, with the current code, the signal_pending() bailout
probably won't work reliably.

Change this to look like other functions that read lots of data, such as
read_zero().

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: NJann Horn <jannh@google.com>
Signed-off-by: NJason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>

drivers/char/random.c

@@ -551,13 +551,13 @@ static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
 	}
 
 	do {
-		if (large_request && need_resched()) {
+		if (large_request) {
 			if (signal_pending(current)) {
 				if (!ret)
 					ret = -ERESTARTSYS;
 				break;
 			}
-			schedule();
+			cond_resched();
 		}
 
 		chacha20_block(chacha_state, output);