[PATCH 4.9 172/264] random: check for signal_pending() outside of need_resched() check

Greg Kroah-Hartman
2022-06-23T17:06:13Z

From: Jann Horn <jannh@google.com>

commit 1448769c9cdb69ad65287f4f7ab58bc5f2f5d7ba 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: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/char/random.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -550,13 +550,13 @@ static ssize_t get_random_bytes_user(voi
}

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);