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Add devices+config to make random/urandom behave like BSD #1

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Add devices+config to make random/urandom behave like BSD #1

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eb611e7
Expose a new memory device that behaves like the various BSD's random…
alex Jun 11, 2016
c835b4d
Added a config option to make the whole kernel be good
alex Jun 11, 2016
ce22c56
Oops
alex Jun 11, 2016
1906453
semicolon
alex Jun 11, 2016
57095da
use an unallocated minor device number
alex Jun 11, 2016
bda33de
Change the names to always be random/urandom
alex Jun 12, 2016
aec36e5
Write this conditional correctly
alex Jun 12, 2016
7d28a21
typo; this is what happens when you don' try to build your thing
alex Jun 12, 2016
e26e246
sigh
alex Jun 12, 2016
f9d3424
order the same as regular random
alex Jun 12, 2016
03cb4f5
log a nice message if you're blocking in early boot
alex Jun 12, 2016
2096beb
Don't make a /dev/bsd_random
alex Jun 12, 2016
72a2676
everything is awful
alex Jun 13, 2016
a631989
Let /dev/urandom to initialize from the input pool
nelhage Jun 14, 2016
14939ea
Merge pull request #2 from nelhage/bsd-urandom-device
alex Jun 16, 2016
f54039a
added a comment
alex Jun 16, 2016
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9 changes: 9 additions & 0 deletions drivers/char/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,15 @@ menu "Character devices"

source "drivers/tty/Kconfig"

config BSD_RANDOM
bool "random and urandom behave like they do on BSDs"
default n
help
When "y", the character devices for /dev/random and /dev/urandom behave
as they do on BSDs. This means that /dev/urandom will block if it hasn't
been initialized yet, and /dev/random will behave identically to
/dev/urandom. When "n" (the default), the legacy kernel behavior is used.

config DEVMEM
bool "/dev/mem virtual device support"
default y
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6 changes: 6 additions & 0 deletions drivers/char/mem.c
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Expand Up @@ -797,8 +797,14 @@ static const struct memdev {
#endif
[5] = { "zero", 0666, &zero_fops, 0 },
[7] = { "full", 0666, &full_fops, 0 },
#if CONFIG_BSD_RANDOM
[8] = { "random", 0666, &random_fops, 0 },
[9] = { "urandom", 0666, &urandom_fops, 0 },
#else
[8] = { "bsd_urandom", 0666, &bsd_urandom_fops, 0 },
[9] = { "bsd_urandom", 0666, &bsd_urandom_fops, 0 },
#endif
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This doesn't seem quite right - I think you want

#if CONFIG_BSD_RANDOM
     [8] = { "random", 0666, &bsd_urandom_fops, 0 },
     [9] = { "urandom", 0666, &bsd_urandom_fops, 0 },
#else
     [8] = { "random", 0666, &random_fops, 0 },
     [9] = { "urandom", 0666, &urandom_fops, 0 },
#endif
     [13] = { "bsd_urandom", 0666, &bsd_urandom_fops, 0 }

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So you think the names are significant, and not just "decorative", or they are decorative but changing them is ~backwards incompatible.

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The latter. The Kconfig option is

"When "y", the character devices for /dev/random and /dev/urandom behave as they do on BSDs"

which I think is how the code should behave. (Also I think your code as written would attempt to create two bsd_urandoms? Maybe I'm misunderstanding this line of code.)

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If I understand this correctly, this file doesn't create the actual /dev/urandom and /dev/random, it just internally registers the internal things so when you mknod 1 8 /dev/random and mknod 1 9 /dev/urandom it knows where to find the file_operations corresponding to them. Will change the the names to still be random/urandom though.

[13] = { "bsd_urandom", 0666, &bsd_urandom_fops, 0 },
#ifdef CONFIG_PRINTK
[11] = { "kmsg", 0644, &kmsg_fops, 0 },
#endif
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36 changes: 36 additions & 0 deletions drivers/char/random.c
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Expand Up @@ -1473,6 +1473,21 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
return ret;
}

static ssize_t
bsd_urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
if (unlikely(nonblocking_pool.initialized == 0)) {
if (file->f_flags & O_NONBLOCK) {
return -EAGAIN;
}
wait_event_interruptible(urandom_init_wait, nonblocking_pool.initialized);
if (signal_pending(current)) {
return -ERESTARTSYS;
}
}
return urandom_read(file, buf, nbytes, ppos);
}

static unsigned int
random_poll(struct file *file, poll_table * wait)
{
Expand All @@ -1488,6 +1503,18 @@ random_poll(struct file *file, poll_table * wait)
return mask;
}

static unsigned int
bsd_urandom_poll(struct file *file, poll_table *wait) {
unsigned int mask = 0;

poll_wait(file, &urandom_init_wait, wait);
mask |= POLLIN | POLLRDNORM;
if (ENTROPY_BITS(&input_pool) < random_write_wakeup_bits) {
mask |= POLLOUT | POLLWRNORM;
}
return mask;
}

static int
write_pool(struct entropy_store *r, const char __user *buffer, size_t count)
{
Expand Down Expand Up @@ -1599,6 +1626,15 @@ const struct file_operations urandom_fops = {
.llseek = noop_llseek,
};

const struct file_operations bsd_urandom_fops = {
.read = bsd_urandom_read,
.write = random_write,
.unblocked_ioctl = random_ioctl,
.poll = bsd_urandom_poll,
.fasync = random_fasync,
.llseek = noop_llseek,
}

SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
unsigned int, flags)
{
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2 changes: 1 addition & 1 deletion include/linux/random.h
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Expand Up @@ -29,7 +29,7 @@ extern void get_random_bytes_arch(void *buf, int nbytes);
extern int random_int_secret_init(void);

#ifndef MODULE
extern const struct file_operations random_fops, urandom_fops;
extern const struct file_operations random_fops, urandom_fops, bsd_urandom_fops;
#endif

unsigned int get_random_int(void);
Expand Down