Re: [PATCH 1/6] maintenance: add get_random_minute()
From: Junio C Hamano <hidden>
Date: 2023-08-08 18:43:05
Taylor Blau [off-list ref] writes:
I think that's an acceptable price to pay here, since we can drop the
code to remember whether or not srand() has been called or not. Here's a
patch that we could take in that direction:
...
- If a different function also calls `srand()`, the PRNG may start
generating repeated values (if that caller also initialized the PRNG
with `getpid()`).Hmph, I didn't think about that one. I do not think it can be a viable attack vector to attack _this_ code, but the other function might be. But if the other function is worth attacking and attackable, it ought to be using crypto-secure one and not srand(), so this argument may not give us a good justification X-<. Provided if code simplification is a good enough rationale, the patch looks sensible, but I find its use of u64 a bit questionable (though not wrong). I would have expected that the type of "rand" would be the same as backoff_ms and wait_ms, two variables involved in the same expression. Thanks.
quoted hunk
diff --git a/lockfile.c b/lockfile.c index 1d5ed01682..6587d407f4 100644 --- a/lockfile.c +++ b/lockfile.c@@ -107,22 +107,17 @@ static int lock_file_timeout(struct lock_file *lk, const char *path, int n = 1; int multiplier = 1; long remaining_ms = 0; - static int random_initialized = 0; if (timeout_ms == 0) return lock_file(lk, path, flags, mode); - if (!random_initialized) { - srand((unsigned int)getpid()); - random_initialized = 1; - } - if (timeout_ms > 0) remaining_ms = timeout_ms; while (1) { long backoff_ms, wait_ms; int fd; + uint64_t rand; fd = lock_file(lk, path, flags, mode);@@ -135,7 +130,10 @@ static int lock_file_timeout(struct lock_file *lk, const char *path, backoff_ms = multiplier * INITIAL_BACKOFF_MS; /* back off for between 0.75*backoff_ms and 1.25*backoff_ms */ - wait_ms = (750 + rand() % 500) * backoff_ms / 1000; + if (csprng_bytes(&rand, sizeof(uint64_t)) < 0) + return error_errno(_("unable to get random bytes for" + "lockfile backoff")); + wait_ms = (750 + rand % 500) * backoff_ms / 1000; sleep_millisec(wait_ms); remaining_ms -= wait_ms; --2.42.0.rc0.26.g802d811bac.dirty--- >8 ---Thanks, Taylor