Commit cd4f24ae authored by Jason A. Donenfeld's avatar Jason A. Donenfeld

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: 30c08efe ("random: make /dev/random be almost like /dev/urandom")
Reported-by: default avatarGuozihua <guozihua@huawei.com>
Reported-by: default avatarZhongguohua <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: default avatarJason A. Donenfeld <Jason@zx2c4.com>
parent 504c25cb
...@@ -712,8 +712,8 @@ static const struct memdev { ...@@ -712,8 +712,8 @@ static const struct memdev {
#endif #endif
[5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT }, [5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
[7] = { "full", 0666, &full_fops, 0 }, [7] = { "full", 0666, &full_fops, 0 },
[8] = { "random", 0666, &random_fops, 0 }, [8] = { "random", 0666, &random_fops, FMODE_NOWAIT },
[9] = { "urandom", 0666, &urandom_fops, 0 }, [9] = { "urandom", 0666, &urandom_fops, FMODE_NOWAIT },
#ifdef CONFIG_PRINTK #ifdef CONFIG_PRINTK
[11] = { "kmsg", 0644, &kmsg_fops, 0 }, [11] = { "kmsg", 0644, &kmsg_fops, 0 },
#endif #endif
......
...@@ -1347,6 +1347,11 @@ static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter) ...@@ -1347,6 +1347,11 @@ static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
{ {
int ret; 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(); ret = wait_for_random_bytes();
if (ret != 0) if (ret != 0)
return ret; return ret;
......
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