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Fixes #4645 -- poll() on /dev/random before reading from /dev/urandom on Linux (#4656)

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* Fixes #4645 -- select() on /dev/random before reading from /dev/urandom on linux

* whoops

* Missing header

* whoops

* Review notes

* Potential uninitialized fix

* Signals are literally impossible
This commit is contained in:
Alex Gaynor 2018-12-29 08:04:32 -06:00 committed by Paul Kehrer
parent 4bf93b7b18
commit 8f75d07797
1 changed files with 56 additions and 18 deletions
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74
src/_cffi_src/openssl/src/osrandom_engine.c
View file

@ -13,6 +13,10 @@
* Copyright 2001-2016 Python Software Foundation; All Rights Reserved.
*/
#ifdef __linux__
#include <poll.h>
#endif
static const char *Cryptography_osrandom_engine_id = "osrandom";
/****************************************************************************
@ -90,9 +94,47 @@ static struct {
ino_t st_ino;
} urandom_cache = { -1 };
static int set_cloexec(int fd) {
int flags = fcntl(fd, F_GETFD);
if (flags == -1) {
return -1;
}
if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1) {
return -1;
}
return 0;
}
#ifdef __linux__
/* On Linux, we open("/dev/random") and use poll() to wait until it's readable
* before we read from /dev/urandom, this ensures that we don't read from
* /dev/urandom before the kernel CSPRNG is initialized. This isn't necessary on
* other platforms because they don't have the same _bug_ as Linux does with
* /dev/urandom and early boot. */
static int wait_on_devrandom(void) {
struct pollfd pfd = {};
int ret = 0;
int random_fd = open("/dev/random", O_RDONLY);
if (random_fd < 0) {
return -1;
}
if (set_cloexec(random_fd) < 0) {
return -1;
}
pfd.fd = random_fd;
pfd.events = POLLIN;
pfd.revents = 0;
do {
ret = poll(&pfd, 1, -1);
} while (ret < 0 && (errno == EINTR || errno == EAGAIN));
close(random_fd);
return ret;
}
#endif
/* return -1 on error */
static int dev_urandom_fd(void) {
int fd, n, flags;
int fd = -1;
struct stat st;
/* Check that fd still points to the correct device */
@ -106,25 +148,25 @@ static int dev_urandom_fd(void) {
}
}
if (urandom_cache.fd < 0) {
#ifdef __linux__
if (wait_on_devrandom() < 0) {
goto error;
}
#endif
fd = open("/dev/urandom", O_RDONLY);
if (fd < 0) {
goto error;
}
if (set_cloexec(fd) < 0) {
goto error;
}
if (fstat(fd, &st)) {
goto error;
}
/* set CLOEXEC flag */
flags = fcntl(fd, F_GETFD);
if (flags == -1) {
goto error;
} else if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1) {
goto error;
}
/* Another thread initialized the fd */
if (urandom_cache.fd >= 0) {
do {
n = close(fd);
} while (n < 0 && errno == EINTR);
close(fd);
return urandom_cache.fd;
}
urandom_cache.st_dev = st.st_dev;
@ -135,9 +177,7 @@ static int dev_urandom_fd(void) {
error:
if (fd != -1) {
do {
n = close(fd);
} while (n < 0 && errno == EINTR);
close(fd);
}
ERR_Cryptography_OSRandom_error(
CRYPTOGRAPHY_OSRANDOM_F_DEV_URANDOM_FD,
@ -177,7 +217,7 @@ static int dev_urandom_read(unsigned char *buffer, int size) {
static void dev_urandom_close(void) {
if (urandom_cache.fd >= 0) {
int fd, n;
int fd;
struct stat st;
if (fstat(urandom_cache.fd, &st)
@ -185,9 +225,7 @@ static void dev_urandom_close(void) {
&& st.st_ino == urandom_cache.st_ino) {
fd = urandom_cache.fd;
urandom_cache.fd = -1;
do {
n = close(fd);
} while (n < 0 && errno == EINTR);
close(fd);
}
}
}