Commit Message
Greg KH
Oct. 24, 2022, 11:29 a.m. UTC
From: Jason A. Donenfeld <Jason@zx2c4.com> commit cd4f24ae9404fd31fc461066e57889be3b68641b upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- drivers/char/mem.c | 4 ++-- drivers/char/random.c | 5 +++++ 2 files changed, 7 insertions(+), 2 deletions(-)
--- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -887,8 +887,8 @@ static const struct memdev { #endif [5] = { "zero", 0666, &zero_fops, 0 }, [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 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1294,6 +1294,11 @@ static ssize_t random_read_iter(struct k { int ret; + if (!crng_ready() && + ((kiocb->ki_flags & IOCB_NOWAIT) || + (kiocb->ki_filp->f_flags & O_NONBLOCK))) + return -EAGAIN; + ret = wait_for_random_bytes(); if (ret != 0) return ret;