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libc: Implement getrandom on top of "/dev/[u]random"

Browse Source 
https://man7.org/linux/man-pages/man2/getrandom.2.html

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
This commit is contained in:
Xiang Xiao 2022-03-24 22:31:27 +08:00 committed by Petro Karashchenko
parent 594ae1e7fc
commit c8ea7a95a3
3 changed files with 171 additions and 1 deletions
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79
include/sys/random.h Normal file
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@ -0,0 +1,79 @@
/****************************************************************************
* include/sys/random.h
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
#ifndef __INCLUDE_SYS_RANDOM_H
#define __INCLUDE_SYS_RANDOM_H
/****************************************************************************
* Included Files
****************************************************************************/
#include <stddef.h>
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/* Flags for getrandom(2)
*
* GRND_NONBLOCK Don't block and return EAGAIN instead
* GRND_RANDOM Open /dev/random instead of /dev/urandom
* GRND_INSECURE Return non-cryptographic random bytes
*/
#define GRND_NONBLOCK (1 << 0)
#define GRND_RANDOM (1 << 1)
#define GRND_INSECURE (1 << 2)
/****************************************************************************
* Public Function Prototypes
****************************************************************************/
/****************************************************************************
* Name: getrandom
*
* Description:
* Fill a buffer of arbitrary length with randomness. This is the
* preferred interface for getting random numbers. The traditional
* /dev/random approach is susceptible for things like the attacker
* exhausting file descriptors on purpose.
*
* Note that this function cannot fail, other than by asserting.
*
* Input Parameters:
* bytes - Buffer for returned random bytes
* nbytes - Number of bytes requested.
* flags - Bit mask that can contain zero or more of the ORed values
* together.
*
* Returned Value:
* On success, getrandom() returns the number of bytes that were copied
* to the buffer bytes. This may be less than the number of bytes
* requested via nbytes if either GRND_RANDOM was specified in flags and
* insufficient entropy was present in the random source or the system
* call was interrupted by a signal.
*
* On error, -1 is returned, and errno is set appropriately.
*
****************************************************************************/
ssize_t getrandom(FAR void *bytes, size_t nbytes, unsigned int flags);
#endif /* __INCLUDE_SYS_RANDOM_H */

2
libs/libc/misc/Make.defs
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@ -20,7 +20,7 @@
# Add the internal C files to the build
CSRCS += lib_mknod.c lib_umask.c lib_utsname.c
CSRCS += lib_mknod.c lib_umask.c lib_utsname.c lib_getrandom.c
CSRCS += lib_xorshift128.c lib_tea_encrypt.c lib_tea_decrypt.c
# Support for platforms that do not have long long types

91
libs/libc/misc/lib_getrandom.c Normal file
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/****************************************************************************
* libs/libc/misc/lib_getrandom.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <sys/random.h>
#include <fcntl.h>
#include <unistd.h>
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: getrandom
*
* Description:
* Fill a buffer of arbitrary length with randomness. This is the
* preferred interface for getting random numbers. The traditional
* /dev/random approach is susceptible for things like the attacker
* exhausting file descriptors on purpose.
*
* Note that this function cannot fail, other than by asserting.
*
* Input Parameters:
* bytes - Buffer for returned random bytes
* nbytes - Number of bytes requested.
* flags - Bit mask that can contain zero or more of the ORed values
* together.
*
* Returned Value:
* On success, getrandom() returns the number of bytes that were copied
* to the buffer bytes. This may be less than the number of bytes
* requested via nbytes if either GRND_RANDOM was specified in flags and
* insufficient entropy was present in the random source or the system
* call was interrupted by a signal.
*
* On error, -1 is returned, and errno is set appropriately.
*
****************************************************************************/
ssize_t getrandom(FAR void *bytes, size_t nbytes, unsigned int flags)
{
int oflags = O_RDONLY;
FAR const char *dev;
int fd;
if ((flags & GRND_NONBLOCK) != 0)
{
oflags |= O_NONBLOCK;
}
if ((flags & GRND_RANDOM) != 0)
{
dev = "/dev/random";
}
else
{
dev = "/dev/urandom";
}
fd = open(dev, oflags);
if (fd < 0)
{
return fd;
}
nbytes = read(fd, bytes, nbytes);
close(fd);
return nbytes;
}