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Generate salt using 128bits from arc4random_buf

This commit is contained in:
Mason Simon 2018-05-27 19:19:09 -07:00
parent 44ccc14540
commit fa8830b003
6 changed files with 35 additions and 22 deletions

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@ -2,7 +2,7 @@ FROM ubuntu:latest
WORKDIR .
RUN apt-get update && apt-get install -y curl gcc make git libpcre3-dev zlib1g-dev
RUN apt-get update && apt-get install -y curl gcc make git libpcre3-dev zlib1g-dev libbsd-dev
ADD ipscrub /ipscrub/
ADD Makefile /

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@ -15,7 +15,7 @@
## Security Model
1. On initialization, and again every `PERIOD`, generate `salt` as `HASH(ngx_random() ++ timestamp)`.
1. On initialization, and again every `PERIOD`, generate `salt` using 128bits from `arc4random_buf()`.
2. On each request, generate masked IP address as `HASH(salt ++ IP address)`.
3. Log masked IP address.

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@ -4,7 +4,13 @@ ngx_module_type=HTTP
ngx_module_name=ngx_ipscrub_module
ngx_module_deps="$ngx_addon_dir/src/ngx_ipscrub_support.h $ngx_addon_dir/src/ngx_ipscrub_debug.h"
ngx_module_srcs="$ngx_addon_dir/src/ngx_ipscrub_module.c $ngx_addon_dir/src/ngx_ipscrub_support.c $ngx_addon_dir/src/ngx_ipscrub_debug.c"
ngx_module_libs=SHA1
# On Linux, link with libbsd, to get arc4random.
if [ `uname` = Linux ]; then
ngx_module_libs="SHA1 -lbsd"
else
ngx_module_libs="SHA1"
fi
. auto/module

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@ -42,7 +42,8 @@ static ngx_command_t ngx_ipscrub_commands[] = {
// Globals.
const int default_period_seconds = 10 * 60; // Period between salt changes.
time_t period_start = -1;
long nonce = -1; // Input to salt generation.
#define num_nonce_bytes 16
u_char nonce[num_nonce_bytes]; // Input to salt generation.
static ngx_http_module_t ngx_ipscrub_module_ctx = {
@ -146,7 +147,7 @@ ngx_http_variable_remote_addr_ipscrub(ngx_http_request_t *r, ngx_http_variable_v
// Regenerate salt if past end of period.
time_t now = time(NULL);
if (period_start == -1 || now - period_start > icf->period_seconds) {
rc = randlong(&nonce);
rc = randbytes((u_char *) &nonce, num_nonce_bytes);
if (rc != NGX_OK) {
return NGX_HTTP_INTERNAL_SERVER_ERROR;
}
@ -156,7 +157,7 @@ ngx_http_variable_remote_addr_ipscrub(ngx_http_request_t *r, ngx_http_variable_v
}
salt.data = (u_char *) &nonce;
salt.len = sizeof(nonce);
salt.len = num_nonce_bytes;
// Although ngx_crypt provides a salted SHA function, specified by a salt beginning with {SSHA}, that function exposes the salt in its result. For our security model, this is inappropriate. Instead, we use the regular nginx SHA function specified by {SHA}, and manually combine the nonce and plaintext.
rc = concat(r->pool, r->connection->addr_text, salt, &combined);

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@ -3,6 +3,15 @@
#include "ngx_ipscrub_support.h"
#if (NGX_FREEBSD || NGX_SOLARIS || NGX_DARWIN)
// arc4random is built-in on these platforms.
#elif (NGX_LINUX)
#include <bsd/stdlib.h>
#else
// TODO: test using libbsd on Windows.
#error ipscrub requires arc4random_buf.
#endif
// null_terminate allocates a new, null-terminated string based on input.
ngx_int_t null_terminate(ngx_pool_t *pool, ngx_str_t input, u_char **out)
{
@ -37,23 +46,20 @@ ngx_int_t concat(ngx_pool_t *pool, ngx_str_t prefix, ngx_str_t suffix, u_char **
return NGX_OK;
}
// randlong fills out with secure random bytes and returns NGX_OK iff successful.
ngx_int_t randlong(long *out) {
#if !(NGX_DARWIN || NGX_SOLARIS || NGX_FREEBSD || NGX_LINUX)
// Windows not supported a.t.m.
// TODO: support Windows (https://msdn.microsoft.com/en-us/library/sxtz2fa8.aspx).
return -1;
#endif
int rand = open("/dev/urandom", O_RDONLY);
if (rand < 0) {
return -1;
// randbytes fills out with secure random bytes.
// Return value of NGX_OK indicates success.
// Return value of NGX_ERROR indicates error.
ngx_int_t randbytes(u_char *out, int num_bytes) {
if (out == NULL) {
return NGX_ERROR;
}
if (num_bytes < 1 || num_bytes > 64) {
// Values outside these bounds may indicate parameter usage mistake.
return NGX_ERROR;
}
ssize_t ret = read(rand, out, sizeof(long));
if (ret != sizeof(long)) {
return -1;
}
arc4random_buf(out, num_bytes);
return NGX_OK;
}

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@ -8,6 +8,6 @@
ngx_int_t null_terminate(ngx_pool_t *pool, ngx_str_t input, u_char **hashed);
ngx_int_t concat(ngx_pool_t *pool, ngx_str_t prefix, ngx_str_t suffix, u_char **out);
ngx_int_t randlong(long *out);
ngx_int_t randbytes(u_char *out, int num_bytes);
#endif /* _IPSCRUB_SUPPORT_H_INCLUDED_ */