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authorJason A. Donenfeld <Jason@zx2c4.com>2022-09-08 17:14:00 +0300
committerJason A. Donenfeld <Jason@zx2c4.com>2022-09-23 13:27:57 +0300
commitcd4f24ae9404fd31fc461066e57889be3b68641b (patch)
treeb6b6655935101c5924b00a7504cadcb47f3040b0 /drivers/char/random.c
parent504c25cb76a9cb805407f7701b25a1fbd48605fa (diff)
downloadlinux-cd4f24ae9404fd31fc461066e57889be3b68641b.tar.xz
random: restore O_NONBLOCK support
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@huawei.com> Reported-by: Zhongguohua <zhongguohua1@huawei.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Theodore Ts'o <tytso@mit.edu> Cc: Andrew Lutomirski <luto@kernel.org> Cc: stable@vger.kernel.org Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Diffstat (limited to 'drivers/char/random.c')
-rw-r--r--drivers/char/random.c5
1 files changed, 5 insertions, 0 deletions
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;