The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 1448769c9cdb69ad65287f4f7ab58bc5f2f5d7ba Mon Sep 17 00:00:00 2001 From: Jann Horn jannh@google.com Date: Tue, 5 Apr 2022 18:39:31 +0200 Subject: [PATCH] random: check for signal_pending() outside of need_resched() check
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
diff --git a/drivers/char/random.c b/drivers/char/random.c index 47f01b1482a9..394cbd814a0b 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -549,13 +549,13 @@ 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);