Prior to 5.6, when /dev/random was opened with O_NONBLOCK, it would
return -EAGAIN if there was no entropy. When the pools were unified in
5.6, this was lost. The post 5.6 behavior of blocking until the pool is
initialized, and ignoring O_NONBLOCK in the process, went unnoticed,
with no reports about the regression received for two and a half years.
However, eventually this indeed did break somebody's userspace.
So we restore the old behavior, by returning -EAGAIN if the pool is not
initialized. Unlike the old /dev/random, this can only occur during
early boot, after which it never blocks again.
In order to make this O_NONBLOCK behavior consistent with other
expectations, also respect users reading with preadv2(RWF_NOWAIT) and
similar.
Fixes: 30c08efec888 ("random: make /dev/random be almost like /dev/urandom")
Reported-by: Guozihua <guozihua@xxxxxxxxxx>
Reported-by: Zhongguohua <zhongguohua1@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Theodore Ts'o <tytso@xxxxxxx>
Cc: Andrew Lutomirski <luto@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
---
drivers/char/mem.c | 4 ++--
drivers/char/random.c | 5 +++++
2 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 84ca98ed1dad..c2b37009b11e 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -706,8 +706,8 @@ static const struct memdev {
#endif
[5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
[7] = { "full", 0666, &full_fops, 0 },
- [8] = { "random", 0666, &random_fops, 0 },
- [9] = { "urandom", 0666, &urandom_fops, 0 },
+ [8] = { "random", 0666, &random_fops, FMODE_NOWAIT },
+ [9] = { "urandom", 0666, &urandom_fops, FMODE_NOWAIT },
#ifdef CONFIG_PRINTK
[11] = { "kmsg", 0644, &kmsg_fops, 0 },
#endif
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 79d7d4e4e582..c8cc23515568 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1347,6 +1347,11 @@ static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
{
int ret;
+ if (!crng_ready() &&
+ ((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
+ (kiocb->ki_filp->f_flags & O_NONBLOCK)))
+ return -EAGAIN;
+
ret = wait_for_random_bytes();
if (ret != 0)
return ret;
--
2.37.3
