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iscsi_create_context: call srand() only once

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iscsi_create_context() calls srand() every time a new context is
generated. That practice is questionable, as the seed does not need to
change before each call to rand(). As a matter of fact, doing so defeats
the purpose of using rand() altogether. Furthermore, the current
implementation is not thread safe.

This improves ISID generation by using /dev/urandom (when available) as
a seed, and calling srand() only once. In case of errors, fallback to
using something similar to the previous implementation (albeit
thread-safe).

Signed-off-by: Felipe Franciosi <felipe@nutanix.com>
This commit is contained in:
Felipe Franciosi
2018-10-05 15:09:07 +01:00
parent a7a14cc66c
commit 41af44eba1
1 changed files with 50 additions and 3 deletions
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53
lib/init.c
View File

@@ -28,6 +28,8 @@
#include <unistd.h>
#endif
#include <fcntl.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
@@ -148,12 +150,58 @@ void iscsi_sfree(struct iscsi_context *iscsi, void* ptr) {
}
}
static bool rd_set = false;
static pthread_mutex_t rd_mutex = PTHREAD_MUTEX_INITIALIZER;
static void
iscsi_srand_init(struct iscsi_context *iscsi) {
unsigned int seed;
int urand_fd;
ssize_t rc;
int err;
if (rd_set) {
/* fast case, seed has been set */
return;
}
err = pthread_mutex_lock(&rd_mutex);
assert(err == 0);
if (rd_set) {
/* another thread initialized it in the meantime */
goto out;
}
urand_fd = open("/dev/urandom", O_RDONLY);
if (urand_fd == -1) {
goto fallback;
}
rc = read(urand_fd, &seed, sizeof(seed));
close(urand_fd);
if (rc == -1) {
goto fallback;
}
srand(seed);
goto out;
fallback:
/* seed based on @iscsi */
srand(getpid() ^ (uint32_t)((uintptr_t) iscsi));
out:
rd_set = true;
err = pthread_mutex_unlock(&rd_mutex);
assert(err == 0);
}
struct iscsi_context *
iscsi_create_context(const char *initiator_name)
{
struct iscsi_context *iscsi;
size_t required = ISCSI_RAW_HEADER_SIZE + ISCSI_DIGEST_SIZE;
static uint32_t ctx_seq = 0;
char *ca;
if (!initiator_name[0]) {
@@ -177,9 +225,8 @@ iscsi_create_context(const char *initiator_name)
iscsi->fd = -1;
srand(time(NULL) ^ getpid() ^ (uint32_t) ((uintptr_t) iscsi) ^ ctx_seq++);
/* initialize to a "random" isid */
iscsi_srand_init(iscsi);
iscsi_set_isid_random(iscsi, rand(), 0);
/* assume we start in security negotiation phase */