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: 30c08efec8
("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>
This commit is contained in:
parent
504c25cb76
commit
cd4f24ae94
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@ -712,8 +712,8 @@ static const struct memdev {
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#endif
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#endif
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[5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
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[5] = { "zero", 0666, &zero_fops, FMODE_NOWAIT },
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[7] = { "full", 0666, &full_fops, 0 },
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[7] = { "full", 0666, &full_fops, 0 },
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[8] = { "random", 0666, &random_fops, 0 },
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[8] = { "random", 0666, &random_fops, FMODE_NOWAIT },
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[9] = { "urandom", 0666, &urandom_fops, 0 },
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[9] = { "urandom", 0666, &urandom_fops, FMODE_NOWAIT },
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#ifdef CONFIG_PRINTK
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#ifdef CONFIG_PRINTK
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[11] = { "kmsg", 0644, &kmsg_fops, 0 },
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[11] = { "kmsg", 0644, &kmsg_fops, 0 },
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#endif
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#endif
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@ -1347,6 +1347,11 @@ static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *iter)
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{
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{
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int ret;
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int ret;
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if (!crng_ready() &&
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((kiocb->ki_flags & (IOCB_NOWAIT | IOCB_NOIO)) ||
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(kiocb->ki_filp->f_flags & O_NONBLOCK)))
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return -EAGAIN;
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ret = wait_for_random_bytes();
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ret = wait_for_random_bytes();
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if (ret != 0)
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if (ret != 0)
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return ret;
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return ret;
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